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What is PWM and how can it be read?
The term PWM is an abbreviation of “Pulse Width Modulation”. It is nothing else than a method of controlling electronic circuits with the help of manipulation of the control signal itself, or more specifically, its technical parameters. This results from the physical characteristics of the PWM signal itself, which consists of the previously mentioned pulses. Their basic parameters concern the time and width of the PWM pulse. What does this mean exactly?
The width is the ratio of the time during which an electrical charge was delivered to the connected receiver during one PWM pulse. For example, if the measurement of the PWM signal shows a frequency of 300 Hz, then the time of each full pulse will be 1/300 of a second [3,(3) milliseconds]. Similarly, we can calculate the time during which the current will be delivered during one PWM pulse – we only need to multiply the previously obtained result by the filling.
So how is the PWM signal measured? The easiest way is to measure it with a laboratory oscilloscope. Then you also get its direct graphical interpretation.
The current will flow through the circuit in steps, and the width of each pulse will be determined by the fill factor illustrating the time during which power was applied to the receiver. The wider the individual “hills” are, the longer the power will be applied.
On the other hand, if the measurement of the PWM signal on a laboratory oscilloscope shows a continuous line (assuming a value greater than 0), this means that current is flowing continuously to the connected receiver, and thus the fill factor will be 100%.
Where does PWM find its application?
PWM signal is used, among others, in impulse power supplies, which thanks to it are able to control devices connected to it. Most often, however, this type of signal is responsible for the precise regulation of the rotational speed of an electric motor, although it can also act as a lighting controller.
PWM pulse is equally often used in fans. It allows to adjust the efficiency of the flow of air pumped through them, while minimising the noise generated by individual fan blades.
PWM can also be found in pulse amplifiers, as well as control systems whose primary task is to manage the operation of servomotors. This is why precise measurement of the PWM signal is so important in projects based on microcomputers from the Arduino and Raspberry Pi families.
How to use PWM signal modulation?
You already know where the PWM signal is used. But what does this mean in practice? All kinds of current consumers such as electric motors, light bulbs, LEDs and also servo motors, among others, have to do with it. All such devices can be controlled using the pulse width modulation phenomenon.
This is why the PWM signal is at the heart of many projects based on development boards from the Arduino family. With this kind of minicomputers it is possible not only to measure the PWM signal, but also to generate it practically in any way. Using the “pwmCounter” and “pwmValue” functions, it’s enough to write a relatively simple code to manage external modules and devices connected to the Arduino minicomputer. In the simplest terms, a specific output pin of the board will alternately switch on and off in a strictly defined, small time interval.
So how to use the PWM signal in practice? With this signal you can easily adjust the brightness of the LED used for example to illuminate the environment in the frame of the camera connected to the microcomputer. In this case, however, you should remember that the frequency of the generated PWM signal should coincide with the aperture parameter of the camera – otherwise the image will be exposed to the formation of characteristic artefacts deteriorating the quality of recorded video.
