Hi-hat normally comes in two parts: a variable sensor on a pedal, and a strike cymbal pad.
How to create an inexpensive DIY variable hi-hat controller...
Useful links:
Linear hall-effect sensor.
Output proportional to the magnetic field.
Operating Voltage 4.5-6V.
Output: 1.3mV/G
FSR = Force Sensing Resistor
Components at Conrad (link).
Thread at V-Drums Form (link).