Month: September 2009

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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

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The Samsung B630 LCD TV

The Amazing Samsung B630 LCD TV

On 6/20/09, we purchased a Samsung B630 40″ LCD TV.  The B630 has an amazing picture.  The 120Hz and high contrast features make this 1080p LCD monitor simply a delight.   The unit comes with 4 HDMI inputs as well as two standard A/V inputs for game consoles (great for the kid’s Wii and Playstatation2).  It also has a network port that pulls in news and weather feeds so you can hit an “info” button the remote and get semi-transparent overlay info boxes while watching your favorite show or movie.  Yes, this is more of a gee-whiz feature than actually useful though we have used it to check the local weather–its accuracy hasn’t been very impressive.

The set has an audio optical out.  I have this fed in to the Samsung DVD home theater system we purchased with the TV.  As expected, the sound is great but activating it always generates a pause while the TV and receiver sync up.  The set also has a USB port on the side that allows you to play media files (pictures, music and movies) from thumb drives and external hard drives.  It is a fantastic feature and providing you have a good quality USB drive, it will stream beautiful full 1080p video.

HDMI Problems

Just over 2 months after buying the unit, our cable suddenly stopped working on our new Samsung B630 LCD TV.  After some quick troubleshooting I discovered that it was only the HDMI-1 input that the cable box was using.  The Samsung DVD Player on the 2nd HDMI port worked fine and the Cable would work when plugged in to any of the other inputs.

I notice another strange behavior.  When the Cable and DVD cables were plugged in to HDMI-2 and HDMI-3, only one of the source inputs would work.  If you select 2 or 3, you would still see the same thing (the Cable which was plugged in to HDMI-3).   Moving things around to the other ports, I was able to do the same thing with the DVD.  This mean that we were not able to use the 2nd or 3rd ports to have HD signal from both the Cable and DVD player.   I eventually hooked up the component cables for the Cable box to the TV so that we could continue to view the up-conversion HD quality of our DVDs.

Samsung Support

The Sumsung website let’s you register and request repair for your Samsung products.  Besides the Samsung LCD TV and Home Theater System, we purchased  and registered our Samsung washer and dryer.   The website can be very frustrating at times.  It is slow and will frequently glitch.  At one point, I encountered a page that had a huge listing of products, complete with their serial numbers and details from other customers.  I didn’t drill in to see if it would present me with customer PII data, but clearly it shows that their web development team has work to do.

I did manage to report the HDMI problem via the website.  It does require that you upload the original receipt.  Unfortunately we had lost this (yes, not a good thing) but we had purchased this at Sears and the sears.com site will allow customers who used their Sears credit to view transaction receipts online.  This allowed me to copy/paste into a Word document and upload that to the Samsung site.    The site let us pick a date for the in-home repair and selected Monday.   We received a call the next morning from the repair team. After getting the details of the problem, they moved the schedule to Tuesday and said they would bring the components that they felt would fix the HDMI problem.

Repair Visit #1

The in-home repair technicians arrived and brought the mainboard replacement.  It looks like a small PC motherboard and is located in the lower left hand corner of the back of the TV, behind the connectors.  I took a picture as the techs were installing the new motherboard.

Back of Samsung B630 40

After installing the new motherboard, the TV flashed a red error message at the top of the set.  The tech attempted to reset the unit using various menu options (picture, firmware, etc.) but it would not clear.  He said that the new mainboard was defective and he would need to order a new one.  He re-installed the old mainboard.

Samsung B630 LCD TV Mainboard

Samsung B630 LCD TV Mainboard

After installing the old mainboard, the HMDI ports started working again!   I asked what they did and he said that it looks like the mainboard has a faulty connector that caused the outage.  He said that it does need to be replaced and they would order a new mainboard.  Until then, the HDMI may or may not stay working. Hopefully it will keep working until they return for their second visit.

It is interesting that Samsung would not quality check their mainboards before sending them out in to the field.  It seems to be a bit inefficient and if our old main-board had not mysteriously started working, it would be very frustrating for the customer.  But I will say that the repair technicians were very good.  They were friendly and quick.

Repair Visit #2

The technicians returned in two weeks to install the new mainboard.  Thankfully the HDMI port did not go out again before the second visit.

References

Samsung B630 LCD TV Manual

Samsung Website for B630 (firmware updates, FAQs, manuals, etc.)

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To Engineer is Human

To Engineer is Human: The Role of Failure in Successful Design by Henry Petroski

This is a great book to remind us of the purpose of engineering and the dangers we face when designing technical bridges (and physical ones) across the unknown.

Petroski wrote this in the early 80’s and the examples and illustrations are sometimes dated but still practical. I found the section on computers, “From slide rule to computer” to be particularly interesting.  His case still hold true for the faster/newer techno-driven culture of the 21st century.

We have come to be a society that is so quick to change that we have lost the benefits of one of mankind’s greatest tools–experience.   – Henry Petroski

Engineering is very dependant upon feedback for improvement.  The goal of providing a design solution for the lowest cost will mean that materials, processes and other costly items will be minimized to achieve the most economical/efficient solution.  Unfortunately, there are things that we do not know about (the trite, “we don’t know about what we don’t know” phrase comes to mind) that can be or become significant issues in the design.  The Tacoma Narrows Bridge is a great example of this.

Engineering attempts to introduce “safety factors” into the design model to cover for the unknowns but this can often be inadequate, as was the case of the walkway collapse at the Kansas City Hyatt Regency Hotel.

Failures, while unfortunate and often deadly, should also be opportunities for improvement.  Petroski argues that it is important that details of failures be broadcast to provide corrective feedback to all engineers so that future designs will build on these learnings.

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GeForce FX 5200 Problems

I have a e-Geforce FX 5200, 128MB, DDR, AGP Video Controller (p/n 128-A8-N303-L2).  We started having video glitches (blue screens, static and bad lagency on video games).  I took out the controller and noticed that 3 of the capactiors had popped.  Two are FZ72 1000 16V caps and one is a FZ75 1000 6.3V.