D/A Conversion Using PWM and R-2R Ladders to Generate Sine and DTMF Waveforms AN655. AN655 DS00655A-page 2. The tone generator can play four different waveforms: Sine, Square, Sawtooth and Triangle. Click on the buttons to select which waveform you would like to.

Pulse Width Modulation ( PWM) is a technique in which the width of a pulse is modulated keeping the time period of the wave constant. The ON time and OFF time can have any different values in the wave cycles, but the sum of the ON time and OFF time remains same for the entire cycles. PWM is a digital wavethat can be generated using digital circuits which are not capable of generating analog voltages. With the help of the modulation of the width of a pulse in a period of the wave, they can generate any required voltage with the help of a proper filter circuits.

The filter circuits are used for generating the voltage corresponding to a modulated wave. Hence the PWM wave is always associated with a filter circuit. This feature of the PWM wave is making use in so many digital systems like DC motor control, audio devices, simple decoration light controls etc. The has an inbuilt PWM module which can generate continuous PWM waves. This project explores the PWM module of the PIC18F4550 and tries generating a sine wave with the help of a filter circuit.

Generating a sine wave has a great deal of importance since the sine wave is the most natural waveform and all other kind of waves can be generated as a combination of sine waves with different frequencies and amplitude. Bhai 2013 telugu movie torrent download full. The PIC18F4550 has four PWM output channels and they are P1A, P1B, P1C and P1D.

All of them are capable of generating PWM waves at a time. In this project only one of the PWM channels are using.

The P1A is the PWM channel in this particular project. A simple example of the of waves generated at this pin is shown below; As shown in the above figure the ‘Period’ of all the wave remains the same but their ‘Duty-cycle’ varies. The period of the wave is the sum of the ‘ON time + OFF time’. Duty-cycle is the percentage of time period for which the logic1 voltage exists in a cycle (ON time), starting from the beginning of the cycle. The PWM is that kind of a wave in which the ON time and OFF time can vary in a cycle but the sum of ‘ON time + OFF time’ remains constant for every cycle. The period and the duty cycle for a PWM wave can be calculated generally using the following equations; Period = ON time + OFF time Duty-cycle = ON time / (ON time + OFF time) = ON time / Period As shown in the figure, the first PWM wave has a Duty-cycle of 50% which means the on-time is exactly half of that the period of the wave. The second wave has 10% Duty-cycle and the third wave has 90% Duty-cycle.

According to the modulation of the width of a pulse in a period of the wave, the PWM can generate any required voltage with the help of a proper filter circuits. The filter circuits are used for generating the voltage corresponding to a modulated wave. Hence the PWM wave is always associated with a filter circuit.

When applied to a proper filter the 50% duty cycle can produce half of the maximum voltage of the pulse. If the maximum voltage (logic 1 voltage) of the pulse is 5V then the 50% duty cycle wave can produce a continuous 2.5V. The 10% duty cycle wave can produce nearly 0 voltages and the 90% duty cycle wave can produce nearly 5V.Thus the wave when applied to a filter can continuously produce a voltage which is the average of the voltage in a single period. Increasing the Duty-cycle will increase the voltage at the filter device’s output and decreasing the Duty-cycle will decrease the voltage as well The filter could be any device which can generate the equivalent voltage of a PWM wave.

It normally consists of, amplifiers, load drivers etc. They generate the voltage corresponding to the pulse width modulation in the wave and can fed that voltage to the load device. The associated with the PWM modules like CPR1, PR2 and TMR2 etc. Can be used to set the required Period and Duty-cycle in a PWM wave. The voltage generated by the PWM wave at a filter device can vary by simply varying the Duty-cycle of the PWM wave. Increasing the Duty-cycle will increase the voltage at the filter device’s output and decreasing the Duty-cycle will decrease the voltage as well.

In this particular project the sine wave samples are generated periodically by re-writing the value of the CCPR1 register to vary the Duty-cycle. It is done by generating interrupts periodically with another timer module and changing the CCPR1 value when the code is inside the timer0’s ISR. It is done as shown in the following figure; The voltage generated by the PWM wave in the interval between two interrupts will be a constant value and this time period can be called ‘sampling period’. The values of voltage that appears at each sampling period are simply called ‘samples’. A sampling time can have 10 to 500 PWM cycles normally and depends on the particular output device requirement. Hindi style font free download. The more the number of PWM cycles in a Sampling time, more stable the output voltage will be The Duty-cycle of the PWM wave is increased in a sinusoidal way each times the timer0 fires and to perform such a thing one has to configure the properly. The consecutive samples that should be generated at each sampling time should follow a sinusoidal pattern.