created: 29 Apr 2013 08:48
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There's an introduction on creating a simple capacitive sensor in the Arduino Playground Forum. It appears to be a straightforward example of building a capacitive sensor, and it is, but unnecessary headaches were experienced because of a basic piece of information not taken into consideration.
When building future projects with capacitive sensors we will want instantaneous results whenever we touch the sensor. Though properly hooked up, the one sensor attached was making a reading only once every 2-3 seconds, as opposed to constantly inputting new data at a rapid pace. Different resistor values, manipulation of the code, attachment of a second sensor, numerous different pieces of hardware, and shouting at the device did not solve the problem.
The code called for three separate sensors to be used, but only one was hooked up to test with, with plans to add the rest once positive results were observed. Therein lay the problem though. Capacitive sensors measure the change in capacitance from an external influence (such as one's finger). The delay in measurements displayed was due to the fact that the code was trying to measure capacitive changes from three sensors, while only one was attached. The delay was the program searching for a capacitive change, which it could not find.
The video below shows what happens when one of the three sensors is unplugged from a properly working device. It is clear that the program does not display new values quickly when a sensor is removed, since the program is searching in vain to find a change in capacitance:
With all three sensors properly hooked up, we can now have instant gratification while using capacitive sensors: