Hello,
I am trying to build the touch switch linked below. I want a touch switch that needs only one touch pad and this seemed ideal.
I just can't get it to work. It is always on.
I was trying to build it with just an npn transistor in place of the darlington. I'm just trying to turn on an LED so don't need a lot of power running through it. I thought that might be my problem so I improvised a darlington with 2 npn transistors. That didn't work either.
HELP!
Any ideas??? Should it work? **broken link removed**
The circuit in the link doesn't have a Darlington??
Edit:
You could try this form of touch switch (which requires points a and b to be bridged by a finger). R2 provides some protection against ESD.
To use components you may already have, use R1 = 2 x 1meg, R3 = 1meg, C1 = 470nF.
The schematic calls for a BD679 as the transistor. The datasheet for a the BD679 says "Monolithic Darlington configuration with
integrated anti parallel collector-emitter diode" That sounds like a Darlington to me!
I don't have two contact points available to me on my project. I want to be able to turn on the LED on an LCD by touching the frame. At least that was my hope.
The circuit in the link doesn't have a Darlington??
Edit:
You could try this form of touch switch (which requires points a and b to be bridged by a finger). R2 provides some protection against ESD. View attachment 81768
To use components you may already have, use R1 = 2 x 1meg, R3 = 1meg, C1 = 470nF.
That's a pity. Skin resistance is a major factor with that contact-bridging type. Also, did you have the inputs of the 2 'spare' gates in the 4011 package grounded? CMOS circuits with floating inputs can misbehave.
Sorry. That was poorly worded on my part. I understood what you meant the first time. Thanks again.
Before I try the one I posted again, does it even look to you like it should work. No use in trying again if it's complete junk.