inputpcbpcb-design
Is it possible to use a PCB pad as a button? I think of using it to switch on a curcuit that is only supposed to be enabled, when the user holds it in its hands.
As inspiration, I used the pads that are being used on soft touch buttons on keyboards or in calculators:
I know that the human body has a quite high resistance, so what would be an appropriate circuit to detect the touch input? Bare hardware only. I don't want to use any microcontroller here.
Is there a web site that can be fed with the circuit and it would route it and would give me the final bitmap of the PCB?
Querying Google for "PCB Design Service" yields lots of offers, but obviously, you don't just feed them with the circuit but also with (probably a lot of) money. PCB design cannot be fully automated and will be done by humans.
I'll be also glad if you guys point me out to some free software for such PCB routing.
I can recommend KiCad. This software can also work together with online autorouters (which is what you might be looking for) such as http://www.freerouting.net/, but beware that this no "circuit in, PCB out" magic machine. Unless you have a really high number of signals, the effort usesd in correctly configuring the autorouter to produce an acceptable result is much higher than routing by hand. Also you still have to place the parts, which is sometimes the hardest part.
It's a pushbutton switch right-angle, through hole. You probably want alternating on/off action for an on/off switch unless it's a soft switch that just signals a micro or whatever to do the on/off function.
For example, this type:
A parametric search at any distributor should show you lots of options. You may or may not have to order the operator separately.
Best Answer
For reliability reasons I wouldn't go for an open-gate design and rely on the 50Hz noise. It probably might work, but your idea of using interleaved fingers should work quite well.
The resistance of dry skin is somewhere between 1k and 100k, so you could think of an NMOS transistor (find one with ESD protection) and a large pull down of e.g. 1M ohm. Then you can use the finger as a pull-up resistor to turn on the mosfet.
simulate this circuit – Schematic created using CircuitLab
You could also use a bipolar (or darlington) transistor, they are less vulnerable to ESD defects, but cannot supply a large current at the output if needed so you would need to buffer the output.
A capacitive sensor would be an alternative solution, but requires a more complicated circuit.