ESR meter for less than £20?

[Yorkie]

Like David I built this one http://members.shaw.ca/swstuff/esrmeter.html and it was a nice little project and cost about £10 in total to make. Not only is it a very useful bit of equipment but you also have the satisfaction in knowing you built it yourself.

I refined the original circuit and PCB layout over time, based on feedback from others such as Josh & Rob, making it easier to build and adjust than the original design, and I know that scores of them have been built, as I've helped many people who've had trouble getting it to work. I've also built about 20 myself for friends, and they work first time if built with care. Even if all the parts are bought new, including the 50uA meter, (except for the case and PCB) it can be built for under ten pounds. It's a nice little project too, which soon earns its keep, and although a scope isn't essential, if one is to hand, the project is instructive as to what happens at various points in the circuit when the waveform is observed on the scope. Like almost all ESR meters, it works on the basis of an oscillator running at a frequency of about 100kHz (actual frequency unimprtant) being applied to a capacitor under test, with the results of the effective series resistance of the cap displayed on an expanded scale meter.

There isn't a reliable test for electrolytics other than an ESR meter, because if tested on a capacitance meter alone, the cap may look fine, but may still have a high ESR. Admittedly this is of limited interest in valve radios, whih generally only have two smoothing caps and perhaps a 25uF 25V cathode by-pass cap in the output stage, but its useful in transistor radios, TVs, and particularly switched mode PSUs, all of which use lots of small electrolytics which develop a high ESR as they dry out over time.

I wrote a very detailed post at the thread below - so detailed that it probably put off more people than it encouraged! However, it's bascially a very simple design - one IC of which one gate is used along with a resistor and capacitor for the oscillator circuit, the other five gates of the IC form a buffer/low pass filter, then the square wave is amplified by a 2N2222 transistor. Just a handful of components, all of which apart from the LED and on/off switch are mounted on the PCB. (see the pic of the completed PCB at the link to my posting below)

If any forum members do have a go at that project, and get stuck, I'll be happy to help in troubleshooting.

http://golbornevintageradio.co.uk/forum/thread-411.html

David.

I'll be interested to learn what the other 'cap wizard' jobby is like when it arrives - it seems a bargain on the face of things!