Capacitive Sensing Ideas

I'm in the planning phases of a new project and looking for some insight. I'm attempting to bring some technology to the old map with pins in it idea. I'm going to back a large 5' by 4' poster with leds to act as the pins. I'd also like to pair it up with some sort of system to detect a touch to the "pins". Because the leds will be beneath the poster paper and a layer of glass I thought could use 1/8 inch copper tape in an insulated grid pattern in between the leds and use the Capacitive Sense library to get the xy coordinates. The leds will be spaced in a 1/4 inch grid around the continents with a couple of main flight paths across the oceans. Does anyone have any thoughts on how i could do this a better way while still being reasonable priced and embracing the maker spirit?

Bump...

I had another thought as well, would it be possible to use the bus lines for the LED's as the capacitive sensors? Would the ATMEGA328 be fast enough to scan through the LEDs while measuring capacitance and still keep my refresh rate tolerable?

I really don't know how to do this but I'll ask a question that might help get the ball rolling.

How many LEDs?

Measuring capacitance it normally done by timing the rise (or fall) time of a signal, I don't know now many such timings could be performed by an ATMEGA328. I don't think it would be a fast process.

I did a touch sensor circuit 20 years ago that was pretty reliable, but it required you to physically touch a conductive pad.

These days there are a lot of capacitive touch chips around, maybe they could be used as you seem not to have physical contact with any circuit.


Rob

I made some capacitive buttons to control an audio amplifier with the MPR121 Capacitive Touch controller, SparkFun Capacitive Touch Sensor Breakout - MPR121 - SEN-09695 - SparkFun Electronics. It worked really well and was pretty easy.

How many leds? Full/Partial Grid? Can you draw something?

So i'm thinking a partial grid if only to save a few bucks but depending on location each row column could have 50 to 60 led in it. I had thought about splitting it into smaller modules if necessary. This is an image of what that might look like

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What exactly do the Capacitive Touch Sensors do, would that allow me to offload all the timing and active\inactive logic. Also I've been playing around with tinfoil and been adding or removing 1M resistors to hone in on the correct sensitivity. Would the chip allow me to handle that or would i still need the resistors?

Thanks for the responses!

That's alot bigger than i expected, still very possible though.
FlexMatrix Keyboard IC Controllers exist than can do 640 key combinations, 8x20 in 4 sets (PortA-D).
These devices are generally usb/serial.
And serial to i2c is not difficult.

So realistically you could have a 50x60 led matrix 3,000 in 4-5 IC's.

Most modern keyboards, are 3 layers of plastic, that serve as a matrice for the ic.
With some clear conductive paints, varnishes or glues & a lot of time you could be making a 3,000 key board.

And there are shifter register breakouts that allow control for large led matrices.

It is late, i will endeavour to add links later.