Bob Parker Blue ESR Meter Build

I said I’d write when I had something else to break. Incorrect. I had something to build instead, and I’ll tell you all about it, but first let’s discuss . . .

The Theory:

ESR stands for equivalent series resistance. It’s a big term, but I’m going to try to make it simple. I don’t claim to fully understand it. Do your own research. Here goes. While every real capacitor, resistor, and inductor has its main property of capacitance, resistance, and inductance respectively, it also functions with slight values of the other properties additionally, though at far lower levels. For example, an inductor will mainly convert electrical current into a magnetic field, but it will also store a little energy by capacitance and waste a little energy by resistance as heat. An easy way to understand the way these “extra” properties of a real component behave in relation to the main effect is to think of them as being represented by other ideal components in series with the main one. Hence the term “equivalent series resistance”. ESR is the resistance in (for instance) a capacitor that is equivalent to a small ideal resistor used in series with an identical ideal capacitor. Got it? Let’s move on.

Then in case you haven’t noticed, we’re actually focusing on capacitors today. Electrolytic capacitors from the factory contain liquid electrolyte that helps store a charge. In brand-new condition, an electrolytic cap’s resistance (ESR) is measured with an AC charge usually at 100 kHz (somebody figured out that that works best for e-caps), and that’s the value it should keep for the cap’s lifespan. As the cap is used and abused, it degrades by means of the electrolytic fluid drying, and the ESR goes up accordingly, which screws with your circuit in ways I don’t yet understand. The kicker is that an electrolytic cap can dry out and go high-resistance while still retaining a measurable capacitance value that will appear to be within spec. So how can you tell if your cap has failed in this manner? Ya gotta have . . .

The Equipment:

Bob Parker Blue ESR Meter kit
The complete kit out of the box, plus a lovely set of 4mm parrot clips extra.

What we have here is a lovely product from Aussie electronics engineer Bob Parker. I chose this model because it’s the newer, handsomer version of the respected device in use by our man here.

This is basically a low-range Ohmmeter. It only displays .00 – 99 Ohms. Its important feature is its low-voltage, 100 kHz test signal for testing electrolytic capacitors in-circuit. The low voltage keeps most other components from activating and distorting the measurement on the cap or worse. The 100 kHz frequency matches most factory tests for easy comparison with a datasheet value. Beyond that, this thing is just really well-designed and assembled. The case is not only sturdy (it just feels good in your hand), but pretty. It only uses a single tact switch to power on and interact. The display is bright and easy to read. But I didn’t want to spend the extra $20 to have it assembled for me. I wanted to build it myself! So here is . . .

The Process:

Couldn’t be simpler! This PDF constitutes the manufacturer’s assembly instructions. I’m going to let the pictures do the talking here.

Killer helping hands tool
Killer helping hands tool
A Few Resistors In
Just a few resistors in and the fun is only beginning.
Resistors done, added caps and diodes. Note the tan-colored crystal in the lower left area.
Resistors done, added caps and diodes. Note the tan-colored 3.58 MHz crystal in the lower left area. It gets reduced to 100kHz somewhere in there.
Everything together with sockets for the ICs. I didn't feel up to soldering the ICs directly.
Everything together with sockets for the ICs. I didn’t feel up to soldering the ICs directly.

















The Outcome:


It worked first try! Pressing the top button once powers the unit on. Clipping the leads together and pressing the button again zeroes the meter to the resistance in the leads, and the meter powers off automatically. The manual details a calibration procedure using the the included 82 Ohm 1% tolerance carbon film resistor. With the unit out of the case, variable resistor 2 (the upper of the two dials with the phillips relief) can be adjusted until the display literally reads 82. Unfortunately, when I last tried it, adjusting the potentiometer had no effect. Not sure what’s up with that. But it seems to work and read fairly accurately. Someday I’ll take the time to learn.

While researching this article I came across a quote that was just too, too true.
“Three weeks in the lab will save you a day in the library every time” – R. Stanley Williams


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