[Solved] How can I replace a touch switch with one lead with a toggle switch? - Page 1
Forum section: electronics / beginners

author: David4321
author_rank: Newbie
timestamp: March 22, 2023, 08:27:30 am
content: I have a light mounted underneath my desk to illuminate equipment there. It has a touch-sensitive switch which is always turning on when I brush it with my knee, which is very annoying. I opened it up, hoping to disconnect the switch, and connect a simple toggle switch to the leads, and mount that on the side of the housing. But I discovered that the touch switch has only one lead going to it. Can I actually still do the operation I planned, and if so, how to wire it? Below see photos. Many thanks for input.

author: Gyro
author_rank: Super Contributor
timestamp: March 22, 2023, 09:16:04 am
content: Welcome to the forum.I would ignore the touch switch wire completely and put the toggle switch in series with one of the battery leads instead. Hopefully the light will come on when power is first applied anyway, and switching the battery supply will remove the background current drain of the touch switch circuit (microcontroller).

author: David4321
author_rank: Newbie
timestamp: March 22, 2023, 09:25:37 am
content: Thanks Chris,I have to admit I am novice with this. I understand putting the toggle in one battery lead, but I'm not sure what you mean by putting itin serieswith the batteryleadsplural.And also, wouldn't the touch switch still be active when the light is on if I don't disconnect it? I could still end up turning the light off inadvertently by brushing it when it is on. Would it mess it up to just clip that lead? I'd rather just disconnect that switch altogether, if possible.

author: Gyro
author_rank: Super Contributor
timestamp: March 22, 2023, 11:44:13 am
content: Yes, (I did say "one of the battery leads"), just cut one battery lead and insert the switch.With regard to the touch switch, It really depends whether the light will default to 'on' when the battery switch is turned on. If it defaults to 'off' then if you disable the touch switch, you won't have any way to get it to turn on. You might be able to test this by removing and then inserting one battery but your fingers will probably be close to the capacitive touch pad so it is likely to be inconclusive.Even if you leave the touch switch operational, the worst case scenario is that you accidentally turn off the light with the touch switch and forget the toggle switch. That really doesn't sound like the end of the world as you will notice and turn off the toggle switch next time you accidentally turn it on.The board image is a bit fuzzy, but it looks as if the touch pad wire goes via a resistor to the microcontroller input pin. You might get away withshorting this to the PCB ground areadisconnecting the touch pad wire, but equally, it may just fail to turn on with the battery switch then (short answer: I can't tell). The only way to make the light fully 'dumb' would be to remove the PCB entirely and use a series resistor (of some value) for LED current limiting, but it looks as if the microcontroller is probably controlling the LED current using PWM, which is much more efficient in terms of battery life and wasted energy.Personally I would just put the switch in the battery lead an leave it at that, anything else will require experimentation.

author: David4321
author_rank: Newbie
timestamp: March 22, 2023, 12:19:01 pm
content: Thanks so much again for all that, even if some of it is over my head.I am easily able to remove and replace one battery without tripping the touch switch, and it defaults to off when battery is replaced, no matter if light is on or off when battery is removed. I suspect that means it is as you feared, and I cannot cut the wire to the switch without adding components. (Why does this remind me of The Hurt Locker?...)I suppose I'll just add the switch on a battery lead (duh, on rereadingone ofthe leads), and electrical tape over the switch to buffer the sensitivity.Oh, maybe I can't - awful thought: does what you said, and what I found, mean that I need to also turn the touch switch on every time I turn the toggle on, and I'm left with the toggle not really being an on/off switch at all, just a cutoff for the power, so I can't trip it on when I want it off - and the touch remains the real on/off switch? I suppose that wouldn't be so bad, at least I won't trip it on when it's off. Who knew it would take extra circuitry just to replace one type of switch with another...

author: BeBuLamar
author_rank: Super Contributor
timestamp: March 22, 2023, 12:53:54 pm
content: If you want to replace the touch switch you would need to find its output.

author: Gyro
author_rank: Super Contributor
timestamp: March 22, 2023, 01:08:26 pm
content: Quote from: BeBuLamar on March 22, 2023, 12:53:54 pmIt's integrated into the same microcontroller that controls the LED current, there isn't a discrete 'touch switch output'.

author: Gyro
author_rank: Super Contributor
timestamp: March 22, 2023, 01:16:40 pm
content: Quote from: David4321 on March 22, 2023, 12:19:01 pmYes, if the light defaults to 'off' when the power is applied, you will have to retain touch functionality and touch it to turn the light on every time you want it to light. Basically the toggle switch becomes an anti-nuisance switch. Unfortunately you bought a touch operated light rather than a dumber one for the wrong location.P.S. I doubt if electrical tape will significantly reduce sensitivity, a smaller touch pad might.

