Electronic Projects

October 10, 2021September 25, 2023

My Tesla Solar Adventure

The Order

25 June 2021

After research and talking with several solar companies, we decided on an 8.5kW Tesla Solar plus Powerwall+ system with their new high efficiency 425W panels. The main reason for our decision was the low cost, handsomely framed panels and the whole house backup capability. Other solar companies had good backups systems but we did not find any who would provide whole house backup. And, more importantly, we were delightfully surprised to see that Tesla came in with the best price. Having said that, we would soon discover that they seemed to have significantly reduced overhead by mostly eliminating customer service.

The Install

25 September 2021

After ordering, reviewing designs, applying for HOA and City approval, we were finally ready to get the system installed. Two different crews arrived over a span of a week to get the system installed. The panels went on first. The panel install crew was professional and friendly. However, when they left I noticed that the handsome skirts (frames) we were so excited about were only installed on the front of the house (street facing roof). It looked great but I had expected to get them on the back as well. I reported it and in just a few days a technician came out and added the skirts to the back roof panels. He explained that they usually only install the skirts on the front. So, please note, if you want skirts on all your panels, make sure you let them know in advance. Also, the skirts are only put on the left, right and bottom. There are no skirts on the top to allow heat to escape from the panels during the hot summer.

While installing the skirts for the back, I noticed one of the panel edges was sticking up about 1/2″ higher than the rest. The technician tried to fix it but he didn’t have all the tools. He only had what was needed to install the skirts. He asked me if I had a Torx T30 driver. I didn’t but he explained how I could adjust the panels myself. I picked up a T30 at our Newhall True Value store. I climbed up on the roof and found the adjustment area. I used a vice grip on the screwdriver to get enough leverage (mostly because I’m pretty weak especially when I’m up on the roof). I was able to lower the panel 1/2″ so it was flush. It looked beautiful.

A week later, another crew showed up to wire it in and commission the system. This meant a day without power, but we were prepared for that. I tried not to be a nuisance, but couldn’t help but watch and ask questions. I made sure all of the crew had plenty of bottled water, Gatorade and snacks, including ice cream candy bars since it was so hot. They installed the Powerwalls in our garage and wired in the breaker panels and Tesla Gateway by the utility meter. After everything was installed, they powered it up and began the commissioning process.

The Problem

During commissioning, the first signs of trouble started showing up. The installers downloaded the latest software updates but were unable to get the Solar Panels to work correctly. The solar assembly was only producing 160W in full sun which doesn’t even show up in the app. They tried for hours, upgrading, rebooting, calling. They eventually gave up after showing me that the Powerwall could power our house if they cut the mains (based on 22% charge from the factory). They explained that Tesla would send out a software patch to fix the Solar panels, most likely.

I contacted our Tesla Advisor to report the problem and to see if they had an update. After several days of emailing, texting and calling, I received a note from the advisor that our inspection would be scheduled in 3-4 weeks and he would contact the electrician about the problem. I spent another week requesting updates but my Advisor had gone radio silent. It turns out that this is a common experience with Tesla. Assuming best intentions, I can only imagine that the advisors are understaffed and overwhelmed. Regardless, it all results in a very frustrating experience for the customer.

I did manage to finally get an update and a promise to further investigate the issue. While I waited, I decided to do some more research on the system to see if I could find the problem myself…

HIGH VOLTAGE WARNING: I need to stop here and remind everyone that these systems contain extremely high voltages and are dangerous. Hopefully it goes without saying, but please be careful if you poke around inside these electrical boxes. High voltage can be fatal.

The Investigation

You can connect to the Tesla Gateway by scanning the QR code inside the box. It will have your phone connect to the Gateway’s access point. You will need to stay close to the gateway if you connect this way (and browse to https://192.168.91.1). However, keep in mind that it is also connected to your home network and if you know how to find the IP address, you can point your browser to that IP and login as the Installer to see more details about the system. Your browser will likely require that you ignore the security certificate warning (more on this in the observations section below) and you will need to toggle the power switch to one of your Powerwalls but it will let you in. That is essentially their 2nd factor system to ensure you are authorized. Here is what my system looked like after installation on the main screen and on the “System” screen :

The System screen also shows details about the solar generation, Powerwalls and power usage:

Below the above list was a section for “Remote Meter” that would occasionally appear. This was particularly interesting:

Remote Meter (Vxxxxxxxxxxxxxxx)
CT 1 (Solar): —W

That seemed odd. Also when I clicked on the solar panel icon on the main screen, it would say “Stale Meter Data” – that had me wondering if the solar meter was the real issue.

The Fix?

I first disabled the Solar Assembly by clicking “Disable” on the System screen.

I opened up the Inverter, the box above the first Powerall. There is a small latch on the bottom that will unlock and let the panel swing up. I found a wooden dowel to prop it open so it would bang on my head the whole time I was investigating.

I noticed that there was a box on the right that had a “n” LED flashing. The code on the box was the same code that was listed as the “Remote meter” in the system’s display (the one showing no power). Some more research and I discovered that this module is a Neurio W2-Tesla WiFi based current reader that sends the solar power data to the Gateway.

Neurio was recently purchased by Generac but you can still find manuals and some models for sale online. This particular model, W2, has been customized for Tesla. It is designed to connect to the access point of the Tesla Gateway and send the solar power data.

CT-1 Amp Probe Wire

The Neurio has a wire plugged in to the top in the CT-1 (current transformer) port. I traced it over to the solar inverter where a clamp is wrapped around the solar inverter output AC line to measure the amperage. I re-seated that connector.

Antenna

I then noticed that there was an antenna jammed below it that was tucked to the left, under the massive metal inverter shield. I turned the antenna to the right, in the open unshield space.

As soon as I did these two things, the LED “n” on the box began to change and a tune started coming out of the box. It sounded like “I am connected now”. The flashing “n” became a solid blue light.

Eureka!

I went back to the System screen and re-activated the Solar Assembly by clicking “Enabled”. This takes several minutes and you will see the system go through and activate the solar arrays, test relays and impedance before the assembly comes online.

As soon as the Solar Assembly came online, I started seeing kW of power show up on the Systems screen. 5800W of power was coming in, fully powering the house and charging the Powerwalls!

Not so fast…

Sadly, just two hours later my elation was destroyed. The solar energy dropped back to zero.

I checked the inverter. Sure enough, the Neurio was flashing again. I attempt the above process again, several times, but no joy this time. It would chime and go green, but then started flashing again. Based on my research, the Neurio connects to the Tesla Gateway WiFi only. The beeps and flashes indicate that it is unable to connect to the Gateway WiFi.

