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# Why pwm is required?

In this tutorial, I will cover the following :

Pulse Width Modulation(PWM) is a digital technology that uses the amount of power delivered to a device that can be changed. It generates analogue signals by using a digital source. A PWM signal is basically a square wave which is switched between on and off state. The duty cycle and frequency of a PWM signal determine its behaviour.

The duty cycle of the PWM signal refers to the ratio of the time that the signal is in a high(on) state over the total time it takes to complete one cycle. It is commonly expressed as a percentage or a ratio.

A 50% duty cycle means that the high state takes half of the time and the low state takes the other half of the time, this is the same as an ideal square wave. If this ratio is greater than 50%, the logic high signal takes a longer time than logic low, vice versa. Thus, a 100% duty cycle means the signal is always on(full-scale), and the 0% duty cycle means the signal is always off(grounding).

A period is equal to the time this signal completes a one-and-off cycle. The frequency is the number of times a periodic change is completed per unit time and it is the inverse of the period. It determines the speed at which the PWM completes one cycle, which means the speed at which the signal switches between high and low states. If we turn the digital signal on and off repeatedly with a high enough frequency, the output will behave like an analogue signal with a constant voltage.

For PWM, adjusting the brightness of the screen does not rely on the power but by alternating on and off of the screen. When the PWM dimming screen is lit, it does not continuously emit light, but it constantly lights up and turns off the screen. If this changes fast enough, our eyes treat is as always on but with different brightness based on different duty cycles. The larger the duty cycle, the brighter the screen.

There are other applications that use PWM technology, including:

PWM can be implemented in various ways on Arduino. On Seeeduino board, there are 6 pins(i.e. pin 3, 5, 6, 9, 10, 11 ) which can output a PWM wave with analogWrite() function. Calling the AnalogWrite() function allows a stable square wave with a specified duty cycle to be generated on the PWM pins. Generally, the frequency of these pins are about 490Hz, and the pin 5 and 6 of Seeeduino or its similar boards have the frequency of 980Hz.

The output voltage from Arduino pins are 5V, and different duty cycles output different voltage levels as stated below:

To control the brightness of an LED with Arduino with the PWM technique. You can follow the example below:

Hardware Connection

Software

analogWrite() Function Syntax:

analogWrite ( pin , value ) ;

The value representing the duty cycle, and the number is between 0(off) and 255(on).

You can change ‘255’ to any number between 0~255 for different outputs, or you can modify the code to change the value continuously.

Have you ever felt anxious because of the limited number of development board PWM output interfaces? Don’t worry! The Grove – 16-Channel PWM Driver is based on NXP PCA9685, which is a 16-Channel 12bit I2C PWM driver. This PCA9685 16-Channel 12bit I2C PWM driver board can drive up to 16 servos with external power supply.

Based on the features of NXP PCA9685, this PWM driver board can well meet the needs of multi-channel PWM projects, such as a hexapod walker, MarsCar. Additionally, you can use this board as a LED controller. You can easily control this driver board through the I2C Grove interface.

Motor Pack for Arduino is a perfect kit for you to learn motor with Arduino. Whether your project requires a DC motor, a stepper motor, or a steering gear, all of them can be found in this kit! But do you know how to use PWM to control the motor?

For a DC motor, when the load (torque) of the motor is constant, the speed is proportional to the power supply voltage. As discussed above, the output voltage level is determined by the duty cycle of PWM, thus the PWM can be used to control the speed of the motor.

Hardware Connection

Similar hardware connection would apply to Motor as well.

Software

analogWrite() Function Syntax:

analogWrite ( pin , value ) ;

The value representing the duty cycle, and the number is between 0(off) and 255(on).

You can change ‘255’ to any number between 0~255 for different outputs, or you can modify the code to change the value continuously.

And that’s all on PWM! Have you learnt something new through this blog? Hope that we managed to help you with your projects, happy tinkering!

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Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a method of controlling the average power delivered by an electrical signal. The average value of voltage (and current) fed to the load is controlled by switching the supply between 0 and 100% at a rate faster than it takes the load to change significantly. The longer the switch is on, the higher the total power supplied to the load. Along with maximum power point tracking (MPPT), it is one of the primary methods of reducing the output of solar panels to that which can be utilized by a battery.[1] PWM is particularly suited for running inertial loads such as motors, which are not as easily affected by this discrete switching. The goal of PWM is to control a load; however, the PWM switching frequency must be selected carefully in order to smoothly do so.

