Logic probe is useful tool to measure, in a check digital circuits. As a meter, which is used to measure power in electrical circuits. Logic probe was used for detection logic “1″ and “0″ or pulse in a digital circuit. It has a handle. At the head of a pin, for measuring different parts of the circuits, or IC pin. At handle has a state of the LED display, as a “1″ or “0″ or pulse. Before use, to connect the two wires to pinch the power supply. To power the internal circuitry. Can be used with TTL and CMOS.
I compiled the logic probe types, You can create it yourself is not hard to follow.
1. Logic Digital Tester by LM324
This is Logic Digital Tester Circuit. It uses the level input about 5V and use the integrated circuit LM324. Be Main Part electronics perform Drive All LED. Then use Current very low about 10mA by have potentiometer be formed fine the value threshold give just right with the level logic digital both of 3 the level that use by LED1(Green) be the level high and LED2(Red) Be the level LOW and The LED3(Yellow) be the level High IMR . The detail is other please see in the circuit please sir.
2. Mini Logic probe with transistor circuit
This is a Logic probe circuit is one,That is suitable for checking the voltage levels in the TTL circuit. It receives from the circuit being tested.Shows how high or low logic level one.
The circuit when the input voltage to the probe Tip is higher than 2.1 volts (state logic “high”).Transistor Q1 will run the light emitting diodes (LED) LED1 receive direct bias will come out shining. Show the logic “high”(high). When the collector voltage of Q1 running it will fall.and Since the input entered at the end of probe is connected to one end of resistors R4, joint base / emitter of transistor Q2. and Light emitting diode LED2 will get back to bias Q2 and LED2 does not work.
If the input voltage to the late Four home changed to 0 volts (low-level Logistics c), then Q1 is not the current bias is not working.