One thought I had was to reach out to Neurio (which is now owned by Generac) to see if they could provide the API, pinout or schematics for the W2 device so I could troubleshoot at the firmware and component level. When I contacted them, Generac replied that the serial number for my device contains proprietary firmware by Tesla that they cannot support. They recommend that I contact Tesla at: 888-518-3752. Oh well, it was worth a shot.

The Workaround

I love a challenge. In fact, when something isn’t working, it is almost an addiction to me. I have to figure it out and fix it! So, I had two thoughts at this point. First, I wanted to see what the Neurio was actually doing. I thought about setting up an ESP8266 to be an WiFi access point to intercept the Neurio’s communication attempts with the Gateway. But before I do that, it occured to me, I wonder what would happen if the system didn’t have a solar meter at all. In my investigation, I discovered that the solar power meter feature is often an add-on or post-install enhancement. Maybe this was more of an add-on feature than a requirement?

At the minimum, I wanted to see if there are alternatives to the Neurio in the Tesla configuration. Unfortunately, there isn’t an easy way to edit this data. I discovered that settings could only be set during the initial setup time. That would require running the setup wizard again. I decided to be bold and fire up the installation Wizard. At the bottom of the system portal is the “Run Wizard” link. Of course, I clicked it.

WARNING: I’m fairly confident that you can completely break your Tesla Solar setup using the Wizard, maybe even disable power to your house permanently. It is intended for installers. I’m taking the risk, but you should consider this first and be cautious about proceeding. I’m also fairly confident I’m going to void something in the process, but if you put something in my house, fair game, I must hack.

The wizard is straightforward. It requires you to Stop the system, but the settings are mostly intuitive. When I arrived at the Meter screen, it had 3 different meters displayed. I apologize, I did not take screenshots but will update this blog if I capture them in the future but the screens are very basic.

Two of the sensors were for the built-in CT’s used to measure the power in the Tesla Backup Gateway (you can see them on the main bus if you open the Gateway panel – which I did).

Tesla Backup Gateway
**DANGER**: High voltage – Seriously!

These tested extremely fast (subsecond) were working correctly and tested “good”. The third meter, a WiFi meter, was the Solar Meter (Neurio) and it’s status was Error, unable to connect. I clicked the connect button which reported it would take 3 minutes to configure the WiFi sensor. No shock, it didn’t work. I tried it 3 more times. The “Advanced” drop down allows you to add MAC address and IP, but this didn’t help. There was a “Delete” button. I thought it might be worth a try to delete and re-add. At the bottom were options to add “WiFi” or “Wired” CTs. I tried to add the Neurio (WiFi) again, multiple times, rebooting the Neurio occasionally to see if that would help. Nothing.

Here is where something interesting happened. The Wizard would NOT let me advance because the WiFi sensor was not healthy (connected). Hum… Well, I figured I would just have to delete it to see what other screens I could find in the Wizard. I deleted the Neurio. I advanced to the next screen and was presented with a “Warning – you do not have a solar sensor selected.” Naturally, I ignored that and continued.

Commissioned! I completed the Wizard setup and the system came back online. Surprisingly, the system screen looked basically the same but the dynamic flow diagram was actually working. There were no sensor errors or warnings. Power was flowing from the Grid to the House. It was the middle of the night so I signed off and went to bed.

I know what you are thinking. This is dangerous, right? I mean, we seemed to have removed solar power observability from the platform. Will the Gateway and Inverter sill know what to do? Well, it turns out… it does!

The Power of the Sun

Next morning, I woke to discover solar generation was charging the powerwalls and our house was completely powered by the sun! I still want Telsa to fix the Neurio or, better yet, provide some hardwire CT to monitor Solar power generation. I’m assuming that the display below means that the Gateway is computing the the solar generation based on other CTs. In any case, my workaround is in place and we now have a working system again.

As I’m looking at my phone, I realize… I’m holding the power of the sun in the palm of my hand. Yes, that is a geeky Doc Ock reference. We are now powering our home with an ancient but reliable and self-regulating, thermonuclear fusion reactor… our sun.

The Return of Tesla

1 November 2021

I gave up on waiting on Tesla to respond to me about the Neurio. I figured it didn’t matter since I had a working system. A month after the install and I still didn’t have an inspection date. Then it happened. I received a text message and email from Tesla that my inspection was scheduled. There was NO DATE or TIME given. Instead of asking, I figured it didn’t matter. We would see what would happen.

The day of inspection had arrived. A surprise knock on the door and there was Ishmael from Tesla. He explained he was there to meet with the City inspector for the final inspection. I showed him the gear, the Powerwalls, the gateway and the breaker panels. He looked at me and asked, “Did the install crew not put on the warning labels?” Nope.

This was something I had noticed after the installers left. In the Tesla plans are specific instructions on where to place the red warning labels on all of the gear. It includes a helpful diagram for anyone wanting to know how to kill all power in case of emergency. I had raised this issue with my project advisor a few times, but as usual, told me he would look into it and of course, nothing happened. I explained this to Ishmael who rolled his eyes and expressed apologies and said he would need to call to get the labels or it would not pass inspection. He would wait for the delivery and get them installed and ready for the City.

Shortly after meeting Ishmael, another Tesla vehicle pulled up. I figured it was the inspection stickers, but instead, it was Rocío, a Quality Assurance technician. She told me that her job was to make sure everything was installed correctly and running. I almost hugged her! I expressed my delight and appreciation that she would check on us. I explained everything that happened including how the installers said it must have been a Tesla software bug and gave up after trying for hours to get it work. I also told her about the Neurio hack I had done to get it working. She was shocked, sympathetic and determined to fix the issue.

Naturally, Rocío attempted to reset the Neurio and discovered the same thing that I did, with the exception that she was able to get the Neurio to work if she held the connector, pressing on it in a certain way. “There is clearly something wrong with the hardware and it needs to be replaced,” she concluded. I hate to be cynical, but I was definitely thinking this new chapter in my Tesla adventure would turn into an multi-week RMA, repair order and a return visit that may get scheduled sometime next year, if I’m lucky.

To my delight, Rocío looked straight at me and said, “And we’re going to get this fixed today!” She was right! She made a phone call and 30 minutes later another Tesla van showed up with the replacement Neurio!

Rocío got it working. Less than 30 minutes later she had the entire system back online and working correctly. “That’s amazing!” I told her. She clearly saw my astonishment and said, “I used to be an installer, I know what’s needed.” Well, that was completely accurate. She didn’t stop there. She examined all the gear and climbed up on the roof to ensure all the panels were in good order.

