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Mini Logic probe with transistor circuit

2016-05-08 04:33  
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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.

Mini Logic probe with transistor circuit

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