Capacitive Touch button defeat - Page 1
Forum section: electronics / projects

author: Joust
author_rank: Contributor
timestamp: January 22, 2019, 07:19:08 pm
content: I have a very expensive deskphone headset.it has this annoying and virtually useless capacitive touch bar on the earpiece itself.you can slide to change volume or double tap to mute/unmute.i would like to install a tactile switchi have higher res pics if that will help or is necessary.that ribbon cable has 3 pads for sensing. now I am assuming that the boards solder points to the casing as shown in JabraBottom picture provides the ground reference for the capacitive sensor. you can see the two metal prongs i unsoldered and where the metal goes under the plastic in crescent shapes. IF so this is very poor design wrt to the design guides i have read.The ribbon has the three leads that go to those three pads and the rest are to drive the LED.Now.how can i put a tactile switch to make this go. don't care about the volume so if that is no longer working thats ok but i want to be able to do the double tap to mute/unmute. Where would I put the wires? and do i need a cap in series with the switch? if so, ballpark value??I hope this all makes sense.

author: Yansi
author_rank: Super Contributor
timestamp: January 22, 2019, 07:33:01 pm
content: I would call that almost impossible, as TS is usually extremely sensitive to any capacitance change, so HW modification is out of the game. Please correct me if I am wrong.The CTS is typically calibrated and adjusted in sensitivity for each sense circuit individually, so HW mod could make that completely inoperable. (sensor stuck in detecting or not-detecting state).Also, linear slides usually are comprised of multiple shaped electrodes to enable the linear sensing a possibility. Defeating that with just a HW mod would become extremely complicated.//EDIT: Typo

author: Joust
author_rank: Contributor
timestamp: January 22, 2019, 09:31:38 pm
content: thanks for the comment.i don't give up easythis is kinda why i was thinking of adding a cap in series with a switch.the other side of the coin is how to make it work better.that strip hides under a fairly thick plastic cover. i was thinking i could possibly cut it out and touch the strip directly. there is a thin film over the copper so it should work.I do not care what it looks like. i just want it to work well, read reliable....thanks for the comments.keep em coming.

author: Rerouter
author_rank: Super Contributor
timestamp: January 23, 2019, 01:25:11 am
content: Cap sensing isnt hard to modify. Your idea of a switch and a capacitor is the right start. But you actually need 2 capacitors. 1 to match the original idle capacitance (some controllers are hard coded and wont like this changing) and thr switched capacitor for the pressed state.Just be aware both these capacitors may not be to ground. Some of these controllers use a reference plane that they can toggle high or low.

author: Joust
author_rank: Contributor
timestamp: January 23, 2019, 01:38:15 pm
content: Quote from: Rerouter on January 23, 2019, 01:25:11 amThanks Rerouter. my plan was to leave the original strip in there. that would appease the idle capacitance i imagine and add a wire to a switch.problem is i don't know where the other end of the switch should go nor what capacitance i should use.i don't think i could harm the device by using the wrong capacitor though so i'll suck it and see and try a few today

author: Yansi
author_rank: Super Contributor
timestamp: January 23, 2019, 04:26:21 pm
content: Forget adding wires. Even a few cm of wire will get sense by the TS controller.Rerouter explained what has to be done to fool the controller, at minimum. (My opinion is however there are better things to do than wast time fooling with just phones).

author: Joust
author_rank: Contributor
timestamp: January 23, 2019, 06:36:17 pm
content: Quote from: Yansi on January 23, 2019, 04:26:21 pmnot helpful since i MUST use this thing. i blew the budget buying it thinking it was the top of the line and would do me well...their tech support isn't helpful at all suggesting "tricks" to make it work better by how you hold your hand. which don't work BTW.i'll tinker and see what i can do.

author: Yansi
author_rank: Super Contributor
timestamp: January 23, 2019, 06:47:54 pm
content: Okay, I understand that, however I think that defeating (a defective to begin with) TS controller will make probably for more fun than the whole item is worth. But it is of course up to you to judge.Please keep in mind the capacitances must not change, as the TSC is calibrated for them. Also note the TSC is a very very sensitive low capacitance meter, with a very fine resolution. Any lengths of wire may trigger false positives or not work at all.