Shortly after the good news, the warning labels arrived and were attached to the new gear, ready for the official inspection. I started passing out my sincere appreciation, candy bars, water and Gatorade to these brilliant Tesla soldiers that had come to save the day. After bidding farewell to our new friends, Rocío drove off on her shiney white stallion… uh, I mean Tesla van.

About 30 minutes later, the City Inspector arrived and after a quick survey of the installed gear with Ishmael, signed his approval. Now we are on to the Permission to Operate (PTO) by Southern California Edison.

Power Gremlins

3 November 2021

I should definitely learn to be more guarded in my optimism about this Tesla adventure. After two days of having the new Neurio re-installed, I started noticing something odd. After solar production when I would expect the Powerwalls to kick in and power the house, I would see grid power start to show up and the Powerwalls drop to zero. It would only last for a few minutes then return to normal operations. Looked at the Powerwall Dashboard I set up and can even see the grid power spiking during the day when solar production was more than enough to power the house.

Powerwall Dashboard: Notice the purple (grid power) spikes throughout the day.
These just started showing up after the new Neurio was installed.

The grid power spikes did not exist before the new Neurio. I went out to look at the inverter. The Neurio’s purple light was mostly solid but would “flicker” blue. It was random, like a candle flame not like the error condition of the previous Neurio. It was happening constantly as I watched. When the flickering would get bad, I would see the powerwall drop to zero and grid power surge. There seemed to be a correlation. At any rate, I wasn’t going to let the flickering continue.

HIGH VOLTAGE WARNING: I need to stop here again and remind everyone that these systems contain extremely high voltages and are dangerous. Hopefully it goes without saying, but please be careful if you poke around inside these electrical boxes. High voltage can be fatal.

I powered off the Neurio by unplugging the power next to the antenna at the bottom. I noticed the antenna was once again tucked under the massive shield. I guess that was the typical install. I changed it so it was pointing away from the inverter shield and reworked the cables to plug it back in. The Neurio went through the startup (flashing, then solid green, then blue and then purple). I watched it for a while and noticed it stayed solid purple, no flickering.

I don’t know if this was a fix or a sign of things to come. Other people have reported similar problems with the Neurio, including a YouTube video on how to reset it the way I did. It is rather shocking how unreliable this little box is. I understand it is a “revenue grade” meter which is likely why Tesla is using it, allowing them to report “Solar Renewable Energy Credits” (SRECs). The Inverter itself seems to have a decent meter without the Neurio which is why my workaround hack worked while waiting for the Neurio replacement. If the reset doesn’t work, I will likely revisit my “fix.”

5 January 2022

The “fix” was temporary. It appears to be a resource leak that requires the Neurio to be restarted. The good news is that Tesla finally recognized the instability and sent out a 21.44 firmware update that fixed the Powerwall from disabling solar when the Neurio goes into a bad state. Finally! I was planning on ripping the Neurio out after PTO, but now I don’t have to do that. I’m currently on firmware 21.44.1 and just heard from the community that others are seeing an upgrade to 22.1 that also upgrades the Neurio from firmware “1.6.1-Tesla” to “1.7.1-Tesla” (you have to access the vitals API and decode the protobuf binary payload to see this – see here). Hopefully that helps with stability.

Permission to Operate

2 February 2022

PTO, finally! Our utility company, Southern California Edison (SCE) granted permission to operate. It took Tesla several tries to get the PTO request submitted correctly. SCE was notifying us of all the transactions but we were not able to see the full application or help. Believe me, I tried! In any case, our installation adventure has finally come to an end. It has been seven months since we started this epic journey. It is good to finally have a fully operational system.

To be fair, we have had a working solar system with Powerwall backup since October, but without PTO. PTO means that our system is no longer in self-consumption test mode. We can now push excess solar production to the grid for a credit. For the first time ever, we see grid graph going negative!

24 hour graph of energy usage including Powerwall (green) charging and pushing to the grid (purple).

Conclusion

The Tesla Solar system has been an adventure for us. I don’t regret going with Tesla even though they have improvement areas, especially related to consumer experience. We love the look of the panels and the equipment. In typical Tesla fashion, the design is stunning and feels like quality. If you do select Tesla Solar, my advice is to plan on being the project manager. Stay on top of the details to keep things moving and make sure items are not dropped.

Regardless of who you go with, I recommend you set some non-negotiables to help you filter. Here were my non-negotiables:

Aesthetics – We wanted something that looked high-tech, neat, clean and symmetrical on our roof. I wanted the dark panels (no white lines) with a clean looking frame.
Whole House Backup – We wanted batteries capable of running our house over 24 hours in the event of a power outage and a system that would charge the batteries during the day even if power was out for extended days.
Home Automation and Monitoring APIs – I wanted a system I could hack, use tools to monitor, dashboard, trend and even make decision on home automation components to optimize our energy usage.
Off the Grid – We wanted the system sized to allow us to be self sustaining with no need to use the grid even at night, fully expecting that at some point Net Energy Metering disappears or becomes less attractive, the system will still provide us with a zero grid usage option.

This helped considerably. It eliminated the list down to a handful and the lowest cost on our list was Tesla, who also had the best aesthetics IMHO. Now to be clear, as I mentioned above, Tesla is seeing explosive demand for their option and their customer service struggles a lot. I also had the opportunity to work with several incredible Tesla technicians who helped us.

I am extremely happy with our Tesla system and would recommend it to anyone, despite the bumps along the way. Tesla hit on all my non-negotiables and is elegant, fun and powerful. It has become a delightful hobby as well as a powerful utility for our green energy mission.

While a similar adventure may not be for everyone, if you are in the market for a Solar system, I still highly recommend checking out Tesla’s options. Use this link and you can save $300 if you do order and I get a reward too: http://ts.la/jason50054

Fun Toys

I have to confess. I love toys. To me, this new Tesla Powerwall+ Energy systems is a gigantic (and expensive) toy. I have thoroughly enjoyed tinkering with the system and building electronic accessories and software to manage it. As you have seen in this post, I wrote my own python API library (pyPowerwall) and created a Powerwall Dashboard to better see what the system is doing over time (credit to other open source projects I mention below).

