# Pwm signal

What are the applications of PWM? The Prototyping Board Setup. This feature provides microcontrollers by a mean of, seeminglyoutputting analog values of voltage between v. Instead of outputting digital values that are either Low 0v or High 5v.

The PWM signal plot looks something like as shown in the diagram below. As you know from elementary physics that a frequency of a signal is a measure of how many cycles are completed each second. Which means the duty cycle can be easily determined using the following formula. Thus our microcontroller can now, seemingly not exactly, output analog values between v.

You can think of it as changing the duty cycle of a PWM signal corresponds to changing the average effective voltage of the output line. Here is the logic Block diagram for the PWM mode as found in the datasheet 8.

Or equivalently this hand-drawn version for the same diagram. As you might have noticed in the above diagram, the operation of the ccp module in PWM mode goes as follows.

Timer2 should be turned ON with the pre-specified prescaler value. And it stays low till the end of the current PWM cycle. At the beginning of a new cycle, the output latch is set again to High and so on. II- Timer2 postscaler :. The Timer2 postscaler is not used in the determination of the PWM frequency.

The postscaler could be used to have a servo update rate at a different frequency than the PWM output. III- Duty Cycle value :. This double-buffering is essential for glitch-free PWM operation.

## What is PWM and how does it work?

V- PWM Resolution :. Up to bit resolution is available. The typical resolution in bits for a specific PWM frequency, with a specific Prescaler ratio PS, for a system running at Fosc clock rate is given by the equation down below.

Here is the step-by-step procedure that you should follow in order to operate the CCP module in the PWM mode to generate the PWM output signal with your desired duty cycle and frequency. Step3 — Determine the PWM frequency. After substitution, our equation will be as follows. Solving for PR2 will yield the following result. Solving for PR2 will now yield the following result.

Step4 — Write to the PR2 Register. Step5 — Set the prescaler of Timer2. This step involves both calculating and writing the Bit DC value as discussed earlier.

And solve for the Bit value between the. This is done as shown below. Step7 — Turn ON Timer2. If you have some issues doing so, you can always refer to the previous tutorial using the link below. And if you also find troubles creating this file, you can always refer to the previous tutorial using the link below. Now, open the main. And also configure the PWM output frequency to be 2kHz.

The rest of the code will reside normally in the main routine.Digital signals have two positions: on or off, interpreted in shorthand as 1 or 0. Analog signals, on the other hand, can be on, off, half-way, two-thirds the way to on, and an infinite number of positions between 0 and 1 either approaching 1 or descending down to zero. Often engineers will translate that analog input into digital input for the microcontroller MCU by using an analog-to-digital converter.

But what about outputs? PWM is a way to control analog devices with a digital output. Another way to put it is that you can output a modulating signal from a digital device such as an MCU to drive an analog device. PWM is not true analog output, however. Figure 1: An example of a PWM signal shown at several duty cycles and a high voltage level of 5 volts. The red line is the average voltage that the driven device e. Source: Timothy Hirzel.

An example would be to apply full voltage to a motor or lamp for fractions of a second or pulse the voltage to the motor at intervals that made the motor or lamp do what you wanted it to do.

### Three Ways To Read A PWM Signal With Arduino

In reality, the voltage is being applied and then removed many times in an interval, but what you experience is an analog-like response. If you have ever jogged a box fan by applying power intermittently, you will experience a PWM response. The fan and its motor do not stop instantly due to inertia, and so by the time you re-apply power it has only slowed a bit.

Therefore, you do not experience an abrupt stop in power if a motor is driven by PWM. In this case, the pulse width and corresponding duty cycle change so that the average voltage looks more like an analog output that is not in a steady state such as shown in Figure 1. A device that is driven by PWM ends up behaving like the average of the pulses.

If you want the motor to go faster, you can drive the PWM output to a higher duty cycle. The higher the frequency of high pulses, the higher the average voltage and the faster the fan motor will spin. In electronics, we would identify frequency as cycles per second, or Hertz Hz. You have increased the speed of the fan.

You might have gathered by now that PWM, duty cycle, and frequency are interrelated. We use duty cycle and frequency to describe the PWM, and we often talk about frequency in reference to speed. For example, a variable frequency drive motor produces a response like analog device in the real world. The separate pulses that the VFD motor gets are not discernable to us; as far as we can see, the pulses are so fast usually somewhere in the milliseconds that by real world standards it just seems like a motor ramping up.

The duty cycle can change to affect the average voltage that the motor experiences. The frequency of the cycles can increase. The pulse can even be increased in length. Pulse width is directly related to duty cycle, so if you decide to increase the width of a pulse, you are just altering the duty cycle. MCUs are digital. An example of something that can create a true analog output would be a transducer something that directly translates physical phenomenon to an analog signal.

But transducers are another analog discussion.The option of controlling the fan speed and the satisfaction of silent computing were not always present when it comes to personal computers. The early x86 computers did not have active cooling because not much heat was generated, right until the introduction of the first models. From that time and up until now, the computer power consumption and thermal dissipation have grown exponentially, as well as their performance. It was followed by the use of ordinary resistors to slow the fans down, fans equipped with thermal resistors, various potentiometers for a wide range manual speed control, etc.

