I'm currently messing around with "capacitive sensors" by trying to light an LED using an Arduino.(Project #13 of Arduino Starter Kit). My capacitive sensor that i am using is just made up of an Arduino,3 wires and a resistor.My set-up is simply 2 wires hooked to an Arduino and both ends of a resistor, with the 3rd wire connected to the resistor on one side, and nothing on the other.
When i am using a 1m ohm resistor,i am getting values in the range of 2700 ~ 2800 when i grasp the exposed end of the wire with my fingers.However, when i try switching the resistor to one with lower resistance ( 10,000 ohm), i am only getting values of 60 when i grasp the exposed wire, and i get values of 0 when i use a 220 ohm wire.
Should i not be getting a greater value by using a resistor with less resistance as that would allow more current to flow through? Yet, the inverse is happening where the values outputted from my Arduino decrease as i lower the resistance and increase as i increase the resistance.
Hello john, thank you for taking the time to answer, but i have just another quick question about capacitive sensing. From the link you provided,it states the following:
Use a 1 megohm resistor (or less maybe) for absolute touch to activate.
With a 10 megohm resistor the sensor will start to respond 4-6 inches away.
With a 40 megohm resistor the sensor will start to respond 12-24 inches away (dependent on the foil size).....
However,as you've mentioned that what i'm measuring is the time taken to change state, and i understand that more resistance = more time taken = higher value, how exactly does increasing the resistance make the sensor more sensitive, allowing it to respond without even touching it(i.e inches away)?
Am i not simply increasing the time taken to change state by increasing resistance? How would that make it more sensitive?!?
The time constant for an RC circuit is R * C. If you increase R then the value of C can be lower for the same time constant. Your circuit is therefore sensitive to smaller changes in capacitance.