One thing that the Tesla is missing is a good instrument panel display. Sure, you can run the app all the time, but I wanted something that would show the solar production and other details like a physical dashboard but without opening an app. I built one. It is hanging next to the Powerwalls in our garage. Much to my wife’s initial trepidation, I also built one and hung it in our kitchen. It turns out that I’m not the only one to appreciate it… well, after a while anyway. 🙂

Here are some of my toys that I gladly share with you. Please reach out and let me know if you find these useful:

Powerwall Web Dashboard – The Tesla App and web based portal present great animations showing the solar generation and usage. However, the information is very limited and not design for visualizing the energy data in multiple ways. I wanted to see a year at a glance as well as the string data (how much power each group of solar panels on the roof are producing). I found this Grafana based dashboard and made some minor changes including the addition of my own python based Powerwall API Proxy. Here is a simple python API module pyPowerwall to pull data from the Powerwall Gateway using your “customer” credentials: https://github.com/jasonacox/pypowerwall. If you are wanting your own Powerwall Dashboard, it is fairly easy to set up with the instructions here using Docker Compose: https://github.com/jasonacox/Powerwall-Dashboard#powerwall-dashboard

Powerwall Wall Mounted Display – I really wanted to see the current solar generation and state of the Powerwall on a simple LED digital display. I 3D printed a Tesla themed case and installed the displays to show solar, house, battery, and grid power data. The display show the solar production power at the top. House, Powerwall and Grid power data rotate through the middle display and the battery level of the Powerwalls is at the bottom (89% in this picture). You can see a video of the display running below.

The display uses a WiFi enabled systems-on-chip (SoC) ESP8266 WeMos controller and three simple TM1637 7-segment LED display modules. Naturally I used my own Arduino API library (TM1637TinyDisplay) for those and the pyPowerwall proxy to display the results. It would have been nice if Tesla had built a wall monitor to show vitals like this. I’m sure it would have been a nice animated OLED display of some sorts. But this was fun. I needed to build another toy and I love my retro-LED display. If you want to build your own, I have open sourced the design and code and uploaded here for you to use: https://github.com/jasonacox/Powerwall-Display

Observations and Suggestions

I took note of several areas of concern and improvement during my investigation and problem solving. I have recorded them here.

WPA TKIP Command Access Point – The Tesla Gateway uses this weaker method to host its WiFi access point. As I discovered the Neurio uses this same access point to send Solar Power data (if it works). WPA TKIP has been dropped due for security reasons and more modern access points use WPA2 and AES encryption (WPA2-AES).
HTTPS Security Certificate – The HTTPS certificate the Gateway uses will create a browser warning (or error) when you go to the system control portal, either via your home network or via the access point at https://192.168.91.1.
Second Factor – For setup, the user is required to toggle the switch on a Powerwall as a 2nd factor to prove authorization, which is a good thing. That works well for me since my Powerwalls are locked in my garage, but if your Powerwalls are outside next to the Gateway, an attacker on-location could easily join and toggle without you even knowing.
IoT Sensors – The main problem on my system was the Neurio W2 WiFi based sensor. This IoT device sends back power data it measure to the Gateway controller. Generally, this is an elegant way to handle transmitting sensor data between systems without having to wire things. The irony is that the Gateway and Inverter already have several wires and control signal between them. Why not add another wire and avoid any WiFi communication outages? Hopefully I will be able to replace my Neurio with a wired solution.
Solar System Plan – I asked the Tesla Advisor to provide me with the design plans developed for the City Permit. They do not provide this without asking. I am glad I asked. The plans have all the schematics for the wiring as well as the layout. I discovered several things that I wanted changed and was able to get them to update before they came onsite. If you wait until they come onsite, they may not have the materials to make the adjustment and, worse, could charge you for any changes.

References and Notes

I found the following github projects, references and diagrams during my investigation into my Tesla Solar Adventure. I’m pasting them all here to be helpful for anyone else experiencing the same problems. The information may not be directly related but could provide a clue.

Github Projects

pyPowerwall (shameless plug) – Python Module to pull data from the Powerwall Gateway using your customer credentials: https://github.com/jasonacox/pypowerwall
Powerwall Dashboard (2nd shameless plug) – Grafana based dashboard project that let’s you visualize and drill into the Powerwall+ data – https://github.com/jasonacox/Powerwall-Dashboard#powerwall-dashboard
TESLA PowerWall 2 Security Shenanigans – https://github.com/hackerschoice/thc-tesla-powerwall2-hack
Tesla Powerwall 2 – Local Gateway API documentation – https://github.com/vloschiavo/powerwall2
Powerwall Monitoring – https://github.com/mihailescu2m/powerwall_monitor
Python Tesla Powerwall API – https://github.com/jrester/tesla_powerwall

Neurio W2 LED Indicator

https://support-pwrview.generac.com/s/article/Troubleshooting-Networking-Issues

Tesla Powerwall Installation – Metering Installation (link)

messages_0 (1).jpeg — https://teslamotorsclub.com/tmc/threads/tesla-inverter-neurio

June 7, 2020November 11, 2020

ATtiny85 Weather Station

This project will show you how to build an ATtiny85 based mini Weather Station that displays temperature, humidity and pressure using four easy to read 7-segment LEDs.

Requirements

This sketch requires a version of the Wire library that is compatible with the ATtiny85 for the I2C communication to work with the BME-280 sensor. I used the ATTinyCore arduino core by Spence Konde which has a version of the Wire library that works with the ATtiny85. I was able to use the standard Adafruit_BME280 library to pull data from the BME-280. You can install ATTinyCore by putting the board manager URL in the Arduino IDE preferences:

http://drazzy.com/package_drazzy.com_index.json

Set the board to the ATtiny85 chip at 1Mhz (internal).

Circuit

Components:

ATiny85 Microcontroller (DigiKey)
BME-280 Sensor (Temperature, Pressure, Humidity) (Amazon)
74HC595 8-bit Shift Register (Qty 4) (DigiKey)

Sensors

7-Segment LED Display (Qty 4) (DigiKey)
0.1uF Ceramic Capacitor (Qty 2)
100uF Electrolytic Capacitor
5V Power Supply (Alternatively you can use a 5V Solar cell, 3.7V lithium ion battery and a TP4056 constant-current/constant-voltage linear charger to charge the battery during the day).

Schematic

ATtiny85 Microcontroller

Programming Notes:

Code for this project is located on Github: https://github.com/jasonacox/ATtiny85-Weather-Station

I2C communication with BME-280 uses pins PB0/SDA and PB2/SCL. If you use the Tiny AVR Programmer from Sparkfun or something similar, keep in mind that it drives an LED on PB0 which will interfere with I2C communication. You will need to remove the chip from the programmer after uploading to get it to work in the circuit.

