'Instant' Resistor Measurer

Wed, 30 Aug 2023 00:00:00 +0000

This project is a little old, but now that I have some time, I thought it would be nice to write it up! The device has been serving me well for a few years now.

Being somewhat red/green color blind, I’ve always had trouble reading through-hole resistor color codes (though I often wonder if those with full color vision have it much easier - some resistor bands are so ‘muddy’!) I make do with labeled pouches holding my resistors, and a multimeter to double-check. The multimeter is so slow. Surely it shouldn’t take seconds to sense a resistor value!

For years I dreamt of making a faster resistor measuring device with an instant readout.

The ‘final straw’ that pushed me to actually do that was that I bought a beautiful old metal Akro-Mils cabinet¹ stuffed with old through-hole carbon composite resistors at the Silicon Valley Electronics Flea Market. The resistors were obviously sorted in the drawers at one time - but time and chaos had taken their mysterious toll, and they’d become pretty substantially mixed up.

I needed to sort these hundreds of resistors if I was to ever use them. With the multimeter, that would take for ever.

The ‘resistor measurer’ I built (call it an ohmmeter if you insist) works really well. It measures the value of a resistor fast enough to seem instant, and it optionally rounds to the nearest E24 or E96 value. I also designed and 3D-printed a benchtop case for it.

I’m quite pleased with the circuit I came up with to measure the resistance!

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Resistor Measurer on Jamie Montgomerie’s World Wide Web Log

'Instant' Resistor Measurer