Transparent single-surface touch foil - Page 1
Forum section: electronics / projects

author: i_like_sparks
author_rank: Contributor
timestamp: March 29, 2021, 06:12:59 pm
content: Hello,for an LED project I would like to have an RGB-colored backlit diffusor surface with a capacitive touch sensor. The surface is far enough from the PCB that I haven't managed to get it working with buttons/loops printed on the PCB itself, so my best guess would have been to go with a transparent capacitive touch foil that is glued to the surface. I only need to detect touch/no touch, but I cannot seem to find such foil in small quantities and without having it custom made with custom connector etc. The ready-made ones have a full matrix layout and cost >$30, which is too much as I'll need a few dozens.I really only need a moderately transparent material that is conductive and that I can hook up a wire to, even better if it can be cut to size, but I can't seem to find such a thing. Any suggestions?

author: t1d
author_rank: Super Contributor
timestamp: April 01, 2021, 03:46:43 am
content: It is a little hard to envision what you are describing, but, if I understand correctly, you need a clear material for a capacitive switch. I take it that you need to view information that is underneath the switch pad. Might you use two v-e-r-y thin traces, or wires embedded in the switch plate surface? The switching circuitry will need minimal voltage and current to engage the circuit, so there is little concern with applying a bare finger to the wires. The PCB houses are now able to produce microscopic traces that would be hard to see with the naked eye and would not interfere with reading the information.It is typical to find these switches built up on a demo board with two bare copper pads used for the switch plates. They are cheap on Ebay/etc.https://www.amazon.com/s?k=capacitive+switch+module&ref=nb_sb_nossAlso, for the switch that is separated from the PCB by some distance, maybe use a separate amplification/booster circuit behind the switch?I hope that helps, or gives you some ideas.

author: i_like_sparks
author_rank: Contributor
timestamp: April 01, 2021, 10:58:09 am
content: Thanks, maybe to clarify: imagine a plexiglass cube with RGB LEDs in it. Each side should react to being touched but also evenly show the color of the LED from inside, so I can't have any solid plates or larger wires that would cast shadows. The contact size is about 10x10cm.I'm not sure how to understand your idea with the printed traces - did you mean printing them on flex PCBs?I could use wires but the contact size is quite large, so I would probably need a grid, which makes it a bit of a pain to build.I'm basically just looking for a simpler/cheaper version (just a simple button, not a full grid) of the touch foil that every touchscreen/mobile phone uses.

author: dmendesf
author_rank: Frequent Contributor
timestamp: April 01, 2021, 12:28:49 pm
content: I think you need ITO coated plastic:https://www.amazon.com/ITO-Indium-Oxide-Coated-Plastic/dp/B00JFJJ5P8

author: i_like_sparks
author_rank: Contributor
timestamp: April 01, 2021, 01:35:02 pm
content: Thanks for the keyword, that seems to be the right direction. A little expensive though, I need about 1m^2 total. Do you have any experience with this? I'm wondering how to attach wires, as apparently it can't be soldered.

author: dmendesf
author_rank: Frequent Contributor
timestamp: April 01, 2021, 01:39:06 pm
content: No I don't. Just saw somewhere that's how touch screens were made. There's also ITO coated glass. I think I saw someone homemading it on youtube but I don't know how safe it is.