Digital Potentiometers
Intro
Digital Potentiometers. Ohh boy, where to start… from the basics.
Digital potentiometers are used to adjust volume and brightness and if you pair them with an operational amplifier they become a digital-to-analog converter! So what is a digital potentiometer?
Overall
A digital potentiometer is a type of electronic component that functions like a traditional mechanical potentiometer but instead of a physical wiper that you turn or slide, you send a digital signal to adjust the resistance. This allows us to control it remotely, or automatically, based on the output of other sensors or control systems.
Architecture
As you can see the digipot comes in a very compact size as compared to a mechanical one. Inside we have -Surprise Surprise! An array of resistors connected in series. In each junction of two resistors, we have a CMOS switch and those are connected together at a single point. The terminals are connected to each of the extremes and to the wiper which is the active CMOS switch.
This structure gives the digipot immunity to physical environmental changes such as vibration, shocks, and wiper contamination.
Adjustments
In theory, a mechanical potentiometer has an infinite resolution. But, due to physical factors, you actually get a low precision. Let me show you what I mean. Here I have a power supply, I would like to set it to five volts… Whoops… too much, whoops too low… You see! It is not really as accurate as you think and if I will measure the voltage output with a DMM, I will get a slightly different result. [record a blooper here]
In a digital potentiometer, the wiper position is determined by the RDAC register. This means that you can set the desired value millions of times if not, infinitely! The adjustment can be done in three ways – SPI, I2C, Up/Down, or manually with push buttons.
All of those you can find on our webpage – tme.eu. But not only! You can also select the communication interface, resolution, or memory.
Memory Technology
Yes! Digipos have or don’t have memory. In the case of volatile memory, if the power supply is disconnected the digipot forgets the RDAC position and sets it to the manufacturer's value which is usually in the middle.
Fortunately, vendors added an EEPROM-based non-volatile memory that can save the position of the wiper and restore it even after 100 years! So don’t worry if you quit playing your guitar, your settings are saved. Speaking of which – check those tools from Wera. Witek tells us all about the set and even plays some crazy riffs!
Disadvantages
Since digipots are encapsulated they are less vulnerable to vibration, less accessible to physical tampering, and can offer more features than the traditional potentiometer. But every good story has a but. And here is the butt.
Digipots cannot handle high-power applications, they cost more than traditional ones, they need an external control system and, although they have controllable resistance – the resolution is still limited… I mean – 256 steps. Please tell me you are OK with only 256 colors on your screen… Yea. I thought so
Summary
In short - digipots are used to adjust the resistance in a circuit. They offer programmability and the ability to control resistance remotely but may have limited resolution, power handling capabilities, temperature range, and lifespan compared to traditional potentiometers.
I hope you know more about digital potentiometers now. Stay tuned for future basics episodes :D