Logic probe yields three discrete states

Posted on Mar 20, 2013

The circuit uses a dual LED. When power is applied to the probe throughthe power leads, and the input is touched to a low level or ground, Ql is cut off. This will cause Q2 to conduct since the base is positive with respect to the emitter. With Ql cut off and Q2 conducting, the green diode of the dual LED will be forward biased, yielding a green output. Touching the probe tip to a high level will cause Ql and Q2 to complement, and the red diode will be forward biased, yielding a red output from the LED

Logic probe yields three discrete states
Click here to download the full size of the above Circuit.

An alternating signal will cause alternating conduction of the red and green diodes and will yield an indication approximately amber. In this manner, both static and dynamic signals can be traced with the logic probe.

Leave Comment

characters left:

New Circuits



Popular Circuits

PWM Motor Speed Controller
BC337 Light Relay Switch By BC547 &
Electronic projects related to computers
microcontroller Seemingly unstable basic PIC18F2550 circuit
hacking rfid for fun
mosfet prevents battery damage
Automatic UPS system wiring circuit diagram (New Design Very simple) for Home or Office
Basic current to voltage converter
Sawtooth voltage controlled oscillator
Level led level meter display driver IC a circuit diagram