Do you know the functioning of a digital potentiometer, do you know what it is for, what is its importance within electronics? If your answer is no or if you have any doubts about the subject, come with us to learn a little more, in this article we will cover what is a pot without mysteries.
The digital potentiometers appeared with the purpose of replacing the analog mechanical potentiometers, in the most diverse practical applications, for example, to regulate the volume of the loudspeakers of a sound device, these potentiometers are in fact resistive chips, very different from their prime potentiometers analog, they use a digital control to effect the variation of an analog voltage signal within a circuit.
The chips known as digital potentiometers vary the resistance, according to the active digital inputs of the chip, that is, through digital inputs and their bit combinations we can impose a variable resistance value to a circuit, this control can be performed manually or through a microcontroller.
The principle of operation of a digital potentiometer is simple, each pin or digital input of the resistive chip is responsible for a respective set of resistance, when one of the pins of the chip is activated by a digital signal, the resistive block corresponding to the digital input or pin the chip is inserted into the main circuit. In this way we can increase or decrease the resistance of a circuit, through the control of the digital inputs of a chip or digital potentiometer, therefore, through a digital control we exercise an analog voltage variation in a circuit. There are digital potentiometers of different amounts of bits, that is, digital inputs, we usually find digital potentiometers from 4 bits to 8 bits (most common digital potentiometers).
An 8-bit digital potentiometer or 8 digital inputs can offer 256 different resistive combinations in the circuit. resistance inserted in the smaller circuit will be the output signal of the voltage in relation to its initial input.
The analog mechanical potentiometer is a resistance that can be varied according to the need of the circuit, the resistance is varied by moving a metal shaft that has a movable contact at its end.
Note that the figure above shows a mechanical analogue pot with three terminals. When we measure the electrical resistance between terminal 1 and terminal 3, we find the total value of the resistance of the potentiometer, but if we measure the resistance between terminal 2 (central) for any other terminal, we observe that the resistance found will be adjusted, by the central axis that has the cursor (moving contact).
Its operation is due to a strip of coal called the track, where the moving contact of the cursor moves when moving the moving contact it closes the resistance at different points, this moving contact is attached to the rotating axis, thus, the resistance between the central contact depends on the position of the cursor.
Operation and application of potentiometers
The potentiometers in general (both digital and mechanical) can be used in two ways, the first way as a voltage control or analog signal, while the second way the potentiometer can work as a rheostat .
As a voltage regulator we can say that the potentiometer will cause a voltage drop proportional to the position of the cursor or the number of digital inputs activated. To understand the situation illustrated, we call “C” the position of the cursor or the number of active bits in a potentiometer, so “C” is given by a percentage of the cursor rotation in the mechanical potentiometer or the number of active digital inputs in the digital pot. So we can understand, for example, if the stroke is exactly half or the active bits of the digital potentiometer are exactly half, we will have, “C” = 50% so the output voltage will be exactly half of the input regardless of the value of supply voltage of the pot.
The mechanical and digital potentiometers can also work as a rheostat, whenever only two of the potentiometer terminals are used. When it works in this way, all current in the circuit will travel through the potentiometer and it will work as a variable resistance generating a voltage drop before the load, the rheostats are used in industries for motor control, they are specific for very high powers different from the potentiometers described here. Digital potentiometers that work in this way generally use a transistor in parallel so that the largest current in the circuit runs through the transistor and not the potentiometer, for example, the temperature regulators of modern electric showers.