LOGIC_PROBE_1

Published:2009/7/17 1:48:00 Author:Jessie | From:SeekIC

The circuit uses a 4N35 optocoupler (IC1) and a C9013G transistor (Q1). A positive pulse at the base of Q1 turns on the transistor. The 10,000-Ω resistor (R2) limits the incoming pulse so as not to feed too much current to the base of Q1, preventing the transistor from being damaged. With the base of Q1 at a positive potential, electron current flows from the emitter to the collector junction. The incoming pulse also pulls pin 6 high, lighting up LED1 by allowing current to flow between pins 4 and 5. The 330-Ω resistor (R3) provides current limiting for pin 6, although R4 is the current limiter for pin 4. While testing a digital circuit, if the LED lights, that portion of the circuit is in a high state; if the LED remains off, a low is present. The circuit can be placed inside a small enclosure if its connections are made as short as possible.



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