Posted on Oct 30, 2012

The pitch of the tone is dependent upon the resistance under test. The tester will respond to resistances of hundreds of kilohms, yet it is possible to distinguish differences of just tens of ohms in low-resistance circuits. Q1 and Q2 form a multivibrator, the frequency of which is influenced by the resistance between the test points. The output stage, Q3 and Q4, will drive a small loudspeaker or a telephone earpiece.

Click here to download the full size of the above Circuit.

The unit is powered by a 3-V battery, and draws very little current when not in use.

Leave Comment

characters left:

New Circuits



Popular Circuits

AIU - Analog Interface Unit
White LEDs Flashlight
Interface multiple keys with one wire and save pins of MCU
Sense automobile high-side current with discrete components
Power amplifier for Loudspeaker 6.5W 8R circuit
Universal AC Motor Speed Controller Kit
Sinewave Oscillator
A Low-Frequency Crystal Controlled Oscillator
Application circuit temperature sensor
Factory secondary low-voltage distribution electrical panel wiring diagram
High Power Full Bridge Flyback Driver circuit