Fox and Hound

640px-Two_Vulpes_vulpes_pupsNo, not an article on QRP fox hunts (which I miss, being a bit out of range), but a construction project to make a pair of devices for tracing down wiring. The fox sends a tone down a wire and the hound sniffs around until it finds the right wire by detecting the tone. I found some commercial versions online at a reasonable price, but there isn’t much to these devices, so I figured I should be able to put them together from parts lying around. In what has to be one of the few examples of truth in advertising still to be found on the web, I came across neat circuits for these devices on

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Variable Power Supply

boxedUpI’ve been focusing on power supplies and related equipment lately because I don’t have a lot of bench gear. On one hand, I would like to build equipment from scratch, but on the other, it would be crazy not to look at some of the building block modules available on eBay and other outlets. I could not beat these prices, even if I built just about entirely from scrap. Using modules rather than homebrewing down to the metal seems like cheating, but it not only saves time and money, but often yields better performance and miniaturization.

So, this project consists of building a bench top power supply from three modules: a switching power supply that puts out a constant voltage, a DC/DC converter, and a combined voltmeter/ammeter. The combination is based on a youtube video by GreatScott that made use of a cheap DC/DC converter based on the LTC3780 that is being sold by various vendors  at a bargain price on eBay. Some of the same vendors are also selling a red and blue volt/ammeter. There are a few variations of the meter, I selected one rated for 100V and 10A and which did not require an external shunt resistor for current measurement.

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ATX Supply

supplyFrontRemember that ATX power supply that I fried last year? I replaced it with another mail-ordered supply and then it sat on the shelf long enough for me to get around to fixing it: a new regulator, some MOVs, a cap and the fuse, and it was ready for action — except I had no computer to install it in. I kind of doubt that I’ll build another tower form-factor computer, so I turned it into a high current bench power supply.

It has to be more than ten years since I’ve done this, and I believe the last time I didn’t even have an ATX supply. At that time, supplies needed a hefty load to get going and remain stable. I recall using a car headlight. Literally: an old-style (maybe halogen?) automotive headlight. I reviewed a couple videos on the subject to see what people were doing with more recent supplies and found one that I liked and more or less followed.

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Soft latch

I liked the circuit so much I made two of them. Here's front and back.
I liked the circuit so much I made two of them. Here’s front and back. The one on the left has an extra electrolytic cap; its addition did not affect the switching circuit at all.

Catching up on the bench back catalog: here’s a useful little module – a soft latch that isn’t finicky, works when you first plug it in, draws effectively no power when not changing states, and operates over a relatively wide range of input voltages. What’s not to like?

The basic idea is that mechanical switches, even simple toggles, are much more expensive than push buttons. It would be nice to be able to push a cheap push button and have it turn devices on and off. Some bad ways to do this would be to have the circuit twiddling its fingers, burning power, waiting for button presses – for example, having a microprocessor down stream of a voltage regulator idling until it detects a change in state on the pin connected to the push button. Sure, the microprocessor could be throttled down in some energy-saving mode and might only consume microamps, but the upstream voltage regulator would be consuming power, certainly true for linear regulators, and to a lesser extent for switchers.

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Back to the bench: 7 segment display

Three 4-digit displays: red, yellow, and green.
Three 4-digit displays: red, yellow, and green. Ew, shiny pads!

Since the SOTA genie escaped the bottle, the blog has leaned towards operation rather than bench work, but rest assured that projects have been percolating in the background. Here’s an update on a few of them: a custom LED display, a soft latch circuit, and a high-current converted ATX power supply. Let’s start with the LED Display.

For an upcoming project (actually, one that was moth-balled last June, stuck in a butter-cookie tin, and just recently again saw the light of day, followed by several days of pouring over notes and head scratching to remember where I had left off), I needed an LED display that would show voltage, amps, and power. Sure, you could figure the power out from the amps and volts, but I wanted it to change in real time to give me feedback while I make adjustments.

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Weller: The Final Chapter

Well, I hope it is the final chapter. I’ve written before about fixing and then learning that I hadn’t quite fixed my Weller WESD51 digital soldering iron. After much manipulation, I think I ended up cooking the PIC chip on the PC board, so I just ordered another board. Long story short: replacing the old board with a new one worked and I now have a functional solder station. I have some details below about where I ordered the replacement board and how I installed it in case anyone runs into a similar situation (or, given that cyclone season is again upon us with massive voltage fluctuations on the mains, in case my unit gets toasted again and I need to follow my own instructions).

