Hello,
I want to digitize some sensors and a touch panel with a FPGA. FPGA allow a certain flexibility but good external analog parts are necessary.
In my context, the trouble comes from the screen's touch panel (classic low-value resistor type with 4 wires). I know that it is very sensitive to the environment (temperature, power supply, interferences...) and drift is very annoying (1% is maximum allowable) so precision parts are required (a good analog comparator instead of just a digital CMOS input, low-drift capacitors etc.).
My current idea is to create a VFO where only the touch panel resistance influences the frequency. The FPGA counts the number of edges during 1/50s (given by a Xtal) and this gives a ratio of the resistance, software then scales the results.
But I also want to make it consume as little current as possible. This seems difficult to reconcile because the higher the frequency, the better the converter resolution, but also the more edges and power consumption.
Does anybody know a better method that is simple, economic, power-efficient, reliable and stable ? What type of circuit is commonly used ?
thanks for any insight, yg