Logic Probe circuit show in figure 1 consist Op-amp LM358. It indicates the logic state of the node of any TTL logic circuit.
Figure1 Schematic of Logic Probe
indicatees feature :
If The level is Low, the probe will display a "zero" (0) and only the red LED will be lighted. If the level is High, the probe will display a "one" (1) and only the green LED will be lighted. If the level is Impedance, the probe will display a nothing and no LED will be lighted. The logic level is "Low" when the "Test" wire is connected to the ground of the circuit (the voltage is between 0V and 2V). The logic level is "Impedance" when the "Test" wire is unconnected (it has no voltage or the voltage is between 2V and 3V). The logic level is "High" when the "Test" wire is connected to the positive supply of the circuit (the voltage is between 3V and 5V).
Logic Probe