But nowadays, if you want to control the speed of your fans and pumps, PWM control is the way to go. Every mainstream motherboard that leaves the factory today is equipped with at least one 4-pin PWM header. However, even today, many years after the introduction of PWM inthere are users that are still not familiar with its advantages. And worse, there are serious companies out there that make advanced and well-designed fans with old-fashioned 3-pin connectors. Therefore, we will explain what PWM actually is, how it controls the speed of fans and pumps, and we will also show you an example of a PWM profile in one of the software provided by the motherboard manufacturers.

By the number of wires — pins that a fan has — we can distinguish three main types of connections. A signal is sent via this third wire with a certain frequency that is proportional to the fan speed, expressed in RPM revolutions per minute. The third type of fans that use four wires are PWM fans and that is what will be discussed in this article, along with PWM pumps. PWM Pulse Width Modulation or modulation with the width of an impulse, is a widespread term in the world of electrical engineering.

It has a broad range of application, like in the field of telecommunications, audio equipment, servo motors, etc. Interesting for us enthusiasts is the application of PWM in voltage regulation. Some of you probably already know the principle on which pulse width modulation PWM works, but nevertheless, we will explain how it actually controls the speed of a fan or a pump.

In short, PWM operates like a switch which constantly cycles on and off, thereby regulating the amount of power the fan or pump motor gains. To have a better understanding how this works, take a look at the chart bellow. So, the motor is being fed impulses of power. Imagine it the same way as if you were to turn the wheel with your hand. You can push the wheel every 5 seconds with the same amount of force, and you will keep the wheel spinning.

In that case, you would notice that the wheel is spinning a bit faster, and in almost the same way is how the Pulse Width Modulation works. The speed of the motor, i. It is important to know that there is no voltage regulation involved here, and by using PWM regulation the motor is constantly being fed 12 volts. For that reason, the 4-pin motherboard header should be used only for one fan, or eventually two, by using the Y-splitter. Pumps for water cooling have significantly bigger power consumption, so the power is mostly hooked up to the molex connector, and the other two tach and PWM wires are connected to the motherboard header for PWM control and speed readout.

More quality fans have their own special IC driver chips within the motor hub that generate a sloped PWM signal instead of a flat square one. Flat square signals tend to create unpleasant clicking noises when the fan runs at low speeds. The use of special ICs makes sure that the motor is powered on more gently each time an impulse is given.

Why is PWM so important? At these speeds, the fans are dead silent, and some fans can even be turned off completely via PWM regulation. Since the fans are getting 12 volts all the time, you can use special fan hub splitters that will send one PWM signal to all of the connected fans or even pumps.

This way, all of your fans and pumps will work in harmony. Simple and very efficient way to get a silent computer, of course, if you are equipped with quality PWM fans and quality PWM pumps.

The high static pressure fan, designed and built primarily for highest-performance computer liquid cooling systems. It has a wide operational range and great performance in both case and water cooling. Pump motor optionally with and without top, and RGB.Printable PDF.

Pulse width modulation PWM is a powerful technique for controlling analog circuits with a processor's digital outputs. PWM is employed in a wide variety of applications, ranging from measurement and communications to power control and conversion. An analog signal has a continuously varying value, with infinite resolution in both time and magnitude. A nine-volt battery is an example of an analog device, in that its output voltage is not precisely 9V, changes over time, and can take any real-numbered value.

Similarly, the amount of current drawn from a battery is not limited to a finite set of possible values. Analog voltages and currents can be used to control things directly, like the volume of a car radio.

In a simple analog radio, a knob is connected to a variable resistor. As you turn the knob, the resistance goes up or down. As that happens, the current flowing through the resistor increases or decreases. This changes the amount of current driving the speakers, thus increasing or decreasing the volume. An analog circuit is one, like the radio, whose output is linearly proportional to its input. As intuitive and simple as analog control may seem, it is not always economically attractive or otherwise practical.

For one thing, analog circuits tend to drift over time and can, therefore, be very difficult to tune. Precision analog circuits, which solve that problem, can be very large, heavy just think of older home stereo equipmentand expensive. Analog circuits can also get very hot; the power dissipated is proportional to the voltage across the active elements multiplied by the current through them. Analog circuitry can also be sensitive to noise.

Because of its infinite resolution, any perturbation or noise on an analog signal necessarily changes the current value. By controlling analog circuits digitally, system costs and power consumption can be drastically reduced.

In a nutshell, PWM is a way of digitally encoding analog signal levels. Through the use of high-resolution countersthe duty cycle of a square wave is modulated to encode a specific analog signal level. The PWM signal is still digital because, at any given instant of time, the full DC supply is either fully on or fully off.

The voltage or current source is supplied to the analog load by means of a repeating series of on and off pulses.Pulse width modulation PWMor pulse-duration modulation PDMis a method of reducing the average power delivered by an electrical signal, by effectively chopping it up into discrete parts.

The average value of voltage and current fed to the load is controlled by turning the switch between supply and load on and off at a fast rate. The longer the switch is on compared to the off periods, the higher the total power supplied to the load.