Memory Warning

This sketch uses nearly all of the ATtiny85 program storage space (8K) so you may get an overflow error if the libraries change or you add any code. To address this, I created a minimized BME280 library to reduce the PROGMEM space required. You will need to download and install the Tiny_BME280_Library library in:

~/Documents/Arduino/libraries/ directory and restart the Arduino IDE.

Display

  [ 70'] - Temperature in degree F 
  [ 24r] - Relative Humidity %
  [_970] - Pressure in hPa with rising/falling animation
  [ 21c] - Temperature in degree C

Construction

I used two circuit boards: Display and Logic board. The Display board holds the four 7-segment LEDs with the array of resistors. On the back are header pins that plug in to the logic board. The Logic board holds the 4 register chips and the ATtiny85. On the back are headers for the Display board to plug in.

Logic and Display boards:

Both boards together and running:

I printed a simple cylinder case (Thingiverse) to mount the weather station and have it on the back patio:

Power Supply

The circuit will run on 5V or 3.3V. I used an existing solar panel, battery and TP4056 charger circuit to power this project with a 3.3V regulator.

Solar Power Option

1 x 2.5W 5V/500mAh Solar Cell – Amazon
1 x 5V Micro USB 1A TP4056 Lithium Battery Charging Board with Protection Charger Module Amazon
1 x 3.7V 3000mAh 755068 Battery Rechargeable Lithium Polymer ion Battery Pack – Amazon
1 x 3.3V Linear Regulator 250MA MCP1700-3302E/TO – DigiKey

May 3, 2020June 22, 2020

ATtiny85 Ultrasonic Distance Measurement for Parking Help

After discovering the tiny but mighty ATtiny85 microcontroller, I decided to put it to use to help me park my car in the garage. Sure, I could continue to use the softball hung from the ceiling to let me know when I have the car pulled in far enough, but why not take advantage of some tech and have it show me instead? Alternatively, for these times, it is also a fun way to clearly demonstrate 6ft social distancing. 😉

ATiny85 Microcontroller

The ATtiny85 has 5 GPIO easily usable pins (technically you can even use Reset pin as a 6th GPIO but that makes it much more difficulty to reprogram). For information about how to program the ATtiny85, see my previous blog post here.

The tiny but mighty ATtiny85 Microcontroller Pinout

For my “Parking Helper” project I decided to use the low cost entry level ultrasonic distance sensor, the HC-SR04 and two 7-Segment LEDs to show the distance between the device and the front of the car.

HC-SR04 Ultrasonic Sensor

The HC-SR04 has 4 pins: VCC, Trig, Echo and Gnd. The Trig and Echo lines will be driven by the Attiny85.

The HC-SR04 measures distances by sending (TRIG) an sound pulse and measuring the time it takes for the ECHO. Sound travels through air at 332 meters per second at 20 °C (68 °F). Using this the unit provides a duration pulse back to the controller that can be used to determine the distance.

The speed of sound is: 343m/s = 0.0343 cm/uS = 1/29.1 cm/uS

I found a great project here where the author uses the HC-SR04 as an ultrasonic rule. Using the ATtiny85 to trigger and receive the duration pulse we can determine the distance to the parked car.

// Send TRIG HIGH for 10 microseconds 
// to trigger the HC-SR04 to send a sound pulse
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

// Read the ECHO duration
  duration = pulseIn(echoPin, HIGH);

// convert the duration to cm
  distance = (duration / 2) / 29.1;

LED Display (2 Segment)

Driving the display with two 7-segment LEDs is a bit more complicated. Each segment has 7 LEDs to form the numbers plus one LED for the decimal point. That would require 8 GPIO ports for each LED Display or a total of 16 GPIOs! The ATtiny85 has only 5 available for use so we need another way. Thankfully, we can use two low cost 8-bit shift registers (74HC585) and get by with using only 3 GPIO and still drive the 16 LEDs on the two displays.

74HC595 8-bit Shift Register to Drive 7-Segment LED Display

Here is how it works… The ATtiny85 sends the binary data for the the numbers to a first 74HC595 8-bit register using its “Data Input,” “Clock” and “Latch” lines. Once the register receives a total of 8 bits (1 byte), it will overflow the data out through its “Output” line which can be connected to the “Data Input” of another register.

We toggle the “Clock” to signal to the registers to record the value of the data line (1 or 0). We do that for each of the bits of the two bytes we need sent for each display. Finally, we have the ATtiny85 toggle the “Latch” to let the registers know when the transmission is complete. They then lock the 8 output lines (QA to QH) to high or low depending on what they recorded. These lines are connected to the individual LEDs on the 7-segment LED displays.

I found a great example of using the 74HC595 to drive multiple LED Displays here. I used that code to send the data as well as the byte arrays used to form the numbers on the LEDs. Since that project was using a common anode LED and my project uses a common cathode LED I had to flip the bits. In the code below, a one (1) value would drive the LED high (on) and a zero (0) would drive it low (off).

/* Set up 7-segment LED Binary Data

     |--A--|
     F     B
     |--G--|
     E     C
     |--D--|   H - Decimal

     0b00000000
       ABCDEFGH
  */  
  numArray[0] = 0b11111100; // 0 - Zero
  numArray[1] = 0b01100000; // 1 - One
  numArray[2] = 0b11011010; // 2 - Two
  numArray[3] = 0b11110010; // 3 - Three
  numArray[4] = 0b01100110; // 4 - Four
  numArray[5] = 0b10110110; // 5 - Five
  numArray[6] = 0b10111110; // 6 - Six
  numArray[7] = 0b11100000; // 7 - Seven
  numArray[8] = 0b11111110; // 8 - Eight
  numArray[9] = 0b11110110; // 9 - Nine
  numArray[10]= 0b00000000; // All Off

Circuit Schematic

Pulling it all together, here is a schematic I put together that combines the ATtiny85 with the two 74HC595 registers, two LED displays and the HC-SR04 ultrasonic sensor.

A Kicad schematic is included in this project and the schematic export is sown above. The circuit is powered with a steady 5V DC supply (e.g. USB adapter). The HC-SR04 is an entry level sensor and does suffer from some fluctuation. Logic in the code attempts to stabilize the measurement by making multiple readings.

List of Materials

1 x ATiny85 Microcontroller (DigiKey)
2 x 74HC595 8-bit Shift Register (DigiKey)
1 x HC-SR04 Ultrasonic Distance Sensor (DigiKey)
2 x 7-Segement LED Display CC (DigiKey)
16 x 220 Ohm Resistor
1 x 100uF Electrolytic Capacitor (DigiKey)
1 x 0.1uF Ceramic Capactior – (Amazon)

Code

The code for the project can be found on GitHub: https://github.com/jasonacox/UltrasonicDistanceDisplay

Imperial and SI Units

In Imperial unit mode, the code is written to display distances in inches (1 to 11) for distances less than 1 foot. Once the distance reaches 1 foot, it will show feet in decimal (1.0 to 9.9) until the distance reaches 10 feet when it will display in feet only (e.g. 10).

