Safe, Contact-less Virtual Buttons!

RE: Safe, Contact-less Virtual Buttons!

navadeepganeshu — Sun, 12 Jul 2020 12:40:23 GMT

Excellent project!

>> What exactly is the purpose of LC tank (oscillator) for sensing? Won't just measuring capacitance change work insted of using LC tank and measurig the change?

>> Are you supposed to program the onboard MSP430 to run this sensor or does it come with ready loaded firmware ? Is it customisable?

>> How does MSP430 onboard connect to computer without USB interphase circuit ? (Like we have debugger part for launchpads)

Kindly help me in understanding the following.Thanks.

RE: Safe, Contact-less Virtual Buttons!

thepenguinmaster — Thu, 09 Jul 2020 12:52:33 GMT

Cool project! I am inspired!

RE: Safe, Contact-less Virtual Buttons!

weiwei2 — Thu, 09 Jul 2020 03:18:11 GMT

great project

RE: Safe, Contact-less Virtual Buttons!

yuricts — Wed, 08 Jul 2020 17:03:58 GMT

Hi Shabaz,

Congrats with your prize.

Nice project!

RE: Safe, Contact-less Virtual Buttons!

shabaz — Mon, 15 Jun 2020 19:40:31 GMT

Just as an update, to turn this project into something more usable, I've gone ahead with designing PCBs for it.

I've gone with a dual-PCB option. The first board contains the four touch-less sensor areas and sensor chip and flat flex connector.

The second board is the controller board and it can sandwich behind it at a suitable distance, and contains two flat flex connectors (so that a total of 8 buttons can be attached).

I've gone with STM32WB55 for the microcontroller. It has a lot more power than the chip on the FRDM board that I used for the blog post. It's a 64 MHz Cortex-M4F which could be handy if any more complex filtering is needed in future.

Also, that STM chip has BLE : ) so no need for wiring in some installations, i.e. backhaul the button-presses over BLE to another device. The board will be powered from a rechargeable cell (or can be powered via USB connector).

I'm excited to see it functioning hopefully! I'll report more soon as the design progresses - the first PCB design is complete, and the schematic for the controller board is nearing completion.

RE: Safe, Contact-less Virtual Buttons!

Andrew J — Mon, 18 May 2020 08:42:02 GMT

Fascinating! I wonder if this is the technique used on non-touch toilet flushes.

RE: Safe, Contact-less Virtual Buttons!

Fred27 — Mon, 18 May 2020 08:18:27 GMT

I was about to offer you a spare PCB for my lock which I found lying around - but then I realised it uses mutual capacitance with the buttons arranged as a 3x4 grid, so probably not any use to you. Let me know if you think you could make use of it though.

Likewise, if you wan to borrow an MSP-CAPT-FR2633 kit which has various example button layouts then ping me a message.

RE: Safe, Contact-less Virtual Buttons!

Fred27 — Sun, 17 May 2020 18:42:39 GMT

These buttons may be a little less sensitive to electrical interference compared to the usual charge time sensors, but they will still be affected by stray capacitance. I found that on my lock even the proximity of wiring behind the device made some buttons less sensitive than others.

TI have some good information on PCB design which are aimed at their CapTIvate MCUs but I'm sure will apply to any capacitive sensor. Search for CapTIVate Design Guide in Resource Explorer (within CCS). Or this links directly to it online. This also looks useful: https://training.ti.com/node/1138868?context=588332-1138868

RE: Safe, Contact-less Virtual Buttons!

Fred27 — Sat, 16 May 2020 22:36:21 GMT

I think it's a good idea to keep a bit more free space around those capacitive touch pads. They can pick up noise from other traces. (I'll take a property look tomorrow when I'm not on my phone after a few beers )

RE: Safe, Contact-less Virtual Buttons!

shabaz — Sat, 16 May 2020 22:03:40 GMT

I figured I'd try to squeeze it between the sense pads.. It's still 2-layer, and is now a 48 x 48 mm board.

No idea if it will perform as well, but I think it is worth a try.

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RE: Safe, Contact-less Virtual Buttons!

shabaz — Sat, 16 May 2020 19:37:30 GMT

Here's a first draft of a potential PCB for it.. the idea being that the microcontroller board is separate, so it can control (say) up to four of these, for a total of 16 sensors.

I thought about a hole in each pad, or holes (e.g. small perforations), for a light indicator. Maybe that's not necessary for a first version, and any feedback can be via a display or speaker on the microcontroller board.

All the parts are surface-mount, so the other side is flat, with the pads etched on that flat side, so the board could be taped or glued behind a plastic or glass panel.

In theory, with a 4-layer board, I could perhaps have the circuitry directly on the pads, and reduce the PCB size and make it more versatile. The added capacitance of the inner ground plane should not cause much of an impact since it is a static additional capacitance. But I don't really know for sure since I have not tried it. Since I'm not envisioning being restricted for space, I figured I could just have the circuitry to the side for now, with a 2-layer board.

Any ideas or suggestions are welcome.

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RE: Safe, Contact-less Virtual Buttons!

genebren — Fri, 15 May 2020 21:54:14 GMT

Excellent project design. These contacts (or non-contacts) look like they could work well even while wearing gloves (another good way to avoid contact).

Yet another example of your well designed designs. Extra points in my book for re-using parts from other projects.

Well done!

RE: Safe, Contact-less Virtual Buttons!

ralphjy — Fri, 15 May 2020 20:17:48 GMT

Very cool and I agree with a Frank that it’s a great application of FFT.

The only concern I would have in practical use is that you can’t prevent contact.

RE: Safe, Contact-less Virtual Buttons!

three-phase — Fri, 15 May 2020 19:37:06 GMT

Great idea and well presented.

Kind regards

RE: Safe, Contact-less Virtual Buttons!

fmilburn — Fri, 15 May 2020 19:17:28 GMT

Hi Shabaz

Very cool and looks great. Clever use of FFT. I would not have guessed it could be that selective but I wouldn’t have thought of using FFT to bucket it either.