and also plz plz rate my instructable well
Hi every one.Today i'll show you how to make a PWM(pulse width modulation) out of a very famous chip 555(lm,ne any one will do) with some other parts offcourse.This is really simple and it is very handy if you want to control your leds,light bulb,servo motor or dc motor(brushless also works).
My pwm can only change the duty cyle from 10% to 90% it cant do nothing more!
Step 1: What Is PWM
Step 2: Types of Pwm
1. The pulse center may be fixed in the center of the time window and both edges of the pulse moved to compress or expand the width.
2. The lead edge can be held at the lead edge of the window and the tail edge modulated.
3. The tail edge can be fixed and the lead edge modulated.
Three types of PWM signals (blue): leading edge modulation (top), trailing edge modulation (middle) and centered pulses (both edges are modulated, bottom). The green lines are the sawtooth signals used to generate the PWM waveforms using the intersective method.
Step 3: How Can PWM Help Us???
PWM can be used to reduce the total amount of power delivered to a load without losses normally incurred when a power source is limited by resistive means. This is because the average power delivered is proportional to the modulation duty cycle. With a sufficiently high modulation rate, passive electronic filters can be used to smooth the pulse train and recover an average analog waveform.
High frequency PWM power control systems are easily realisable with semiconductor switches. The discrete on/off states of the modulation are used to control the state of the switch(es) which correspondingly control the voltage across or current through the load. The major advantage of this system is the switches are either off and not conducting any current, or on and have (ideally) no voltage drop across them. The product of the current and the voltage at any given time defines the power dissipated by the switch, thus (ideally) no power is dissipated by the switch. Realistically, semiconductor switches such as MOSFETs or BJTs are non-ideal switches, but high efficiency controllers can still be built.
PWM is also often used to control the supply of electrical power to another device such as in speed control of electric motors, volume control of Class D audio amplifiers or brightness control of light sources and many other power electronics applications. For example, 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 cycle the dimmer begins to provide electrical current to the light source (e.g. by using an electronic switch such as a triac). In this case the PWM duty cycle is 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, the human visual system can no longer resolve them and the eye perceives the time average intensity without flicker (see flicker fusion threshold).
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.
Variable-speed fan controllers for computers usually use PWM, as it is far more efficient when compared to a potentiometer.
Audio effects and amplification:
PWM is sometimes used in sound synthesis, in particular subtractive synthesis, as it gives a sound effect similar to chorus or slightly detuned oscillators played together. (In fact, PWM is equivalent to the difference of two sawtooth waves. ) The ratio between the high and low level is typically modulated with a low frequency oscillator, or LFO.
A new class of audio amplifiers based on the PWM principle is becoming popular. Called "Class-D amplifiers", these amplifiers 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 (e 90%) and compact size/light weight for large power outputs.
Historically, a crude form of PWM has been used to play back PCM digital sound on the PC speaker, which is only capable of outputting two sound levels. 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.
Speaker:Using pwm it is possible to modulate arc(plasma) and if it is in the hearing range,it can be used as a speaker.Such speaker are used in Hi-Fi sound system as tweeter
Step 4: Thing You Will Need
1.NE555,LM555 or 7555(cmos)
2.two diodes 1n4148 is recomended but you can also use 1n40xx series diodes
3.100k pot(volume control pots are good for this circuit)
4.100nf green cap
5.220pf ceramic cap
Step 5: Building It $$$$
there is two video.you can watch how pwm works.and my pwm really works with out any op amp
1. u can see the fan starts to spin 1/2 sec then is starts to spin on 90 % duty cycle
2.u can see the leds blinks like the blinker of cars the it is on 80% duty cycle
P.S:plz plz rate this instructable with higher rating.I'm only 15 years old.Good-bye
my next instructable will be a arc speaker with pwm