In SI unit mode, it will show centimeters for distances less than 1 meter (1 to 99, then it will show meters with decimal (1.0 to 9.9) until the distance reaches 10 meters and will continue to show meters only.

To toggle Units: Hold the distance to 4 (either unit) for ~4 seconds and it will toggle between units. Imperial mode will flash “in” and SI mode will flash “c”.

Sleep Feature

Sleep Mode: The code includes logic to turn off the display when there is no movement and power back on when movement is detected.

Prototype

April 4, 2020December 28, 2023

ATtiny85 Arduino Programming with Sparkfun Tiny Programmer on a Mac

This guide will help set up a Mac OS computer to program an ATtiny 85 using the USB Tiny AVR Programmer from Sparkfun and the Arduino IDE.

Required Items:

Sparkfun Tiny AVR Programmer (Sparkfun) – This is a handy USB based programmer for ATtiny microcontrollers. It is powered by an ATtiny84 that is set up as a USBtinyISP programmer. The board has an 8 pin socket to hold a ATtiny45/85 microcontroller that you want to program.
ATtiny 85 Microcontroller (Digikey) – The ATtiny85 is a low-power 8-bit microcontroller based on the AVR enhanced RISC architecture.
Arduino IDE (Download)
Mac computer (e.g. MacBook Pro) with OS 10.14 or later

I used the following steps to get the Sparkfun Tiny AVR Programmer working on my Mac. Hopefully this will be helpful for you as well. Your experience may vary.

Step 1: Install ATtiny85

Install the ATtiny 85 into the programmer. Make sure you orient the chip so that pin 1 (usually identified by a dot) is by the notch. Once this is installed, plug the USB into your computer. You will not see a light and Mac OS will not recognize it as a serial port (don’t worry).

Step 2: Set up Arduino IDE

Install the Arduino IDE software (Download) and navigate the menu Arduino -> Preferences and in the field for “Additional Board Manager URL” paste this link:

https://raw.githubusercontent.com/damellis/attiny/ide-1.6.x-boards-manager/package_damellis_attiny_index.json

Click “OK” to save and restart the Arduino IDE. Navigate the menu Tools -> Board -> Boards Manger and type “attiny” into the top search board and there will click on the “Install” button on the attiny board package.

Find the attiny board package and Install.

You should now see an entry for ATtiny in the Tools > Board menu. Select “ATtiny25/45/85”.

For “Processor” select the chip you are using, e.g. ATiny85.

For “Programmer” select “USBtinyISP“

For “Clock” unless you have an external crystal in your circuit, you should select “Internal” and 1 MHz seems to be fine for most projects.

Finish by clicking “Burn Bootloader“. You should see the LED on the programmer flash. If it doesn’t work, you may need to Quit the Arduino IDE and restart to try again.

Please note: On the Mac, you do NOT select a serial “Port”. The IDE will program the ATtiny through the USBtinyISP that is loaded on the Tiny AVR Programmer board.

Step 3: Program your ATtiny85

You can use the example blink test to make sure you can program your ATtiny85. You can use the built in blink test but you will need to change the LED_BUILTIN to be 0 (zero). You can also copy and past the following code:

void setup() {
  pinMode(0, OUTPUT);
}
void loop() {
  digitalWrite(0, HIGH);   
  delay(1000);                       
  digitalWrite(0, LOW); 
  delay(1000); 
}

Arduino 1.x IDE: Click the upload button (right arrow) or press Command-U.

Arduino 2.x IDE: Select Sketch > Upload Using Programmer or Shift-Command-U

Arduino 2.x IDE – Uses “Upload Using Programmer” or Shift-Cmd-U

Once uploaded, the built-in LED should start to flash.

Example “blink” program running on ATtiny85

The ATtiny85 has PWM (Pulse Width Modulation) outputs so you can use the analogWrite() function to adjust the brightness of the LED from 0 to 255. Here is an example that fades the LED.

/*
  Fade
  This example shows how to fade an LED on using the analogWrite()
  function.
  The analogWrite() function uses PWM, so if you want to change the pin you're
  using, be sure to use another PWM capable pin. On most Arduino, the PWM pins
  are identified with a "~" sign, like ~3, ~5, ~6, ~9, ~10 and ~11.
*/
int led = 0;           // the PWM pin the LED is attached to
int brightness = 0;    // how bright the LED is
int fadeAmount = 1;    // how many points to fade the LED by
void setup() {
  pinMode(led, OUTPUT);
}
void loop() {
  analogWrite(led, brightness);
  brightness = brightness + fadeAmount;
  // reverse the direction of the fading at the ends of the fade:
  if (brightness <= 0) {
     analogWrite(led, 0);   
     delay(1500);
     fadeAmount = -fadeAmount;
  }
  if(brightness >= 255) {
    fadeAmount = -fadeAmount;
  }
  delay(10);
}

References

This was tested on Arduino 1.x and 2.x IDEs, on an Intel i7 based Apple MacBook Pro and on an M2 based MacBook Air using an USB-C to A adapter.

High-low tech: Programming an ATtiny w/ Arduino 1.6 (or 1.0) – http://highlowtech.org/?p=1695
Instructables: Program an ATtiny With Arduino – https://www.instructables.com/id/Program-an-ATtiny-with-Arduino/
Getting started with Atmel ATtiny85 (AVR Programming) – https://electronut.in/getting-started-with-attiny85-avr-programming/
Programming with AVRdude – https://learn.adafruit.com/introducing-trinket/programming-with-avrdude
Crosspack for AVR Development – https://www.obdev.at/products/crosspack/index.html
How to Program an Attiny85 From an Arduino Uno – https://www.instructables.com/id/How-to-Program-an-Attiny85-From-an-Arduino-Uno/
Programming the ‘AtTiny85’ With the ‘Tiny AVR Programmer’ and Supplemented ‘Arduino IDE’ – https://www.instructables.com/id/Programming-an-Atmel-AtTiny85-using-Arduino-IDE-an/

March 30, 2020June 22, 2020

Solar Powered WiFi Weather Station

I’ve always wanted to add a backyard weather station to help record not just temperature data, but humidity, pressure, rainfall, wind speed and UV levels. My recent experiments introduced me to the ESP8266 NodeMCU, a low-cost microcontroller with embedded WiFi. I just needed to add a solar cell, a battery, a sensor and an enclosure.