author: David4321
author_rank: Newbie
timestamp: March 22, 2023, 02:27:37 pm
content: Big thanks for everything folks,Yeah, I searched extensively for that light - the form factor is exactly what I wanted, two aimable lights, right size and shape - hard to find. Only the switch is what it is. Btw, a piece of white electrical tape did reduce the sensitivity significantly.Cheers

author: Gyro
author_rank: Super Contributor
timestamp: March 22, 2023, 02:44:12 pm
content: Good / surprising to hear.

author: David4321
author_rank: Newbie
timestamp: March 31, 2023, 07:38:49 pm
content: Urgh, I finally got around to doing this, and it's not working out. I got a latching push-button switch, mounted it in the housing, cut the red lead from the battery compartment in the middle, and connected the red and black leads from the switch to the two ends. (Black to batteries, red to board.) Now what I've got is this: on first press of button, light switches on, but in lowest brightness. (The light has three brightness levels, switched by subsequent presses of the touch-sensitive button.) But after that, pressing the new switch does nothing, no on, no off, no level changes. When on, I can use the touch-sensitive button to turn on or off, but no level changes. If I pull batteries, then replace, first press turns on again, but same result. I don't actually need the two lower settings, I'd be happiest if I just had the new button do on and off of highest brightness - but could accept new switch as power interrupt, and touch-sensitive switch as controller, as discussed.Could I just bypass the board and touch-sensitive switch altogether, and get simple on/off at full brightness by just leaving button black to batteries, button red to both bulbs, and black from bulbs to white from batteries?One thing - the new push-button has four leads, as it's illuminated; one red, one black, and two blue. I assumed that the blue leads were to feed the led, and the black & red for circuit, so thought if I just taped off the blues, and used the black & red, it would work (I don't care about the led illumination). But as it is wired, the illuminated ring is on, so maybe I am mistaken? (I tried to find a simple two lead switch, but couldn't find one of the size and type I want, with pre-soldered leads - I wanted to avoid soldering leads to button myself.)

author: Jwillis
author_rank: Super Contributor
timestamp: March 31, 2023, 08:37:54 pm
content: Quote from: David4321 on March 31, 2023, 07:38:49 pmIt is likely that the output of the 8 pin chip is PWM. The light brightness changes with each touch near the capacitive senser (Copper foil) . I may be wrong put the pinouts seem to match the WTC02SP 2-Channel Capacitive-Sensing Touch Button Chip(http://en.wincomtech.com/Private/ProductFiles/455991f1a8523d92821c.pdf)The other larger 3 pin chip is a regulator. 5 volt? The smaller 3 pin would be a transistor connected to output.If you want just the brightest setting you can bypass the entire board . You will need to know how the LEDS are configured so you can determine if and what value or values of resistors are required in series with LEDS to limit the current enough to prevent LEDS from burning out.

author: David4321
author_rank: Newbie
timestamp: April 01, 2023, 05:29:58 am
content: Thank you for that Jwillis. Your first paragraph is pretty much above my pay grade. But the second, I understand. I just don't know how to determine resistors that may be needed, and how to implement that. I have a good multimeter, and here are close-ups of the board and one of the LED arrays, in case that helps.

author: kjr18
author_rank: Regular Contributor
timestamp: April 01, 2023, 07:59:42 am
content: Simplest way is to connect red wire form battery to switch, (blue wires of this switch are probably contact wires, red and black are illumination wires probably, as you would need to specify positive and negative for backlight) and from switch to two red wires. White battery wire connect via resistor to blue wires. As for resistor value, it depends on some things: how bright you want to light to be, for lower resistor values you should take into consideration power rating, for 10 ohm resistor it would be at least 0,5W for longer uses; how long you want batteries to last etc. You could even use spare usb cable to skip replacing batteries, if it's possible.

author: Jwillis
author_rank: Super Contributor
timestamp: April 01, 2023, 09:43:44 pm
content: Your good to go. Red wire is positive from battery and positive on LED board. White is Negative from battery and Blue is negative on LED board. Each LED chip has its own current limiting resistor . Connect Blue wires to White wire then connect a switch between Red battery wire and Red LED board wires.

author: David4321
author_rank: Newbie
timestamp: April 02, 2023, 04:51:09 am
content: Yes! This worked like a charm. Many thanks!