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Experiment 7 - The DISCHARGE Output

From the internal circuit diagram of the NE555 you can see that the DISCHARGE output, Pin 7, is connected to the collector of a transistor. The base of the transistor is connected to the output of the RS latch.


Internal circuit diagram DISCHARGE output NE555.

The transistor is always switched through when the OUT output is LOW.

Circuit diagram measurement of resistance DISCHARGE output of the NE555.

That you can now easily measure with an ohmmeter...

  • If OUT = LOW, the transistor switches through and the resistance drops to near zero.
  • If OUT = HIGH, the transistor blocks and the resistance goes to a very high value.

Circuit resistance measurement of DISCHARGE output of NE555. (Enlarge)

But what do you use the DISCHARGE output for. In the next experiment, it becomes clear to you...