Along with MPPT maximum power point trackingit is one of the primary methods of reducing the output of solar panels to that which can be utilized by a battery. The PWM switching frequency has to be high enough not to affect the load, which is to say that the resultant waveform perceived by the load must be as smooth as possible. The rate or frequency at which the power supply must switch can vary greatly depending on load and application. The main advantage of PWM is that power loss in the switching devices is very low.

When a switch is off there is practically no current, and when it is on and power is being transferred to the load, there is almost no voltage drop across the switch. Power loss, being the product of voltage and current, is thus in both cases close to zero. PWM has also been used in certain communication systems where its duty cycle has been used to convey information over a communications channel.

The term duty cycle describes the proportion of 'on' time to the regular interval or 'period' of time; a low duty cycle corresponds to low power, because the power is off for most of the time.

Here is a pictorial that illustrates these three scenarios:. Some machines such as a sewing machine motor require partial or variable power. In the past, control such as in a sewing machine's foot pedal was implemented by use of a rheostat connected in series with the motor to adjust the amount of current flowing through the motor. It was an inefficient scheme, as this also wasted power as heat in the resistor element of the rheostat, but tolerable because the total power was low.

This mechanism also needed to be able to drive motors for fans, pumps and robotic servosand needed to be compact enough to interface with lamp dimmers. PWM emerged as a solution for this complex problem. Of note, for about a century, some variable-speed electric motors have had decent efficiency, but they were somewhat more complex than constant-speed motors, and sometimes required bulky external electrical apparatus, such as a bank of variable power resistors or rotating converters such as the Ward Leonard drive.

Pulse-width modulation uses a rectangular pulse wave whose pulse width is modulated resulting in the variation of the average value of the waveform.

The above expression then becomes:. The simplest way to generate a PWM signal is the intersective method, which requires only a sawtooth or a triangle waveform easily generated using a simple oscillator and a comparator. When the value of the reference signal the red sine wave in figure 2 is more than the modulation waveform bluethe PWM signal magenta is in the high state, otherwise it is in the low state. In the use of delta modulation for PWM control, the output signal is integrated, and the result is compared with limits, which correspond to a Reference signal offset by a constant.The content is shown in another available language.

Your browser may include features that can help translate the text. This content is not available in your preferred language. Reported In. Reported In shows products that are verified to work for the solution described in this article. This solution might also apply to other similar products or applications. What is a pulse width modulation PWM signal and what is it used for?

A PWM signal consists of two main components that define its behavior: a duty cycle and a frequency. The duty cycle describes the amount of time the signal is in a high on state as a percentage of the total time of it takes to complete one cycle. The frequency determines how fast the PWM completes a cycle i.

By cycling a digital signal off and on at a fast enough rate, and with a certain duty cycle, the output will appear to behave like a constant voltage analog signal when providing power to devices. Open a service request. Purchase or renew support services. Was this information helpful? Not Helpful.Track My Order. Frequently Asked Questions.

International Shipping Info. Send Email. Mon-Fri, 9am to 12pm and 1pm to 5pm U. Mountain Time:. Chat With Us. Pulse width modulation is used in a variety of applications including sophisticated control circuitry. We can accomplish a range of results in both applications because pulse width modulation allows us to vary how much time the signal is high in an analog fashion.

What is Pulse Width Modulation? How to generate PWM signal ? Pulse Width Modulation Explained

While the signal can only be high usually 5V or low ground at any time, we can change the proportion of time the signal is high compared to when it is low over a consistent time interval. Robotic claw controlled by a servo motor using pulse-width modulation. When the signal is high, we call this "on time". To describe the amount of "on time"we use the concept of duty cycle. Duty cycle is measured in percentage. The percentage duty cycle specifically describes the percentage of time a digital signal is on over an interval or period of time.

This period is the inverse of the frequency of the waveform. Here is a graph that illustrates these three scenarios:. With an RGB red green blue LEDyou can control how much of each of the three colors you want in the mix of color by dimming them with various amounts. If all three are on in equal amounts, the result will be white light of varying brightness.

Blue equally mixed with green will get teal. The frequency of the square wave does need to be sufficiently high enough when controlling LEDs to get the proper dimming effect. You can also use pulse width modulation to control the angle of a servo motor attached to something mechanical like a robot arm. Servos have a shaft that turns to specific position based on its control line. Our servo motors have a range of about degrees.

With a 1. With a 1 ms pulse, the servo will be at the 0 degree position, and with a 2 ms pulse, the servo will be at degrees. You can obtain the full range of motion by updating the servo with an value in between. PWM used to hold a servo motor at 90 degrees relative to its bracket.

Pulse width modulation is used in a variety of applications particularly for control. You already know it can be used for the dimming of LEDs and controlling the angle of servo motors and now you can begin to explore other possible uses. If you feel lost, feel free to check out the SparkFun Inventor's Kit which has examples using pulse width modulation.

If you're ready to jump into coding immediately and have an Arduino, look at the PWM coding example here. See our Engineering Essentials page for a full list of cornerstone topics surrounding electrical engineering. Take me there! Need Help? Mountain Time: Chat With Us. Shopping Cart 0 items.