On 2006-07-15, Farce Milverk wrote:
Hi,

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.

nope indicating an inbetween voltage.

best way is to put the led and resistor in parallel with the pull-up
resistor

+--|---[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 the
other way.



--

Bye.
Jasen