555 audio ohmmeter circuit
This is a 555 audio ohmmeter circuit. Some times, we need to measure roughly the resistances only. In this we can know the resistances by the audio so also fast check.
This circuit will use the resistors that unknown value to compare with many the reference resistors.
In Figure 1 is the circuit we use IC-555 works as the frequency oscillator circuit. The IC1′s output of IC1 will drive the piezo speaker.
The circuit’s frequency will depends on the value of Rx (the unknown resistor) and can be calculated from…
In2 = 0.6931, All resistors have unit in “ohms” and the C2 has unit in “farad”
Then we put the unknown resistor into the RX. The circuit will generate the audio to the buzzer emit by frequency that we calculate above.
But how to compare various resistors, will easier calculation.
If Rx is zero the output frequency about 4,500 Hz and when Rx is infinitely value, the output frequency will be about 2 Hz.