Electronics

Today I’m going to show a video on how to troubleshoot and repair a timer control. I will be sharing my evaluation of the problem and my final solution. Along the way I demonstrate three different methods on how to remove electronic components and I give some hints to make it easier. I show how to fix a fused relay and in just this blog posting, not the video, I also document how to test a bipolar junction transistor (BJT).

The three methods I cover are:
1) Manual desoldering pump at (adafruit.com)
2) 30 Watt Electric desoldering Tool at (amazon.com) or (elexp.com)
3) Solder wick at (adafruit.com)

If you don’t care to watch the video I will summarize below.

I have an exterior timer control that turns my Christmas lights on at dusk and off after 6 hours. I noticed they never turned off one day and thought I had left the timer control set to the ON position. But no, it was set to off 6 hours after dusk. I then set the selection switch to OFF but still it was on. I unplugged and plugged it back in but got the same problem. It was time to go to the electronics bench.

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Today I’m going to reviewing two types of Pomona test lead holders.

A representative from Farnell contacted me and asked if I wanted to review some products. I said, “Sure, free supplies for my lab!” Actually, I found out that anybody can sign up for their product “Road Test” program at Element14.com but not everyone is selected. Farnell is a European company and known as Element14 in Asia and Newark in America (online catalog). But they also have a nice online community site at Element14.com/Community where you can get to their “Store” for your region.

For the “Road Test” I chose to review some different test lead management hangers made by Pomona. I have quite the mess of jumpers, patch cables, DMM probes and oscilloscope probes hanging on my peg board behind my lab bench. That is not a good way to store these and they are very difficult to access on peg board.

I selected two sizes with two different mounting options for this review. The Pomona model 1508 with 14 slots at 0.21in (5.33mm) opening is great for jumpers, patch cable and test leads. The 1508 model needs to mount using screws.

<photo 1508>

I also got the Pomona model 4408M with 8 slots at 0.32in (8.13mm) opening with magnet mounting. The 4408M is nice for oscilloscope probes and larger items.

<photo 4408M>

I was quite disappointed to find that you lose two slots for the magnet mount because they just bend the outside prongs down and add stick on magnets. This magnetic option drops a model 4408 with 10 slots to a 4408M with only 8 slots. If I had known that I would have got the model 4408 and just added my own magnetic plate. The photo for 4408M at Neward.com is curretly wrong and shows the model 2708 without bent prongs.
The magnetic option was not strong enough for the thin metal in my garage door anyway so I bent the two extra prongs up and used the screw mounts.

You can fabricate your own test lead hangers but at these prices it just makes sense to buy.
1508 is $17.53 USD (at the time of writing this it is on sale for $12.46)
4408 is $14.65 USD  (at the time of writing this it is on sale for $10.43)
4408M with magnet mount is $32.13 USD  (at the time of writing this it is on sale for $23.46)

Here are the after shots of my lab. WOW these hangers sure helped clean things up and I have already found it much easier to find and select items.

I even found some lost jumpers and micro hooks. I thought they were gone forever but were just under the pile of cables hanging on my peg board. I will not be losing track of such items anymore!

I guess I will have to get one more 1508 because I have so many jumper cables. I may even get their biggest hanger model 2708 with 9 slots at 0.45in (11.43mm) opening for my PC power cords and wall warts.

Thanks for visiting.

On 11/28/2011 I was honored with being the “Featured Engineer” of the day at www.EEWeb.com. You can read the full Featured Engineer interview if you want to learn a few tidbits about my history and career in engineering.

G35 LED Christmas Light Review and Teardown

In this write up & video I review the “GE Color Effects” G35 multi colored LED Christmas lights 50 count. I will cover product details, hanging hints and show a teardown and give some links to great hacks at the end.

You get to pick from 14 sequence patterns using a wireless controller.  Hacking these lights using Arduino is already very popular so I will be linking to some good hack posts below. In a later video I will be trying some of the known hacks and some of my own.

Link to the GE product page for these lights

In the box you get the below:

40.8 feet of lights
50 lights spaced at 10 inches
50 rain gutter clips, 50 base clips
Radio controller with 14 light patters

CLICK TO READ ALL —>: (more…)

In this video episode I show how to replace solder tab rechargeable batteries in some very useful consumer products that would otherwise end up in a landfill. I use more common and cheaper none solder tab reachable batteries and show how to safely and effectively solder on the tabs.

First up was the solder tab type AA 1.2v Ni-Cd in my beard trimmer. I know, not the most attractive thing a man wants to see in his bathroom.

Then my programmable Christmas tree light timer which needed a coin cell 1.2v Ni-MH with PCB mounting tabs.

I noted in the video that it was interesting they were powering the timer controller using a bridge rectified AC to DC converter.  I was surprised to see this without the use of a step down transformer before the rectifier circuit.  Further research, I found this is quite common in consumer products that require less than 70mA and it can be done safely and cost effectively.  There are some pros and cons to this approach. If you want the full details with the math and picking the correct sized passive devices  you can review this nice article at Microship.com.  For the power conditioning circuit which is closes to what is in my timer see Fig.12 in the article.

I’m in a pinch and need to convert 120v AC to 12v DC to cool an electric motor. Not having much for supplies on a Sunday I pulled out the whiteboard and my calculator to devise a quick hack to power my 12v DC fan from the 120v AC mains running the electric motor. I needed only three components to create my DC power supply: a light bulb (40W), capacitor (470uF 80v), diode (1N4004) but in the video I used a salvaged diode from an old microwave oven.

In this video I share this simple hack and go into the math just enough so others can calculate the correct size light bulb for such a DC power supply hack if ever needed.

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Quick post on a simple repair that will save thousands of iClickers from the landfill.  I have had several iClickers handed to me to fix or just use for scrap.  Every one was fixable and it wasn’t even an electronic failure.

The failure comes under the category of “Design Failure”.  Product designers not knowing the manufacturing tolerances and component tolerances they are working with.  In the case of these wireless classroom participation voting remotes the failure is with the batteries not making good contact.

Below is a photo showing how the thick plastic is preventing the battery’s positive tip from reaching the contact.  For some batteries this is not a problem, for others you get intermittent on and off events and for Duracell you get zip.

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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.

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