What Is a Digital Potentiometer?

How Does It Work?

Inside it there are series-connected resistors and electronic switches. A microcontroller sends a command over I2C or SPI to select the "wiper" position; so the resistance is set digitally.

Difference From a Mechanical Potentiometer

A mechanical pot is turned by hand and wears out; a digipot is set by software, doesn't wear and can be controlled remotely. But it's limited by the number of steps (e.g. 256) and has a low power-handling capacity.

Volatile and Non-Volatile Setting

Some digipots lose the setting when power is cut (volatile); others store the last position in an internal EEPROM and restore it at startup.

Where Is It Used?

Volume control, automatic calibration, programmable gain/offset adjustment, contrast adjustment and test equipment.

Rheostat and Potentiometer Connection

A digipot can be connected two ways: in three-terminal potentiometer mode as a voltage divider (the wiper output is adjusted), or in two-terminal rheostat mode as just an adjustable resistance. For gain adjustment the voltage-divider mode is usually used, and for current/time adjustment the rheostat mode.

Common Mistakes

• Current limit: a digipot doesn't carry high power; it isn't suited to direct power control.
• Step resolution: a low-step pot falls short where fine adjustment is needed.
• Volatility: if a persistent setting is needed, an EEPROM model should be chosen.