ADC reference voltage settings

The MicroStar Encoder hardware revision 4.0 and later provides hardware jumper options for joystick and trim pot voltages as well as the voltages for the two auxiliary channels. These supply voltages can be either the battery supply or regulated 5 volts. The purpose of this article is to explain a bit about when to use these jumpers and other factors you need to consider.

The joysticks use potentiometers (pots) to sense the joystick position. This is done by applying a DC voltage across the pot and using the voltage on the pot’s wiper to indicate position. The reliability and precision of modern pots is really very good and this is a good method of determine the joystick position.

The Encoder uses an analog to digital converter to read the wiper position and convert it into a digital value used to determine the servo position.

The joysticks typically have a range of about 60 degrees while the pots range is close to 300 degrees. This number varies a bit but for this discussion we will assume 300 degrees. So, only about 20 percent of the pot’s range is used. This means if we apply 10 volts across the pot we will see the wiper change by only 2 volts across the full joystick range. The actual center voltage can be set by setting the pot’s center position with the joystick at center.

The jumpers allow you to use the battery voltage or the 5 volt regulated supply to place across the pots.