The PWM switching frequency can vary greatly depending on load and application. For example, switching only has to be done several times a minute in an electric stove; 100 or 120 Hz (double of the utility frequency) in a lamp dimmer; between a few kilohertz (kHz) and tens of kHz for a motor drive; and well into the tens or hundreds of kHz in audio amplifiers and computer power supplies. Choosing a switching frequency that is too high for the application results in smooth control of the load, but may cause premature failure of the mechanical control components. Selecting a switching frequency that is too low for the application causes oscillations in the load. 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 also works well with digital controls, which, because of their on/off nature, can easily set the needed duty cycle. PWM has also been used in certain communication systems where its duty cycle has been used to convey information over a communications channel.

In electronics, many modern microcontrollers (MCUs) integrate PWM controllers exposed to external pins as peripheral devices under firmware control by means of internal programming interfaces. These are commonly used for direct current (DC) motor control in robotics, switched-mode power supply regulation, and other applications.

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. Duty cycle is expressed in percent, 100% being fully on. When a digital signal is on half of the time and off the other half of the time, the digital signal has a duty cycle of 50% and resembles a "square" wave. When a digital signal spends more time in the on state than the off state, it has a duty cycle of >50%. When a digital signal spends more time in the off state than the on state, it has a duty cycle of <50%. Here is a pictorial that illustrates these three scenarios:

The Corliss steam engine was patented in 1849. It used pulse width modulation to control the intake valve of a steam engine cylinder. A centrifugal governor was used to provide automatic feedback,

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. While the rheostat was one of several methods of controlling power (see autotransformers and Variac for more info), a low cost and efficient power switching/adjustment method was yet to be found. This mechanism also needed to be able to drive motors for fans, pumps and robotic servos, and needed to be compact enough to interface with lamp dimmers. PWM emerged as a solution for this complex problem.

The Philips, N. V. company designed an optical scanning system (published in 1946) for variable area film soundtrack which produced the PWM. It was intended for reducing noise when playing back a film soundtrack. The proposed system had a threshold between "white" and "black" parts of soundtrack.[2]

One early application of PWM was in the Sinclair X10, a 10 W audio amplifier available in kit form in the 1960s. At around the same time PWM started to be used in AC motor control.[3]

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. If we consider a pulse waveform f ( t ) {\displaystyle f(t)} , with period T {\displaystyle T} , low value y min {\displaystyle y_{\text{min}}} , a high value y max {\displaystyle y_{\text{max}}} and a duty cycle D (see figure 1), the average value of the waveform is given by:

As f ( t ) {\displaystyle f(t)} is a pulse wave, its value is y max {\displaystyle y_{\text{max}}} for 0 < t < D ⋅ T {\displaystyle 0

This latter expression can be fairly simplified in many cases where y min = 0 {\displaystyle y_{\text{min}}=0} as y ¯ = D ⋅ y max {\displaystyle {\bar {y}}=D\cdot y_{\text{max}}} . From this, the average value of the signal ( y ¯ {\displaystyle {\bar {y}}} ) is directly dependent on the duty cycle D.

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 (blue), the 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. Every time the integral of the output signal reaches one of the limits, the PWM signal changes state.[4] Figure 3

In delta-sigma modulation as a PWM control method, the output signal is subtracted from a reference signal to form an error signal. This error is integrated, and when the integral of the error exceeds the limits, the output changes state. Figure 4

Space vector modulation is a PWM control algorithm for multi-phase AC generation, in which the reference signal is sampled regularly; after each sample, non-zero active switching vectors adjacent to the reference vector and one or more of the zero switching vectors are selected for the appropriate fraction of the sampling period in order to synthesize the reference signal as the average of the used vectors.

Direct torque control is a method used to control AC motors. It is closely related with the delta modulation (see above). Motor torque and magnetic flux are estimated and these are controlled to stay within their hysteresis bands by turning on a new combination of the device's semiconductor switches each time either signal tries to deviate out of its band.

Many digital circuits can generate PWM signals (e.g., many microcontrollers have PWM outputs). They normally use a counter that increments periodically (it is connected directly or indirectly to the clock of the circuit) and is reset at the end of every period of the PWM. When the counter value is more than the reference value, the PWM output changes state from high to low (or low to high).[5] This technique is referred to as time proportioning, particularly as time-proportioning control[6] – which proportion of a fixed cycle time is spent in the high state.

The incremented and periodically reset counter is the discrete version of the intersecting method's sawtooth. The analog comparator of the intersecting method becomes a simple integer comparison between the current counter value and the digital (possibly digitized) reference value. The duty cycle can only be varied in discrete steps, as a function of the counter resolution. However, a high-resolution counter can provide quite satisfactory performance.