Solar Power

I found a 2.5W 5V/500mAh solar cell (from Amazon) and a 3.7V 3000mAh rechargeable Li-ion battery pack (Amazon). After some research (see here), I added a TP4056 charger module (Amazon) that regulates the charging and protects the battery from overcharge.

Solar cell and battery charging circuit. — Solar Cell + Battery Power Supply

I added a 0.1uF ceramic capacitor and 100uF electrolytic capacitor to smooth the output voltage. I used a simple 3.3v voltage regulator (DigiKey) to feed the 3.3v bus for the ESP8266 and sensors.

Monitoring the voltage coming from the solar cell and/or battery would help determine if the system is getting enough power during the day to keep the system running at night. The ESP8266 has an analog input (A0) that can be used to determine the output voltage but it can only handle up to 3.3v. By using a simple 2 resistor divider circuit (see right) I could monitor the voltage and apply a multiplier to get to the actual voltage I measured with a multimeter. In this case, the A0 pin was reporting 907 when the multimeter was showing 4.69v so I used 4.69 / 907.0 and further sampled other readings to ensure I had the correct value.

Voltage Charge and Discharge over 4 Days

Circuit Design

The sensors I wanted to add included a BME280 pressure and humidity sensor, a one-wire DS18B20 temperature sensor and a 2N2222 transistor powered rain detector. I put the circuit together using a simple breadboard and started on the code.

Using the free open source KiCad electronic design software, I build a schematic drawing to help build the final non-breadboarded product.

Schematic - ESP8266 Solar Powered Weather Station — Schematic – ESP8266 Solar Powered Weather Station

Getting Started with Arduino IDE and ESP8266

The ESP8266 NodeMCU has a USB port that allows the microcontroller to be easily powered and programmed with the Arduino IDE . However, it is not as easy to set up and use as an Arduino device. I found out that you will need to install a driver to see the device on my MacBook (see here for MacOS instructions and download the USB to UART Bridge VCP Drivers here). Once the driver is installed, the Arduino IDE needs to be set up to manage the NodeMCU. The ESP8266 I purchased came with some instructions:

Instruction & Steps of How to use:
1. Download and Install the Arduino IDE (download here)
2. Set up your Arduino IDE as: Go to File->Preferences and copy the URL below to get the ESP board manager extensions: http://arduino.esp8266.com/stable/package_esp8266com_index.json
3. Go to Tools > Board > Board Manager> Type “esp8266” and download the Community esp8266 and install.
4. Set up your chip as:
Tools -> Board -> NodeMCU 1.0 (ESP-12E Module)
Tools -> Flash Size -> 4M (3M SPIFFS)
Tools -> CPU Frequency -> 80 Mhz
Tools -> Upload Speed -> 921600
Tools -> Port -> (whatever it is)
5. In Arduino IDE, look for the old fashioned Blink program. Load, compile and upload. Go to FILE> EXAMPLES> ESP8266> BLINK

Code

Once I had the ESP8266 connected, I could start creating the code. The code is available here: https://github.com/jasonacox/WeatherStationWiFi

Rain Sensor

Using a simple NPN transistor, you can detect the presence of water. I wanted to detect rain which mean that I needed to add a couple of electrodes connected to that transistor (for detection) and our power supply. Water allows a small amount of current to pass through it to detect water, you will need to amplify it, hence the need for the transistor which turns a low current into a switch to a much larger current. The ESP8266 digital inputs can see the switched power from the transistor and can indicate water has been detected.

Wind Speed Sensor with an Anemometer

An anemometer is a device used to catch the wind and record its speed.

I found a 3D model on https://www.thingiverse.com/thing:2559929

More to come…

Installation

July 3, 2017November 3, 2023

Home Automation – SentryPi

Who left the garage door open?

We have a full house with a lot of activity and visitors. There have been several times when the garage door is left open for extended periods of time. While our Christmas decorations and paint supplies may not be a treasure most would be thieves would desire, it is still not the most comforting thing to think about leaving the garage open for all passerby to see. I often thought it would be great to have a way to notify whoever is in the house that the garage is open.

Phase 1 – LED Indicator

I decided that my first step would be to design a way to detect “door open” by providing a simple indicator light. I explored a few optical ways to do this (light beam, camera, reflectors) but quickly pivoted my approach when I found some unused microswitches.

I found a good place to detect “closed” on the main track. I thought about piggybacking on the garage opener sensors but dismissed that as I didn’t want to risk an undesirable interaction with the opener and more importantly, I wanted to have the detection work even if power to the opener was interrupted.

This required that I build a bracket to mount the switch to and a ramp plate to compress the switch when the door was in the down position.

I used an aluminum sheet, cut with sheet metal snips, bent and drilled holes to mount the microswitch and eventually attach it to the garage door track. It took a few tries to get the right fit and right placement of the micro switch.

My first attempt destroyed the microswitch after a few uses. The garage door track sled has a straight edge that collides with the microswitch roller. It created too much force on the small roller and eventually popped it loose. To help with that, I added an aluminum ramp to the sled so that the microswitch roller would gently rise as the sled entered the “closed” position.

I decided to make the “door open” state be the closed circuit condition so that phase 1 of the project could start as a simple LED circuit indicator.

I attached the switch and drilled some pilot holes and mounted the bracket to the garage door track right above the sled when the door is in the closed position.

I added a 9V battery, a 470 ohm resister and a red LED to the circuit. To complete this phase, I ran the wire from the garage to our entry hall and mounted an LED and housing above the HVAC controls. Now we can all see the brilliant red LED glowing when the garage door is open. That covers some of our use cases but I also want a more proactive notification. Now on to phase 2…

Phase 2 – Raspberry Pi – Home Automation Sentry

Now that I have a working “door closed” sensor and indicator, I am ready to add the proactive home automation component, specifically the Raspberry Pi (RPI). It just so happens that I have a spare RPI Model 3 that needed a project, and I wanted to experiment with AWS IoT services.

I used the RPI to detect the state of the switch. To do that, I will need to wire the circuit into the RPI’sGPIO headers. I decided to use GPIO Pin 23 and the adjacent ground (GND) pin.

