Joystick Input
A bidirectional analogue reference interface whose middle position is taken as zero; with the lever centred, typically half the supply voltage is read (2.5 V in a 5 V system), and moving from centre to one side produces a command in one direction and to the other side in the opposite direction. It lets a single lever give both direction and speed.
A joystick is in fact a potentiometer; the difference is that thanks to a mechanical spring it returns to the centre position when released and the driver interprets the centre value as zero. The driver subtracts the measured voltage from the centre point: a positive difference sets one direction, a negative difference the other, and the magnitude of the difference sets the speed.
- Centre point drift: With temperature and mechanical wear the centre value can drift by a few tens of mV; the driver can compensate for this drift by learning the centre point when it is first powered up.
- Direction interlock: Since the analogue reference is already a single value, it is impossible for both directions to receive a command at the same time; this is a natural safety advantage over separate direction buttons.
- Broken line risk: If the wiper wire breaks the input is left floating and a random value can be read; putting a pull-down resistor on the input brings this condition under control.
In lifting and platform applications a ramp is applied to the joystick signal to improve the operator's feel; an abrupt lever movement is not reflected directly onto the load.
The context in which this term is used: DC Motor Driver Selection Guide