Three types of pulse-width modulation (PWM) are possible:

The resulting spectra (of the three cases) are similar, and each contains a dc component—a base sideband containing the modulating signal and phase modulated carriers at each harmonic of the frequency of the pulse. The amplitudes of the harmonic groups are restricted by a sin ⁡ x / x {\displaystyle \sin x/x} envelope (sinc function) and extend to infinity. The infinite bandwidth is caused by the nonlinear operation of the pulse-width modulator. In consequence, a digital PWM suffers from aliasing distortion that significantly reduce its applicability for modern communication systems. By limiting the bandwidth of the PWM kernel, aliasing effects can be avoided.[7]

On the contrary, the delta modulation is a random process that produces continuous spectrum without distinct harmonics.

The process of PWM conversion is non-linear and it is generally supposed that low pass filter signal recovery is imperfect for PWM. The PWM sampling theorem[8] shows that PWM conversion can be perfect. The theorem states that "Any bandlimited baseband signal within ±0.637 can be represented by a pulsewidth modulation (PWM) waveform with unit amplitude. The number of pulses in the waveform is equal to the number of Nyquist samples and the peak constraint is independent of whether the waveform is two-level or three-level."

PWM is used to control servomechanisms; see servo control.

In telecommunications, PWM is a form of signal modulation where the widths of the pulses correspond to specific data values encoded at one end and decoded at the other.

Pulses of various lengths (the information itself) will be sent at regular intervals (the carrier frequency of the modulation).

The inclusion of a clock signal is not necessary, as the leading edge of the data signal can be used as the clock if a small offset is added to each data value in order to avoid a data value with a zero length pulse.

PWM can be used to control the amount of power delivered to a load without incurring the losses that would result from linear power delivery by resistive means. Drawbacks to this technique are that the power drawn by the load is not constant but rather discontinuous (see Buck converter), and energy delivered to the load is not continuous either. However, the load may be inductive, and with a sufficiently high frequency and when necessary using additional passive electronic filters, the pulse train can be smoothed and average analog waveform recovered. Power flow into the load can be continuous. Power flow from the supply is not constant and will require energy storage on the supply side in most cases. (In the case of an electrical circuit, a capacitor to absorb energy stored in (often parasitic) supply side inductance.)

High frequency PWM power control systems are easily realisable with semiconductor switches. As explained above, almost no power is dissipated by the switch in either on or off state. However, during the transitions between on and off states, both voltage and current are nonzero and thus power is dissipated in the switches. By quickly changing the state between fully on and fully off (typically less than 100 nanoseconds), the power dissipation in the switches can be quite low compared to the power being delivered to the load.

Modern semiconductor switches such as MOSFETs or insulated-gate bipolar transistors (IGBTs) are well suited components for high-efficiency controllers. Frequency converters used to control AC motors may have efficiencies exceeding 98%. Switching power supplies have lower efficiency due to low output voltage levels (often even less than 2 V for microprocessors are needed) but still more than 70–80% efficiency can be achieved.

Variable-speed computer fan controllers usually use PWM, as it is far more efficient when compared to a potentiometer or rheostat. (Neither of the latter is practical to operate electronically; they would require a small drive motor.)

Light dimmers for home use employ a specific type of PWM control. Home-use light dimmers typically include electronic circuitry which suppresses current flow during defined portions of each cycle of the AC line voltage. Adjusting the brightness of light emitted by a light source is then merely a matter of setting at what voltage (or phase) in the AC half-cycle the dimmer begins to provide electric current to the light source (e.g. by using an electronic switch such as a triac). In this case the PWM duty cycle is the ratio of the conduction time to the duration of the half AC cycle defined by the frequency of the AC line voltage (50 Hz or 60 Hz depending on the country).

These rather simple types of dimmers can be effectively used with inert (or relatively slow reacting) light sources such as incandescent lamps, for example, for which the additional modulation in supplied electrical energy which is caused by the dimmer causes only negligible additional fluctuations in the emitted light. Some other types of light sources such as light-emitting diodes (LEDs), however, turn on and off extremely rapidly and would perceivably flicker if supplied with low frequency drive voltages. Perceivable flicker effects from such rapid response light sources can be reduced by increasing the PWM frequency. If the light fluctuations are sufficiently rapid (faster than the flicker fusion threshold), the human visual system can no longer resolve them and the eye perceives the time average intensity without flicker.

