What Is a Digital Potentiometer?
A digital potentiometer is an integrated circuit that digitally controls the sliding element (wiper) of a variable resistor, simulating the function of an analog potentiometer.
Unlike analog variable resistors, digital potentiometers do not have mechanically-moving sliding parts, making them structurally robust, resistant to failure, and highly reliable for long-term use. When combined with a microcontroller or other device and mounted in an analog circuit, the amperage can be automatically adjusted while freely controlling the resistance value.
Uses of Digital Potentiometers
Digital potentiometers are used in audio equipment and digitized home appliances, such as AI speakers and LED dimmers. Since they can be described as digitized variable resistors, they are used as an alternative to analog circuits with sliding parts.
For example, they can be used to digitally control the volume adjustment of audio equipment or the brightness and contrast adjustment of displays, which used to be controlled by physical dials. As smart home appliance technology has progressed in recent years, there is a growing demand for digital control of analog values, driven in part by compatibility with AI speakers.
Principle of Digital Potentiometers
The principle function of digital potentiometers lies in the operation of a variable resistor. The resistor’s sliding wiper, once mechanically-operated, is now controlled by a Once mechanically-operated by a sliding wiper is now switched and controlled by a combination of a digital circuit and a resistance.
The analog circuit consists of a series of fixed resistors, and the connection points are switched by COMS transistors. This allows the variable resistor to switch resistance values in response to signals from the digital circuit part.
The digital circuit consists of an up-down counter, a nonvolatile memory such as EFPROM, and a decoder. When the desired resistance value is input, it is written to the counter and written to the nonvolatile memory.
This information is read out by the decoder, and the CMOS transistor corresponding to that value is switched on. The value of the variable resistor can be set quasi-statically by digital input. External inputs are stored in nonvolatile memory, so the information is preserved even after the circuit is turned off.
Other Information on Digital Potentiometers
1. Replacement of Analog Adjustment Trimmers
Nowadays, as typified by digital home appliances and IoT electronic devices, analog mechanical adjustment is being replaced by programming-based digital control. In the case of analog adjustment, the final step in the production line is manual adjustment before shipment, but by using digital potentiometers, automatic adjustment is possible through microcomputer control and other means.
Automatic calibration is also possible, increasing equipment precision. Unlike mechanical analog adjustment trimmers, adjustment by outside parties unfamiliar with the digital control code is impossible, providing significant security benefits.
Because of this high level of reliability, digital potentiometers have recently been widely used in entertainment equipment, where volume and LED contrast are important.
2. Digital Potentiometer Digital Control Method
The control interfaces for digital potentiometers usually include the Serial Peripheral Interface (SPI) interface, I2C interface, and UP/DOWN interface. Furthermore, in applications where a digital potentiometer requires continuous variation similar to a D/A converter, attention should also be paid to the clock frequency during digital control.
The maximum frequency is typically about 3 MHz, but it is important to check the product specifications in advance. Application software for these controls is usually available from the manufacturer, and technical support is also provided if necessary.
In some cases, a development support kit including a Graphical User Interface (GUI) is also available for users who wish to develop their own programming software.