Electronics

This is Part 5. You may want to read (part1), (part2), (part3) & (part4) first.

Today I continue my rainy day power supply repair project. I have checked everything twice and even took a shot in the dark by replacing all the ICs on the board. I still don’t know why this circuit is not working. The power transistors on this board should supply a ground path for the motor when activated by a plus on their gates. The pulse is not appearing at the gates so I know at the heart of the problem the pulse width modulation chip (PWM) is not doing its job. I have replaced the PWM chip but that didn’t help.

In this video I dig a bit deeper using my oscilloscope to look at some select voltage signals going and coming from the PWM chip. I even bypass the PWM and inject a pulse train from my function generator to test the power conditioning and power transistors. I can’t simply replace the existing PWM chip with another manual controlled PWM chip because it currently uses current sense feedback as well as signals from adjacent control circuitry to not only start the plus train but also control its duty cycle. These are critical features for a treadmill or metal lathe motor control circuit in order to maintain a selected motor speed under load.

Just posted part 6 of 6 which is the final post.

This is a continuing post in a series about using the Adafruit.com bicycle spoke persistence of view board (SpokePOV). This is a great electronics kit that lets you draw amazing images like below from LEDs attached to your bicycle spokes. You can even do animations while you ride if you use 3 SpokePOV boards which is also sold as a kit.

You may want to first read (part 1 of 7) of this blog post series.

I was going to post the next 5 parts separately but decided to just combine parts 2 through 6 in this posting. Below is the list and you can scroll to see each section. There maybe a final separate 7th posting on creating a “Corrective Raiser image Board” (CRiB) board to correct a slight design flaw with Adafruit’s SpokePOV boards as noted in part 6 below.

Part 2: Mounting an adjustable magnet on the bike frame
Part 3: Building bench testing rig for SpokePOV
Part 4: Programming images and setting the SpokePOV board offsets
Part 5: Halloween image and video of SpokePOV in action
Part 6: Troubleshooting an image skew problem

Part 2: Mounting an adjustable magnet on the bike frame

The SpokePOV kit comes with a very strong magnet which is used to trigger the Hall Effect sensor on the board as the board rotates with the wheel. In the suggested configuration from Adafruit the magnet just sticks to the inside of the bike’s front fork. This is not optimal because the magnet will not be adjustable with respect to the board and the magnet could easily fall off or move when encountering a bump. You could epoxy the magnet to the frame at a selected height but then the tire could be difficult to remove.

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Tutorial using a Tripp-lite IS1000 isolation transformer.

1. What I bought for my tech bench.
2. Some models and prices of isolation transformers.
3. How to alter a public version into a tech version.
4. Helpful tips on using your oscilloscope safely with and without an isolation transformer.
5. How to be a little safer when working with high voltage live mains

These would be good tech isolation transformers that don’t need to be modified:
4.30A isolation transformer, 115/115VAC, 500VA
2.50A isolation transformer, 120VAC/120VAC, 300VA
1.25A isolation transformer, BK Precision BK1604A
0.43A isolation transformer, 115VAC, 50VA

A video on how to tune your own piano using an oscilloscope. I think it’s an interesting use of an oscilloscope!

This is a video post on how to take your laptop apart and fix a broken power jack. It also includes some useful DIY repair tips and tricks. This is a very common failure with laptops because users trip over the cords. You could score a nice laptop off EBay for under $50 with nothing more wrong with it than a power jack. This video will show you one simple way to fix such a problem.

This is Part 3.  You may want to read (part1) & (part2) first.

In this part I was going to probe the board to find where the signal was being lost for the controls. After mapping out all the connections and looking up the functionality of the ICs in the earlier postings I was confident I was going to track down the problem. I had the motor secured in my bench vise, the power supply and speed control board connected to the speed sensor feedback and mains 120v to a switch. When I turned on the 120v mains power I could smell something getting hot real fast. I had to work 30 second at a time and let the control board cool between tests. Something was not happy in the power supply! The heat was coming from a large 4watt 1.8K ohm resistor. I didn’t dare probe for more than 30 seconds because it was clearly getting too hot. But I pushed my luck too far (KA-BAM!).

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I was helping HeatSync Labs with their amateur high altitude balloon launch back on August 27th 2010. I finally got time to post the photos and the video. It was a great launch and recovery.

We launched the balloon at 8:04am and recovered it at 10:18am. Here is a link to the GPS tracking data from the balloon.
This flight tracking data may not be available, sorry.

Everything survived the landing. We landed in some farmland just off a dirt road and the transmitter worked the whole time so it was an easy recovery.

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I have a custom Arduino board project to share including bonus steps at the end on how to program a blank ATmega168 or ATmega328 with your Arduino sketch directly from the Arduino IDE environment using an USBTinyISP programmer from Adafruit.  

 I’m going to hack a Christmas photo frame I got a few years back when my son visited Santa Clause. The photo of him sitting on Santa’s knee came with a nice frame that had 5 LEDs that flashed when you turned it on.  It ran on two AAs and used a “chip-on-board” to control the flashing pattern of the LEDs.  

 The problem was that this thing flashed all 5 LEDs four times a second! We could never leave it on because it would drive you nuts.  Ever since I purchased it I have wanted to hack it so the lighting was not so annoying. This is going to be mostly a video posting but I will put in some “how to” notes, helpful links, photos, circuit and code so it will be more useful to you for adding such a hack to a project of your own.  

 Below is a video of me describing the problem and proposing the project.  A few things did change after the video but I will note the changes below.  

Below is the original board from the photo frame.  The “chip-on-board” is under the black blob.  

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(part 2 of 2)

You may want to read part 1 first.

The person whose Seagate micro USB drive I was trying to fix bought a second working unit from eBay for under $20 bucks.

Below are the two Seagate micro USB drives. One working unit from eBay the other not working and needing data recovery if possible.  The task? Switch the platters and hope the working unit will read the old disk.

Disassembling the new unit to get out the platter

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