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Topic: 74HC595 output voltage (Read 2 times) previous topic - next topic

goPlayYourGuitar

Well now I just put a 1k resistor and an LED in place of the relay coil and I got 2.24 volts between the output pin of the 74hc595 and ground and 1.3 mA between the resistor and the LED.  Shouldn't I be getting 5v out of the shift register?

MarkT

If you weren't using protection diodes across the relay coils you will likely have damaged the 595 already...  You don't mention if you had diodes.
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goPlayYourGuitar

I used an 1n4002 across the relay coil

James C4S

You've already established that you were over driving the pins of the 595.  It is pretty likely you have damaged it.
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goPlayYourGuitar

I just tried two brand new, right out of the package 74hc595's and they did the same thing.  Only 2.24 volts at the output pin across a 1k resistor and an LED to ground.

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