Hardware Reference
In-Depth Information
Figure 4-11.
With two of the same value resistors between voltage and
ground, the voltage between the two would be half of the total voltage.
Without getting bogged down in the math involved, if you removed the 10K
resistor connected to 5 volts and replaced it with a resistor of a higher value,
the voltage going into the analog pin would decrease. If you removed that 10K
resistor and replaced it with one of a lower value, the voltage going into the
analog pin would increase. We can use this principle with sensors that are
variable resistors in order to read them with the analog input pins. You'll sim-
ply replace one of the resistors with your sensor.
To try the circuit out, you'll wire up a type of variable resistor called a
force
sensitive resistor
, or FSR.
Force Sensitive Resistor
A force sensitive resistor is a variable resistor that changes based on the
amount of pressure placed on its pad. When there's no pressure on the pad,
the circuit is open. When you start placing pressure on it, the resistance
drops.
The exact figures will depend on your particular FSR, but typically you'll see
100K ohms of resistance with light pressure and 1 ohm of resistance with
maximum pressure. If you have a
multimeter
, you can measure the changes
in resistance to see for yourself, or you can look at the component's
data-
sheet
which will tell you what to expect from the sensor.
