AVR Capacitive Touch Sensor Slider and Spinner

This is a demonstration of a firmware-based AVR slider and spinner using capacitive touch sensing. It uses two zones to create a slider object and three to create the pinwheel object.

This is an ATTiny44 (not 24 like I said) running at 5v, and 8 MHz. It's communicating through the USBTinyISP via a tinyispterm program I wrote.

Category:

Science & Technology

Tags:

• AVR
• ATTiny
• tinyisp
• touch
• capacitive
• sensor
• slider
• spinner
• wheel

[MrBarcode]

Could we possibly get a high res photo of the wheel and slider?

[CNLohr]

@MrBarcode PCB-design-wise, or something else? I don't know where this this thing went... But I do have other slider for my glass PCB thing.

[artem1kuchin]

Ah! Also,  looking at the circular sensor i don't see the ground connection. I see the three measured channel, but not ground (relative to which the capacitance is measured). Is it on the back of the pcb or is it absent and you measure the capacitance relative to floating remote ground?

[CNLohr]

@artem1kuchin Your body provides a sympathetic? (probably wrong word, maybe intrinsic) ground. It doesn't matter if it's /actually/ attached to real ground since you can hold a lot of charge, and it's all relative voltages.

[artem1kuchin]

What method do you use to determine the finger press? As far as i see you have only the Rs for each channel. Do you just measure the time to charge and discharge the capacitance between selected channel and ground? At what rate? What value of R do you use?

[CNLohr]

@artem1kuchin I use a 1 M-ohm Rs for each channel. I measure the time charge, specifically. I set the pin low, and enable output, then I start the timer and disable the port drive, let the line drift high and bingo.

[artem1kuchin]

@artem1kuchin one more thing, AFAIK human body for cap sensing is considered a conductore, not the charge storage, so, the body connects your terminal with so called remote ground (through the air and other materials).

[artem1kuchin]

@CNLohr how much time does it take to make one meaxurement?

[artem1kuchin]

@CNLohr I see. I used this method and failed measurably when the whole thing was turned on in an environment with EL light with electronic ballast and no real ground around. The EL light generated enogh EM noise to make things go crazy. So, this is why noe devices use charge transfer method, so, capacitance is measured to some really known and stable level, like common wire.

[123bndresch]

Thanks for the reply. I found the CapSense library for Arduino, so I will try to test it out tomorrow. I was looking at the cap sense slider on the STM32F-Discovery schematic and they use 4 chevron sensor footprints in a row... I guess so that they can extend the length of the slider. Very cool technology indeed... just etch that human interface right into your circuit board.