Multimeter 101

In the circuit I'm trying to reverse engineer I wanted to test change in the (static) resistance seen between ground and the mic input when the button is pressed.

When pressed, it measures as 0.7Ω -- which is the resistance of a ferrit bead inline with the mic input.

When closed, it measures ∞ on diode/bell, 20Ω & 2000Ω settings; but on the 20kΩ setting it measure 1.80 (sometimes 1.79 or 1.81 probably dependant on how good a contact I'm getting).

This confuses me. I should be seeing 1800(ish) when the range is set to 2000Ω?

What does this mean? Is my meter crap, or is there some other explanation?

Some lower end multimeters use different voltages on different resistance ranges. At lower voltages, it may not be enought to pass through a diode junction (hence infinity/open), At other resistance ranges, the voltage may be higher and manages to get over the diode junction and produce some readings.

How are you powering it?

Mike.

Pommie said:

How are you powering it?

Click to expand...

The circuit? I'm not.

The MM uses a pp9.

sagor1 said:

Some lower end multimeters use different voltages on different resistance ranges.

Click to expand...

If this is a digital multimeter that you are using, the meter will be trying to drive a a constant current through the "resistance" which it is trying to measure.
The voltage across the resistance will depend on the current and the value of the resistance.

If you have a different meter, you may get better results using that one.

It could be that the circuit that you are trying to measure is not amenable to measurement by a simple multimeter.

JimB