Saturday, March 14, 2015

Capacitance Meter and Transistor Tester

It's useful to have a way of measuring capacitors and doing quick checks on the pinout of transistors. In the case of capacitors, I find the labeling is often too small for me to read easily, or in the case of some SMD capacitors, not present at all. A nice, versatile design for such a device can be found here, in German. Now the last time I spoke any German was about the same time I started doing electronics, sometime in the 1970s. Fortunately English translations of the manual exist, at the SVN archive and in various other places. The most recent version I found was this one. You can find various sites around the web which describe it, including this slightly snippy evaluation of it.

There are many Chinese copies of the design. The one I got came as a kit from banggood. I ordered it from their US warehouse and it arrived within a week. There's a predrilled case available, but that was only available from China, so it will take longer to arrive. You can also get it already assembled from many places - just to a search on ebay. Assembling the kit was pretty straightforward. I have some tricks that help, like counting the pins on the IC socket as you solder them to avoid missing any out, and using a tiny piece of blu-tac to hold the sockets and power connector to the board while soldering them. The board looks well made and all the components were present, and the microcontroller that is at the heart of the design comes pre-programmed. There are two spacers for mounting the LCD on, and my one complaint is that it rests on top of a LED unless you get the LED really flat to the board or bend it slightly out of the way.

The manual describes and advanced menu and a calibration mode. They have to be selected at compile time, and I assume this wasn't done as neither function seems to work. According to the manual, a long press on the test button should put it into the advanced menu, and connecting the three test inputs together should get you calibration mode. Other than that, a few quick tests on known components all gave the right results.

I mentioned starting electronics in the 1970s (I stopped again around 1984 in favor of writing programs). My second ever project was a capacitance meter, from an article in either Electronics Today International or Everyday Electronics. It worked by generating a signal at a known frequency and then measuring the impedance of the capacitor. I never got it to work, due to a combination of my poor soldering technique and lack of knowledge about how to debug a circuit.

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