Here is the code that is used to detect the closed circuit (indicating an open door):

#!/usr/bin/python

##  
## Garage Door Sentry - RPI script to monitor door
##  

## load libraries
import RPi.GPIO as io 
import time 

print "Garage Door Sentry\n\n"

## set GPIO mode to BCM - allows us to use GPIO number instead of pin number
io.setmode(io.BCM)

## set GPIO pin to use

door_pin = 23
print "Sentry Activated - Watching: GPIO 23"

## use the built-in "pull-up" resistor
io.setup(door_pin, io.IN, pull_up_down=io.PUD_UP)  # activate input

## States for door: 0=closed, 1=open, 2=init
door=2
## infinite loop
while True:
    ## if switch is open
    if (io.input(door_pin)==True and door!=0):
        door=0 
        print "Door closed"
        # do some action
    ## if switch is closed 
    if (io.input(door_pin)==False and door!=1):
        door=1 
        print "Door open"
        # do some action
    time.sleep(1) # 1 second wait

The next step was to connect to AWS IoT to record this sensor data and send alert messages to my phone.

The following will help you set up your Raspbery Pi as a platform to install the SentryPi scripts.

Required:

Raspberry Pi – B+, 2 or 3
Wifi Dongle or Network Cable configured
SD card (Recommend: 16GB or larger)
AWS Account (IoT, DynamoDB)

Read the details on this GitHub Project: https://github.com/jasonacox/SentryPi

The project describes how I added these additional features:

Sentry Alert – Send a text message to contacts when an alert condition is reached.
Dashboard – Provide an automation dashboard for realtime status.
Other Sensor Data:
- Temperature Sensors
- Barometric Pressure Sensor
- Humidity Sensor
- Motion Sensor

To set up a web based dashboard, I decide to use static HTML, CSS and JS (jQuery, Chart.js and the AWS JavaScript SDK) so it can be hosted on a simple S3 bucket, a web server, or the RPi itself. See here for the code.

December 26, 2013December 26, 2013

Arduino – Home Automation

A friend of mine at work has crafted a tiny HTTP web server in C to run on the Arduino Uno to provide an interface to manipulate external devices (imagine turning on lights, adjusting the thermostat or even opening the garage door).

References

Arduino: http://arduino.cc

December 25, 2013December 30, 2013

Raspberry Pi – AirPiano

Wouldn’t it be cool if you could control your MIDI equipped digital piano from your iPhone? Imagine a player piano capable of jukebox queuing up MIDI or Audio files and playing them in order. That was my goal! RPI to the rescue.

Required Ingredients:

Raspberry Pi – Model B, 512MB RAM, 16GB SD Card, Raspbian Linux, Apple 12W USB Power Adapter, USB WiFi Dongle
USB MIDI Digital Device (e.g. Yamaha Clavinova CLP-440 with USB MIDI port and RCA L+R Audio Inputs)
Software: Apache HTTP Server, PHP, MySQL, (Nice to have: Netatalk file server, Shairport AirPlay server)

Instructions:

My original thought was to turn the Yamaha speakers into a AirPlay device for our many iOS devices. It’s nice to pipe in background tunes without having to hook up a device. AirPlay is great way to do that but I didn’t want to spend $100+ to be able to do that. The Raspberry Pi is more than capable of doing this. I found an extremely helpful blog post here: http://www.raywenderlich.com/44918/raspberry-pi-airplay-tutorial

NOTE: Power is a big issue for the Raspberry Pi. If you are using a WiFi dongle or any other USB device, I recommend making sure your power supply has enough kick to keep the RPI going. I started out with a microUSB adapter that advertised 700mA but performance became very unstable, especially under load. I switched to a 12W Apple adapter that I had handy and the problems disappeared. The RPI FAQ recommends 1.2A (1200mA).

Setup for AirPiano – MIDI Control

The Project Code: https://github.com/jasonacox/raspberrypi

MySQL: Database ‘piano’ – see piano.sql file

Dequeue Service: Run the cron.sh script to have the RPI scan for new midi or wave files to play. Run it with:

bash -x cron.sh 0<&- 1>/dev/null 2>/dev/null &

Apache: Install apache http with mod_php and mysql support

Website Code: Install index.php, setup.php and the folder.png files into the document root of your webserver. Upload the MIDI (*.mid) and WAVE (*.wav) files to this location. Be sure to update $globalBase in setup.php to the folder where these files are located.

AirPlay via Raspberry Pi

Adam Burkepile has the best tutorial I’ve found on how to set up a RPI for AirPlay:

http://www.raywenderlich.com/44918/raspberry-pi-airplay-tutorial

Apple Share (AFP) Server via Raspberry Pi

The RPI is great for a tiny file server! At the least, having it run an AFP server will allow quick drag and drop transfer from your Macs. A Samba service for Windows shares is easy to set up as well.

sudo apt-get install netatalk

Yes, it is that easy. Finder will now show your Raspberry Pi under “shared” along with any other local network shares:

September 14, 2009February 22, 2024

Simple LED Flasher using Transistors

Simple LED Flasher Project

I wanted to put together a simple two LED flasher circuit that would use the fewest parts and low power. My first project of this type used the NE555 timer IC but besides the chip, it requires more power than what I would like to use. Using a couple low-power NPN transistors, the circuit should be able to run for hours on a 9v battery.

The Circuit

I decided to use two 2N3904 transistors (a low power NPN transistor). This design uses only 10 components but I added additional resistor to inline with the power source. It could be removed and the other resistors adjusted to lower the power.

I used a free copy of LTSpice from Linear Technology to create the circuit (most SPICE packages do not have LED components for some reason) – you can download it here: http://www.linear.com/designtools/software/ltspice.jsp

Which LED will light first?

The Breadboard

I assembled the circuit using a low cost breadboard I picked up at Fry’s Electronics. Using a breadboard allowed me to play around with different components, especially the capacitors and resistors to tweak the flash rate and brightness.

Single LED Flasher

The simplest single LED Flasher circuit I have found uses a single transistor (NPN), 2 resistors and 1 capacitor. This circuit uses the transistor as a Negistor using the NDR (negative differential resistance) effect. The transitor will block current until the voltage threshold charging on C1 reach something close to 9v, at which point the voltage will become large enough to get the emitter-base junction to avelanche and drain the current through the LED.

Click here for the video:
http://jasonacox.com/images/IMG_2022.MOV

Reference

http://wild-bohemian.com/electronics/flasher.html

http://en.wikipedia.org/wiki/2N3904

http://www.linear.com/designtools/software/ (LTspice – Nice circuit design tool based on Spice)

http://jlnlabs.online.fr/cnr/negosc.htm

http://www.cappels.org/dproj/simplest_LED_flasher/Simplest_LED_Flasher_Circuit.html