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Momentary Hi / Low switch Held High with resistor - How to add LED?


Farce Milverk

Jan 1, 1970

I'd like to add an LED to the following circuit situation:

I have an input line that I hold high using a resistor tied to High.
The other side of the resistor is tied to one side of the momentary switch.
The other side of the momentary switch is tied to GND.

Toggling the switch shows LOW when pressed and HIGH when not pressed on a
Logic probe.
So far, so good.

If I add an LED to the switch (in parallel) it shows high (lit) and when the
button is pressed it goes off, but I lose the LOW signal on the logic probe,
indicating an OPEN condition.

Then I tried placing the LED from the HIGH / Resistor contact point, to GND.
Same problem.

How do I add an LED to a Momentary switch, tied HIGH (or low) via a
resistor, and maintain both HIGH and LOW signals without creating an OPEN




Jan 1, 1970
I may be able to help. I did well in the digital class. But I am having
trouble understanding. Could you post a schematic? Well, a text-based


Jan 1, 1970
What's trollness? Or bottom posting? It posts below the message I am
responding to (Outlook Express).

Farce Milverk

Jan 1, 1970
best way is to put the led and resistor in parallel with the pull-up

+-->|---[330]---+ T
| | ~~~
+5 +---[10k]-------+-+--o o------+ ground
+------ out

led goes on, out goes low, when button pressed

if you want the led to go out use a NC switch and turn the circuit round
other way.

I will try this once more tomorrow - I could not get this to work, same