Digital Potentiometer

Digital Potentiomter – Working, Internal Structure & Applications One of the most common types of variable resistors is the potentiometer. Potentiometer or “pots”, are three terminal devices, used to vary the resistance in a circuit. We have dealt in depth about this topic, in our article “potentiometers”, if you want to learn about the basics of a pot, this article will be useful for you. Pots that ware available nowadays varies in operation. Some are mechanically operated, while some are digitally controlled.   Image Credit – SparkFun Before we proceed, let’s have a quick review of how the basic working of a potentiometer. How Digital POT Works? Generally, a pot has a resistive material over which a wiper moves. This movable wiper controls the resistance offered by the potentiometer. A pot as we know has three terminals, a positive, ground and a wiper terminal. The position of the wiper decides the resistance of the pot. To understand its significance, lets consider the figure below.   Look at the above figure. What do you see, a simple resistor right? Well, there’s more to that. The numbers 1, 2, 3 here indicate the terminal numbers. Terminal 2, indicates the wiper terminal. Now the resistive part between terminals 2 and 3 is nothing but the effective resistance of the pot. So according to this, the effective resistance of the pot, for the first case, where the wiper terminal is nearer to the terminal 1,is higher than that for the second case( wiper terminal nearer to terminal 3). Now, how to change the position of the wiper? you may wonder. The wiper movement can be controlled either mechanically or digitally. This difference in control of the wiper, brings us to the classification of pots into mechanical and digital potentiometer. The figure below shows a schematic of a mechanical and a digital potentiometer.   First, let’s see what is common to both of them: Basic structure: Both have three terminals and a resistive element, over which the moving terminal glides. Adjustable Nature: The resistance of both types of pots can be adjusted to the need of the circuit, and offer wide range of resistances. Now, if they are similar in structure and nature what’s the difference between the two? Well, the biggest difference between the two is in their control section. Control section is nothing but the part of the pot that controls the position of the wiper. In mechanical potentiometer, the wiper movement is done by hands or we can say physically. In digital potentiometer, the wiper connection is electrical and the movement of the wiper is controlled by digitally controlled signals, typically given out by a computer or a microcontroller. The types and working of a mechanical potentiometer has been already discussed in our articles “potentiometers”. Here in this article, we will deal with the working of digital potentiometers and their advantages over mechanical pots. What is a Digitally Controlled Potentiometer? A digital potentiometer or a digiPOT (Electronic Potentiometer) as it is commonly called can be said to be a digital version of the mechanical potentiometer or a rheostat. It offers the same analogue functions as a rheostat or a potentiometer that is control of current or voltage. It is controlled by digital protocols like I2C , SPI, and basic up down and push button protocols. This device allows a more accurate robust and faster calibration process, with smaller voltage glitches. How is digiPot different from the traditional Pot? The Build: Mostly, the digipot is built from a resistor ladder integrated circuit. Here, at each step, there is a switch that connects it...
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