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The Ginger Polygraph

The frequently lit red light indicates that our dog is lying.

My dog Ginger has a problem: she really likes food. That, coupled with her uncanny ability to convince family members that she has not been fed adds up to an overweight dog. She is not particularly sensitive about the subject and besides, she doesn’t read this blog (does anyone?) so I don’t think she’ll mind if I write about our attempt to find a technologically sound solution to her overeating, which is really a matter of our overfeeding her.

Ginger is supposed to get two scoops of dog food, one in the morning, one in the evening. Mornings, however, are chaotic. I get up and shower, and my wife adds food to the bowl. Then, while my wife is in the shower, Ginger whines and I figure she hasn’t eaten, so bowl number two. Often we’re out the door before the kids have emerged from their rooms, and at least one of them will take pity on Ginger, who clearly has not been fed at that point, and she gets her third bowl. Pretty much any time someone walks past her bowl, it seems that she hasn’t been fed. You would think we’d be on to her now, but there are times where in our rush to get out, we have made the mistake of each assuming the other one fed the dog. Ginger reminds us constantly of these rare occasions.

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Weller WESD51 Evil Football Taunt

Fooled again.
Fooled again.

You know how you never see negative results published? Well, here are some. Recently, I thought that I had used experimentation and logic to find a clever fix for my transiently functional solder station. For the entire day after I soldered in two capacitors, it worked beautifully. On, off. On, off. On, off. And every time I turned it on, the LED display lit up, the soldering iron got hot, and everything was peachy. Until this evening. I turned it on, finally hopeful that I had found an enduring fix and… no. Nothing. No LEDs. No heat. It mocks me.

Once again, with experience borne of many unproductive disassemblies, I tore the solder station apart and poked around. This time, poking the CLKOUT pin didn’t help. I clipped off the cap on the CLKIN. No help. I clipped off the other one, no help. I’m still getting power to the MPU, the oscillator is still oscillating. What gives? I didn’t keep at it long enough to see if it would randomly turn on again at some point.

You’ve won this round, Weller, but I’ll be in Europe next week — where they sell 230V Hakkos, and I’m just about ready to buy one.

Weller WESD51 Repair

wesd51My solder station, a WESD51 had become increasingly flaky over the last year – at times, it would fail to turn on. Flip the switch up and down a few times, and the digits would light up and the iron would heat; flip a few more and it would remain inert. Sometimes it would work immediately, sometimes it would just not turn on at all. Every time I took it apart, it would trick me by eventually working again, only to fail when reassembled. To compress months of annoyance into one sentence: I seem to have fixed it by soldering some capacitors onto the oscillator crystal. Note added after the fact: Nope this didn’t fix it. See next post for grousing.

Generally, I like Weller irons. I had used the analog version of this model (i.e., no LED digits, just a knob to set temperature) for a couple years. During that time, I had sunk some funds into buying a variety of tips from teeny screwdriver up to the broad chisel that I use for soldering coax plugs. So, when it came time to move overseas, I found a 230V version online and ordered it. I had considered just putting the US model on a transformer, but thought it better to have a model directly grounded through its plug. Continue reading “Weller WESD51 Repair”

Wifi for the Garage

A look inside the Linksys WRT54GS router used in this project.
A look inside the Linksys WRT54GS router used in this project.

Propagation has been abysmal, so it’s time to hang out in garage and work on projects. One catch: the garage PC gave up the ghost about a month ago. The Windows 7 computer had been functioning for a few months as a wifi repeater that let me use other wireless devices in the garage. Unfortunately, it looks like a power spike may have taken out the motherboard. I have retired that PC, and came up with a replacement: a linksys wrt54gs router reflashed with DD-WRT firmware and hardware modifications to add a cantenna.

Last week I made a video about putting up the hex beam, and now that I have the video editing software, I made one about the wifi repeater bridge project. Making video is somewhat addictive, so I think there are more on the way. I have a ways to go in terms of production quality – maybe Christmas will bring a better video-capable camera.

On the subject of videos, my home club, the Vienna Wireless Society, is now posting videos of presentations made at the club.