LED coaster

Nice... You could add a touchscreen to the top of the thing to give it responsive feedback. You can get replacement touch screens for phones through eBay for a few quid.

I read a paper somewhere describing the use of the photodiode behaviour of LEDs to build a touch sensor. The idea was to

- turn the LED on and then off

- monitor the voltage across the LED as the parasitic capacitance discharges through the photodiode

If there is a finger over the LED, the voltage will drop off more slowly. I'll try and dig it out. I'd need to redesign the board layout, but providing the timescale on which discharging takes place is short enough, it might well be workable, and certainly would make for a nice effect.

Eben

snip

was this it?

martin

Yes, I believe so. Thanks for tracking that down. As I said, it would be fiddly to integrate exactly their technique with the current scanning circuitry. It should be possible with a clean-slate design, which I probably need to do anyway.

Fortunately my wife really likes her coaster, so I can get away with another 100 quid of PCB fabrication.

Eben

Tam

I have checked ebay for LEDs like the surface mount ones on your coaster.

None to be found.

Please post a link to those you seem to be using.

thank you

donald