Hacklet 104 – Test Equipment Projects

Hardware hackers love their test equipment. There are entire forums dedicated to talking about multimeters, oscilloscopes, signal generators, and other common bench tools. At times it seems we spend more time talking about our tools than actually using them. For some, off the shelf equipment is never quite good enough. These hackers, makers and engineers design and build their own test equipment. This week’s Hacklet is dedicated to some of the best test equipment projects on Hackaday.io!

test-tool-1We start with [Roman] and Handheld Electronic Test And Measurement Lab. [Roman] travels a lot, and often needs to bring a lab’s worth of tools with him. After suffering through several ‘random’ searches, he decided to design a simple tool that would cut down his packing, and not get him strip searched. The handheld lab packs a multimeter, low-frequency oscilloscope, data logger, waveform generator, and several other tools into a small package. The tool can be connected to a PC to display data and update settings. The on-board PIC24 handles all the hard work of taking measurements. Some careful analog design gives this tool 10 megohm of input impedance.

test-2Next up is [Jaromir Sukuba] with 10$ curve tracer. The only way to find out of that a transistor or diode really works as well as the data sheet suggests is to pull out your semiconductor curve tracer. Curve tracers are also perfect for matching transistors for projects like analog synthesizers. [Jaromir] built this quick and dirty tracer over the course of just two evenings. A dsPIC microcontroller runs the show, generating an IV curve by sending pulses through the device under test. Once the curve has been traced, the PIC displays the results on a TFT LCD module. The tracer is a bit limited with a max of 35V at 0.5 amps. Knowing [Jaromir] though, extending the range would only take another evening or two of work.

vlabtoolNext we have [Jithin] with A Versatile Labtool. This tool can do just about everything you could want – all in one box. From oscilloscope to frequency counter to multimeter to current source, and much more. Much like [Roman] up above, [Jithin] chose a Microchip PIC24 MCU as processing heart of his design. The Versatile Labtool connects to a PC via USB. If you’re not close to your PC, an ESP8266 module allows the unit to connect over WiFi. A PC isn’t required though. The on-board OLED is always available for quick measurements.

emtFinally we have [ZaidPirwani] with Engineer’s Multi Tool, his entry in the 2015 Hackaday Prize. [Zaid] started with the popular transistor tester codebase. He ported the code to his own hardware, an Arduino Nano and Nokia LCD. Making the port function required quite a bit more work than [Zaid] expected. He ended up going with a fresh repository and adding a bit of code at a time. Once everything was working, [Zaid] verified that his hardware design operated as expected with a good old-fashioned multimeter. Now that everything is working, [Zaid] is just about out of space on the little ATmega328. Next stop is a Teensy 3.2!


A special thank you goes out to [Jaromir Sukuba] for suggesting test equipment as the theme for this week’s Hacklet. You can find his projects and more on the new test equipment project list! If I missed your project, or if you have a suggestion for a future Hacklet theme, don’t be shy! Drop me a message on Hackaday.io. That’s it for this week’s Hacklet. As always, see you next week. Same hack time, same hack channel, bringing you the best of Hackaday.io!

Poor Man’s Time Domain Reflectometer

A time domain reflectometer, or TDR, is an essential piece of test gear when working on long cables. The idea is simple: send a pulse down the cable and listen for the reflection from the far end. The catch is that pesky universal constant, the speed of light.

The reason the speed of light is an issue is that, in a traditional system, the pulse needs to be complete before the reflection. Also, time is resolution, so a 1 GHz sampling rate provides a resolution of about 10 centimeters. [Krampmeier] has a different design. He sends variable length pulses and measures the overlap between the outgoing and reflected pulses. The approach allows a much simpler design compared to the traditional method.

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Build Yourself an Awesome Modular Power Supply

You may think you’ve built a power supply for your bench. Heck, we all do. But until you check out [Denis]’s bench power supply build, you may not even know what you’re missing.

[Denis]’s design is nearly entirely modular and targeted to the intermediate builder. It’s built on easily available parts and through-hole components. It’s got an Arduino running as the brains, so you’re going to be able to hack on the code when you feel like tweaking it. But easy doesn’t mean light on features. Let’s walk through the build together.


It starts off with a pre-regulator: a switching MOSFET that gets the voltage down to just a couple volts above the target value. Then it’s off to the post-regulator that includes all of the fine adjustments, the DAC and ADC interfacing to the microcontroller, and some fancy features like a “down-programmer” that turns the output off extra quickly.

