Clever engineering creates rock-bottom component tester

-August 15, 2014

While this sub-$20 board may not gain pride of place in your T&M rack, it's a fine tool for hobbyist and pro alike, and demonstrates the power of clever design.

Recently, while thumbing through eBay, I stumbled upon what appeared to be a magical everything component tester, for under $20. Always hungry to try new gizmos, I couldn't resist its charms, and placed my order with this seller, located in Shenzhen, China (there are other sellers too).

I normally wouldn't risk even $20 on such a toyish object, but this one inspired some confidence. The voluminous screen shots and the good seller rating were cause for some hope. And (spoiler alert), I wasn't disappointed. This is a really nice little design.

The board is billed as being able to test almost anything you might care to throw at it; and it does. Resistors, capacitors, and of course inductors. The ESR of inductors and some capacitors is also displayed, though, in the only failing I've found so far, capacitor ESR seems a bit flaky. You can even throw two resistors (or a pot) across the board's three test terminals, and both values will be displayed.

The very first part I tested after my board arrived was an unknown transistor, and the gain and Vbe both seemed improbably high. Whoa, it's a Darlington! That made for an interesting inaugural test! I tried a few more bipolars. Then, a JFET. Then a MOSFET. All parts were recognized, and basic FET parameters displayed. Impressive. Then, a wicked thought entered my mind.

I plugged in a very rare type of FET: a depletion mode MOSFET – one that is on at zero gate voltage. Colour me more impressed. The part was recognized too.

I was in for another surprise when I plugged a random LED from my parts bin into the tester. I pushed the test button, and the LED flashed red. Then it flashed green! What? I had inadvertently plugged in a two-leaded parallel pair LED. The board recognized both diodes, displaying Vf for each. Flashy.

It took some effort to find the origin of this design, an open-source project by Markus Frejek. If German isn't your thing, view the Google-translated page.

What contributes to the cleverness of this design is not only its versatility at recognizing components, regardless of how they're plugged in, but the fact that the business end of the circuit comprises one AVR microcontroller and six resistors. I'll say that again: one micro, and a few resistors. Markus must have had a ball coding this thing up!

So, do you think this is a cool bit of kit? Got any other examples of similarly clever design?

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