In electric cookers, continuously variable power is applied to the heating elements such as the hob or the grill using a device known as a simmerstat. This consists of a thermal oscillator running at approximately two cycles per minute and the mechanism varies the duty cycle according to the knob setting. The thermal time constant of the heating elements is several minutes, so that the temperature fluctuations are too small to matter in practice.

PWM is also used in efficient voltage regulators. By switching voltage to the load with the appropriate duty cycle, the output will approximate a voltage at the desired level. The switching noise is usually filtered with an inductor and a capacitor.

One method measures the output voltage. When it is lower than the desired voltage, it turns on the switch. When the output voltage is above the desired voltage, it turns off the switch.

Varying the duty cycle of a pulse waveform in a synthesis instrument creates useful timbral variations. Some synthesizers have a duty-cycle trimmer for their square-wave outputs, and that trimmer can be set by ear; the 50% point (true square wave) was distinctive, because even-numbered harmonics essentially disappear at 50%. Pulse waves, usually 50%, 25%, and 12.5%, make up the soundtracks of classic video games. The term PWM as used in sound (music) synthesis refers to the ratio between the high and low level being secondarily modulated with a low frequency oscillator. This gives a sound effect similar to chorus or slightly detuned oscillators played together. (In fact, PWM is equivalent to the sum of two sawtooth waves with one of them inverted.)[10]

A new class of audio amplifiers based on the PWM principle is becoming popular. Called class-D amplifiers, they produce a PWM equivalent of the analog input signal which is fed to the loudspeaker via a suitable filter network to block the carrier and recover the original audio. These amplifiers are characterized by very good efficiency figures (≥ 90%) and compact size/light weight for large power outputs. For a few decades, industrial and military PWM amplifiers have been in common use, often for driving servo motors. Field-gradient coils in MRI machines are driven by relatively high-power PWM amplifiers.

Historically, a crude form of PWM has been used to play back PCM digital sound on the PC speaker, which is driven by only two voltage levels, typically 0 V and 5 V. By carefully timing the duration of the pulses, and by relying on the speaker's physical filtering properties (limited frequency response, self-inductance, etc.) it was possible to obtain an approximate playback of mono PCM samples, although at a very low quality, and with greatly varying results between implementations.

In more recent times, the Direct Stream Digital sound encoding method was introduced, which uses a generalized form of pulse-width modulation called pulse-density modulation, at a high enough sampling rate (typically in the order of MHz) to cover the whole acoustic frequencies range with sufficient fidelity. This method is used in the SACD format, and reproduction of the encoded audio signal is essentially similar to the method used in class-D amplifiers.

SPWM (Sine–triangle pulse width modulation) signals are used in micro-inverter design (used in solar and wind power applications). These switching signals are fed to the FETs that are used in the device. The device's efficiency depends on the harmonic content of the PWM signal. There is much research on eliminating unwanted harmonics and improving the fundamental strength, some of which involves using a modified carrier signal instead of a classic sawtooth signal[11][12][13] in order to decrease power losses and improve efficiency. Another common application is in robotics where PWM signals are used to control the speed of the robot by controlling the motors.

PWM techniques would typically be used to make some indicator (like a LED) "soft blink". The light will slowly go from dark to full intensity, and slowly dimmed to dark again. Then it repeats. The period would be several soft-blinks per second up to several seconds for one blink. An indicator of this type would not disturb as much as a "hard-blinking" on/off indicator. The indicator lamp on the Apple iBook G4, PowerBook 6,7 (2005) was of this type. This kind of indicator is also called "pulsing glow", as opposed to calling it "flashing".

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Because the PWM signal controls the average voltage delivered to the motor, you can reduce the voltage when less power is needed, resulting in less energy consumption. This can lead to significant energy savings over time in OEM applications, especially in applications where the motor runs for extended periods of time.

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Holistic Nursing
• Cheap to make.
• Low power consumption.
• Efficiency up to 90 %
• A signal can be separated very easily at demodulation and noise can be also separated easily.
• High power handling capacity.
• Can utilize very high frequency.
• Little heat whilst working.
• Noise interference is less.
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●     Learn about pulse width modulation (PWM).

●     Gain a greater understanding of PWM as a controlling method.

●     Get a better understanding of the effects of duty cycle and frequency in PWM.

The mean output signal of a pulse width modulation signal at the input.

In electronics, modulation is the application of a controlling or altering influence on something. We also refer to it as a variation in the pitch, strength, or tone of a frequency, like in the human voice.