On the user end of things, [Denis] made a very sleek board that incorporates a TFT touchscreen for the controls, Arduino connections, and the obligatory banana plug outputs. There’s opto-isolation on the SPI bus, a real-time clock, and a bunch more goodies on board. He’s in his third revision of this module, and that level of refinement shows. It’s even SCPI compliant, meaning you can control remotely using an industry-standard protocol.

So what would you do with a ridiculously fancy power supply under microcontroller control? Test out battery charging algorithms? Program test routines to see how your devices will work as their batteries drain out? We have no idea, but we know we want one!

You Can Learn a Lot from a Dummy (Load)

If you work on RF circuits–even if you aren’t a ham radio operator–you ought to have a dummy load. A dummy load is a non-radiative “antenna” with known impedance that you can use to test your RF circuit without radiating. For radio work, you usually just need a 50-ohm resistor that is non-inductive (at least at the frequencies you are interested in) and that can dissipate the amount of power you’ll expect it to handle (at least for a short time). [VO1PWF] wanted a dummy load and built his own.
CantennaThe Cantenna (not the Pringle’s kind; see left) was a famous dummy load design when Heathkit was in business. It was a single carbon rod immersed in a paint can full transformer oil (which we now know was full of dangerous PCBs; and we don’t mean printed circuit boards). [VO1PWF’s] design is a little more practical, using some resistors in parallel (20 1K resistors), a plastic pipe housing, and mineral oil to keep it all cool.

The reason for the parallel resistors is to maximize the power handling capability. The resistors are 3W units, so the dummy load–in theory–can handle 60 watts. Often, high power resistors are wire wound and thus have a good bit of parasitic inductance that makes the dummy load reactive (not a good thing since that makes the load impedance vary by frequency). They do make non-inductive wire wound resistors, but these aren’t truly non-inductive. The wire winds in two different directions, so the inductance tends to cancel out. We wouldn’t trust them to be a pure resistance in a high-power dummy load design.

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The Grid Dip Meter: Forgotten Instrument

It used to be a major rite of passage for a hardware hacker to acquire an oscilloscope. Until recently, new instruments were rarely in normal people’s budgets, so you probably made do with a used scope. Now, there are lots of inexpensive options, especially if you include low-end PC scopes and “scope meters.” Digital meters are also now inexpensive (often free at some major stores), along with signal generators, frequency counters, and even logic analyzers.

But there is one piece of test equipment you don’t see as often as you used to and its a shame, because it is a very versatile piece of kit. Admittedly, if you aren’t doing wireless work, it might not be high on your wish list, but if you do anything with RF, it is not only a versatile tool, but a good value, too. What’s it called? That depends. Historically, they went by the name “Grid Dip Oscillator” or GDO. Sometimes you’d hear it called a “Grid Dip Meter” instead. However, modern versions don’t have tubes (and, thus, no grid) so sometimes you hear them now called dip meters or maybe just dippers.

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The Junk Bins of Akihabara

Akihabara, Tokyo has transformed over the years. In its present form Akihabara emerged from the ruins of a devastated Tokyo after World War 2 when the entire district was burnt to the ground. The area was rebuilt in the shadow of the Akiba Jinja (dedicated to the god of fire prevention), and a new breed of street vendors began to appear. Huddling under the protection of railway bridges, and dealing mostly in Black market radio parts, these vendors set a new tone to what would become Japan’s “Electric Town”. And as Japanese manufacturing prowess grew so too did Akihabara.

Maids touting for business

Now of course Akihabara is also home to Otaku culture, and is perhaps best known in this regard for its maid cafes. Streets are littered with maids touting their cafes, somewhat incongruously among computer outlets and precision tooling stores.

My interests however lie squarely in Akihabara’s glorious junk bins. Of all places I think I’m happiest  digging through this mass of discarded technology from Japan’s manufacturing past.

A tour through the junks bins is like an archaeological dig. And in this article I will present some recent finds, and ponder on their relevance to Japanese manufacturing.

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VirtualBench Tear Down

What do you get when you cross a mixed-signal oscilloscope, a function generator, a multimeter, a power supply, and some programmable digital I/O in a box? Sounds like the set up to a very geeky joke, but it is actually National Instrument’s VirtualBench product. [Shahriar] has one and wanted to know what was inside, so he did a tear down.

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