Logic Probe for Tri-state Logics

This is a simple circuit of Logic Probe for Tri-state Logics. This circuit can be built only in a few hours. Besides that, this circuit has some other advantages such as it is cheap, has high performance, and the LED will only light when tip of probe is touching a voltage source. A plastic ball-point pen can be used as chassis, so the logic probe has style and personalized touch. here is the circuit :

It’s very easy to use this logic probe. Just connect the power (alligator) clip to the circuit’s power supply and then touch the probe tip to the point that will be tested. If the voltage is less than 9/20 the power supply voltage, the LED will light green. The LED will light red when the voltage is greater than 11/20 the power supply voltage. The LED will appear orange because the LED oscillates between green and red due to A high-frequency signal. [Source: Swanson Technologies]