However, in terms of applications, we typically encounter modulation techniques in use for control of devices like DC motors or LEDs. In cases such as these, the technique is called pulse width modulation (PWM).

As stated previously, modulation refers to the ability to exert control over a device or system. Therefore, methods such as this exist in a myriad of applications within the field of electronics. One of the more common uses for modulation as a control method is PWM.

We encounter the extensive use of PWM due to its adaptive nature. PWM is a technique that mitigates the average amount of deliverable power of an applied electrical signal. Moreover, the process is achieved by effectively chopping up the signal into distinct parts. In terms of functional operation, PWM achieves this control by controlling the average current and voltage it delivers to the load. This method is accomplished by rapidly turning the switch between the load and the source, on and off.

However, if we compare on and off periods of the switch, an increase in on-time versus the off-time increases the total power supplied to the load. In general, this method of control has many beneficial applications. For example, PWM paired with maximum power point tracking (MPPT) is one of the principal methods for reducing a solar panel's output to facilitate its use by a battery.

Overall, PWM is principally suited for running inertial devices like motors, which are not as quickly affected by this distinct switching. This is also equally true for LEDs with PWM because of the linear fashion in which their input voltage affects their functionality. However, the PWM switching frequency needs to be high enough not to affect the load, yet the resulting waveform that the load perceives should also be smooth.

Typically, the frequency in which the power supply must switch will vary extensively depending on the device and its application. For example, the switching has to be done several times a minute in an electric stove and well into the tens or hundreds of kHz for PC power supplies and audio amplifiers. One of the significant advantages of using PWM is that power loss in the switching devices is substantially low. In fact, during the off phase of a switch, there is virtually no current. Also, during the on phase of a switch, there is practically no drop in voltage across the switch while transferring power to its load.

Since power loss is a consequence of both voltage and current, this translates into virtually zero loss in power for PWM. Moreover, PWM is perfectly suited for digital controls, due to the nature of digital technology (i.e., 1's and 0's, or ON and OFF states). In general, the intrinsic nature of digital technology lends itself effortlessly to PWM's functionality, and thus, it is easy to set the necessary duty cycle.

A PWM signal is a method for creating digital pulses to control analog circuits. There are two primary components that define a PWM signal's behavior:

About the duty cycle, while the signal is high, we refer to it as ON, and the duty cycle describes the amount of time a signal is in its ON-state. We measure or quantify a duty cycle as a percentage. This percentage represents the specific time a digital signal is ON during a period (interval), and this interval is the inverse of the waveform frequency.

For example, a digital signal that spends half of the time in an ON-state and half the time in an OFF-state will have a duty cycle of 50%, i.e., an ideal square wave. A digital signal that spends three-quarters of the time in an ON-state and one-quarter of the time in an OFF-state will have a duty cycle of 75%.

We discussed the vast array of applications that ideally suit PWM's functionality, including LEDs and motors (servo). Since frequency is a primary component of the PWM technique, it is understandable that frequency affects PWM's ability to exert control within an application. Therefore, the square wave frequency does need to be sufficiently high enough if controlling LEDs, for example, to get the proper dimming effect.

As an example, a duty cycle of 20% at 1 Hz will be noticeable to the human eye that an LED is turning OFF and ON. Whereas, a duty cycle of 20% at 100 Hz or higher will merely exhibit a slightly less dim light output.

As I am sure you are aware, we can utilize PWM to control motors (servo). We can also use it to control a servo motor's angle. In terms of applications, this is beneficial when we attach it to a mechanical device like a robotic arm in an assembly or manufacturing environment. This is ideal because a servo utilizes a shaft which turns to a specific position depending on its control line.

A frequency or period is specific to controlling a particular servo. Typically, a servo motor anticipates an update every 20 ms with a pulse between 1 ms and 2 ms. This equates to a duty cycle of 5% to 10% at 50 Hz. Now, if the pulse is at 1.5 ms, the servo motor will be at 90-degrees, at 1 ms, 0-degrees, and at 2 ms, 180 degrees. In summary, by updating the servo with a value between 1 ms and 2ms, we can obtain a full range of motion.

PWM is also currently in specific communication systems, and its duty cycle is in use to convey information over communications channels. Overall, PWM is a methodology or technique to generate low-frequency output signals from high-frequency pulses.

By quickly switching the output voltage of an inverter leg between the upper and lower voltages (DC rail), the low-frequency output basically becomes the average voltage over the switching period.

PWM as a controlling technique is ideally suited to a vast array of applications. Along with its duty cycle, the PWM frequency is the foundation of its functionality as a controlling method.

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