💬 Battery powered glass touch switch

[openhardware.io]

https://www.openhardware.io/view/412/Battery-powered-glass-touch-switch

[Nca78]

First board ready for testing

[Nca78]

Getting really frustrated with this one

Hardware works, script with pin change interrupts works, but when I'm putting it behind the glass it can't detect touch
This is really surprising as the original touch IC is a CT8224 which seems to be a TTP224 clones (on Ali some CT8224 are even sold as TTP224) with no caps or resistors to adjust sensitivity, and I use the exact same size of electrodes, with enough clearance from ground plates (more than on original board...).

I tried to put the CSx capacitors to vary sensitivity, I tried to activate the fast mode, but without improvement,so I'm a bit stuck here ... I guess I have to redesign the PCB to use the existing CT8224, increase the size of electrodes, or both.

If anyone has an idea, I'm interested...

[bilbolodz]

If you decide for redesigning PCB please consider adding external flash for OTA. It's very useful feature.

[Nca78]

@bilbolodz said in Battery powered glass touch switch:

If you decide for redesigning PCB please consider adding external flash for OTA. It's very useful feature.

It is when the battery can withstand the load. But there's no way a CR2032 will survive an OTA update

[bilbolodz]

I've NOT played with CR2032 but with CR123 all is working fine. Of course there is HUGE difference between these batteries but maybe it's worth to try? OTA it's used not very common.

[Nca78]

@bilbolodz said in Battery powered glass touch switch:

I've NOT played with CR2032 but with CR123 all is working fine. Of course there is HUGE difference between these batteries but maybe it's worth to try? OTA it's used not very common.

Max continuous discharge current with CR2032 is around 3mA, it's around 20mA for CR123A I think.
With CR2032 you need a reserve capacitor to avoid voltage drops during TX/RX, it's helping for sending a few messages but no more.

[Edit]
Yes CR123A is a completely different thing, as it's not even the same chemistry.
You can even discharge it at 0.5 or 1A without significant capacity loss...
http://lygte-info.dk/review/batteries2012/Panasonic Lithium Industrial CR123A UK.html

[bilbolodz]

OK, that's interesting data. Thanks

[Baoshi Zhu]

I'm doing something similar but using ESP8266. Saw your article and I had to order a TTP224 touch module to test. I found it is ok. I need to remove Cs to increase sensitivity. Now the button activates when my finger is 5mm away from the pad, even without glass.

[Nca78]

@Baoshi-Zhu said in Battery powered glass touch switch:

I'm doing something similar but using ESP8266. Saw your article and I had to order a TTP224 touch module to test. I found it is ok. I need to remove Cs to increase sensitivity. Now the button activates when my finger is 5mm away from the pad, even without glass.

That's interesting, can you show the PCB you are using ? I've done something wrong with mine but I'm not sure why, seeing a PCB that's running fine would surely help me. Best would be board file, but picture would be fine also if you don't want to share your board.

[Baoshi Zhu]

@Nca78 It is common TTP224 module.

Please ignore the bottom pad as I'm testing conductive foam on that.
Top 3 pads works with Cs removed

[Nca78]

Thank you.
What voltage are you using ? Can you try with 3V or at least 3.3 ?
And what is the distance between the electrodes and the glass ? Because on the switch I use there are a few mm, it's the thickness of the conductive foam + plastic reflector that you can see in the description in openhardware.io.
I am not using any Cs capacitor.

[Baoshi Zhu]

@Nca78 Down to 3V is fine. I've tried a 2025 coin cell. From the touch pad up, I have led diffuser (1.6mm), gap (0.8mm), 3mm glass
The chip marking reads TTP224N-BSB

[Nca78]

Thank you again, looks like it should work in theory as I have similar distance than you between electrode and glass, and bigger pads.
I'll try to replace the TTP224 IC on my test board, maybe it's defective/damaged during soldering. I have the same markings than you on the ICs I bought.

[vikasjee]

@Nca78 , Any update?

[Nca78]

@vikasjee said in Battery powered glass touch switch:

@Nca78 , Any update?

Not yet unfortunately, but it won't be long before I can restart seriously on MySensors, kids will go back to school and I will have more free time

[vikasjee]

@Baoshi-Zhu, @Nca78 , What are the red and black wires under the top pad for? Have you soldered them onto the TTP module touch pads or to the led output?

Have you tried using the other side of the of the touch pads on TTP module since on this side the ICs and other components obstruct the clean surface for the glass panel interface? That side too seems to be sensitive enough...

Also, You seem to have scraped the touch pads and tinned them? Any specific gains?

[Nca78]

Hello, I updated the board, I will double check tomorrow and order before the end of the week.
Changes:

• improved the touch pads, using the restrict layers to have a perfectly constant distance between touch pads and ground plane
• increased size of ground planes and added as many vias as possible, I hope it will improve touch sensing with a "heavier" ground

I also turned the radio to the left, not very classy on the PCB but it allows to leave free space with no traces/ground planes on the sides of the antenna, which is better for radio performance.

[jemish]

Hello,
Any one use CY8CMBR3002 IC in Touch Switch??

[Nca78]

@jemish said in Battery powered glass touch switch:

Hello,
Any one use CY8CMBR3002 IC in Touch Switch??

I have ordered some, not sure if I'll use them or not.

[Wesley]

@Nca78 Do you tested this board, if yes, did it work? And which CS capacitors did you use?