Logic probe

Posted on Jan 11, 2013

Transistors Q1 and Q2 form a buffer, providing the probe with a reasonable input impedance. Q3 and Q4 form a level detecting circuit. As the voltage across the base-emitter junction of the Q3 rises above 0,6 V the transistor turns on thus turning on Q4 and lighting the red (high) LED. Q5 and Q6 perform the same function but for the green (low) LED. Ql, Q4, Q5 are all PNP general purpose silicon transistors (BC178 etc)

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

Q2, Q3, Q6 are all PNP general purpose silicon transistors (BC 108 etc) The threshold low is 0 V, and the threshold high is 2 V.

Leave Comment

characters left:

New Circuits



Popular Circuits

Commodore 64 Clock Circuits
high power regulator
Telephone call meter using calculator & COB
Advanced Laser Diagnostics Laboratory
Peak Detector Circuit
Tilt Alarm Circuit