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capacitance meter


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  • 3 weeks later...

:) re your capacitance meter project:
1. can this meter measure the "effective series resistance"?
Project Link: http://www.electronics-lab.com/projects/test/006/index.html

No, this circuit cannot measure ESR.
You can find circuits for this purpose if you search the internet. Some of them are offered as kits.
Some months ago(maybe 1 year or so) Elektor magazine published an article including all the schematic, PCB etc of an instrument that could measure ESR onle, not capacitance, but it had easy to find and no programmable components, so it was easy to build. I made one and I am very happy with it.
My advice is to build one. It is very helpfull in finding faulty electrolytic capacitors.

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  • 1 year later...

I took a look at this circuit and found it odd in a couple of ways. What is the purpose of the two diodes. It seems that one end of the capacitor in question is charged to 5.2volts and the other end swings from 0 to 5.5volts. While I understand discharge through the ammeter I don't understand why the circuit is structured the way it is and I don't understand the role of the two diodes.

In fact, I took a look at the voltage levels and it does not appear that there is discharge through the ammeter. I see charge when the output of the 555 goes low bringing the other side to 5.2 volts. But when the putput of the 555 goes high the maximum voltage that instantly appears at the other end of the capacitor is 5.5volts. With this voltage, how is either diode going to conduct. I really don't see it but I should keep an open mind.

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When the 555's output goes low, the cap charges through the upper diode and the resistor. The lower diode is reverse-biased.
When the 555's output goes high, the upper terminal of the cap is driven above the supply voltage due to its charge (see the meter's polarity?), the upper diode is reverse-biased and the cap discharges into the lower diode and the meter.

BTW, I think that the polarity of the 10uF cap across the meter is backwards. ::)

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Thanks Audioguru, that is something I need to suspect. I am not really comfortable when it comes to clamping but I believe your statement to be true if the thing works. Isn't the design a little bizzare. I would just expect something different from a capacitance meter. It seems like the circuit was just thrown together to appease the draw on the power supply. Could it really be possible that this is one of those circuits that happens to work modestly. I really appreciate you sticking out your neck on the clamping action but it seems reasonable to me.

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