Hello everyone,if all goes well i will be designing a touch panel PCB. My question is will it work?
I havent seen it done much/before but the idea is to tie ground and gpio reading pin with a resistor through F. Copper and then have 5vcc on the other side with a small gap for the finger to connect the circuit. Then i will burrow the ground from F. Copper to B. Copper and the exposed circular design will be cut off and masked.
Is there any issues with what im planning or anytips you can recommend beforehand?
This is probably the wrong forum here, itâs more for the kicad software than how to design electronic circuits on general.
The way youâre asking the question, youâre probably a beginner. There doesnât seem to be a direct problem with your design, other than depending on the gpio pin sensitivity you might need an additional transistor as an amplifier. But your question doesnât make much sense otherwise. It doesnât matter if you connect ground through the front or the back layer, at least not for such a low frequency circuit.
I recommend just building it on a breadboard and messing around with it.
On the kicad side, youâll probably want to create your own footprint for the touch button, so reada tutorial on that. I believe there are also some existing touch button footprints in the default library which you could use as a starting point.
Finger resistivity varies in huge range depending on skin humidity at the moment of touching. Capacitance added to circuit by placing finger nearby (even not touching) varies much less (see AT42QT2120 as example).
Have in mind that (depending on clothes, flor, carpet,âŚ) you can have up to 25kV at finger (women up to 30kV). I donât think gpio will like it.
Read about EMC (electromagnetic compatibility), ESD (electrostatic discharge) and HBM (human body model). You even not notice discharges up to 3kV, so if you feel the kick the voltage was higher than 3kV.
You normally donât touch the copper / expose the copper. You should have at least solder mask over the copper and you can have 1-2 mm of plastic.
For normal projects i would use something like AT42QT1070 and do what they say in their documents. For large volume projects you can use a GPIO with AD-Converter of a microcontroller, but it is harder / needs more development.
You are right i was planning to expose copper and use it with a gap and the finger like a bridge,will it need a ADC if i expose the ground and reading wire on one side and positive on the other with a gap between the two that my finger touches to close circuit? (Like a button but the clicky button is the finger)
I donât recommend doing that. The voltage difference between your system and the human can destroy your components. Is there a reason you donât want to use a capacitance sensor, like an AT42QT⌠?
In my opinion you donât need ADC. But you certainly have to protect your gpio against ESD - so between the copper touched by finger and gpio you have to have at least big resistor (like 100k or more) and a capacitor. The better would be to also limit the voltage with diodes and the next resistor after these limiting diodes.
Because of the problems with the exposed copper pads as a button, i donât think this is a simple fast solution.
Something like AT42QT⌠is probably easier and faster.
I mentioned the ADC because you can create a capacitance touch sensor with it, but that is a bit more tricky to implement.
Long ago, it was a dark and stormy nightâŚand my own Touch Buttons.
Different wayâs, depending on the project. Some are now more than 20yrs old and still working.
Often, I simply use Copper Tape for a Contact Switch and/or for Capacitance Touch.
Sometimes I simply use Two Pieces of Copper Tape (or Alum Foil) separated by thin cardboard with Hole (for the pressed Top piece to contact the bottom piece.
Sometimes I simply use Copper Tape for Capacitance Touch with a piece of Acrylic covering it.
Never had a problem with Corrosion (Why? Do some homework to understand âwhyâ and learn the term âSacrificial Corrosionâ and itâs impact). Iâll save you the dissertation and get to the point: Consider making some simple Prototypes of a Touch ButtonâŚ
You can make it real simple with just LEDâs or just a DMM⌠Image below shows an Arduino with some Buttons. Other image shows the guts of a Contact-Switch.
With a couple of Prototypes (and lessons/knowledge learned) youâll be in a good position to assess what you really need for your specific project. If I was interested in making a Clothing item with Button, well, Iâd make a prototypeâŚ
You can buy Conductive Copper Tape at Amazon⌠Look for those with a Conductive CoatingâŚ
Out of everyone who answered you and i are on the most similar wave length,what you are saying is along the lines of what i had in mind,i found 99 percent alchohol dies wonders for cleaning copper so im not worried to much.
But i think i have a good plan here from everyones collective input
I think there is a difference between your finger presses 2 copper plates on each other so they make contact and you use your finger to make contact between 2 copper plates that donât touch each other. The first one is a normal switch/button.
In 1977 (I know the exact year as it was during compulsory work placement before starting studies) I have home manufactured 4 calculators. To make a keyboard I used metal membranes like this one:
The ones I used were round and with 3 points on the perimeter.
Those time I was doing PCBs by painting on them with pen refill after removing the ball from it and then I digested in iron trichloride. Of course PCB was not gold-plated. After year or two my calculators have started to have problems contacting the keysâŚ
