[SOLVED] Darlington Pair touch input possible??

Hi All,

May be a silly question, but I was wondering if anyone has used a darlington pair as a touch switch for arduino in replace of a momentary switch.

Just wondered if the circuit I found (attached) could be adapted to work obviously with 5v from the arduino. Had a few attempts but can’t figure out how to connect it up and use it in place, pretty much like here http://www.arduino.cc/en/Tutorial/Pushbutton.

Any ideas??



Your schematic is valid, however the electrical resistance of a finger is around a megaohm. I'd suggest reducing/removing that 100K resistor and keeping your contacts as close as possible.

Hi Chagrin,

Thanks for the reply however I’m still unsure how to tap in to this to use it as a button for a digital input. Do you have any suggestions / schematics?

Thanks again.

In your diagram one half of the "0V" side would connect to your digital input pin and the other half to ground (so the pin isn't "floating") through a ~100K resistor. The "9V" side would come from a 5V source on your Arduino.

To light the LED as in the diagram you're aiming for 20ma (.02A) of current. Reducing the 9V in the diagram down to 5V would mean you would need to change the resistor to (5V / .02) = ~250ohm resistor.

Hey again chagrin,

Thanks for the info gonna try and omit the led all together just need the switch part

I'll go away and have a play thanks

Hey Chagrin,

Thanks for the help, thought this wasn’t working at first but it turns out one of my transistors was a dudd!!!
Swapped it out and all working perfectly.

I’ve attached little schematic if anybody is interested and the code used is here http://arduino.cc/it/Tutorial/Button.

Thanks again.

Edit: Transistors are 2N3904’s!!! Sorry.