Pulse Width Modulation (PWM) is a technique widely used in electronic circuits to control power delivery to devices. By modulating the width of the pulses in a signal, PWM allows for precise control over the amount of power delivered to a load, such as an LED. This experiment demonstrates the construction of an analog PWM modulator using a sawtooth waveform and a reference voltage to control an LED's brightness.
Objective
The objective is to build an analog PWM modulator using the Red Pitaya's function generator to create a sawtooth waveform for the comparator's inverting input, with a DC voltage serving as the reference at the noninverting input. This setup aims to explore the modulation of an LED's brightness through PWM and experiment with varying the reference voltage characteristics.
Materials and Setup
- Red Pitaya or equivalent function generator and oscilloscope
- Comparator (OPAmp or similar)
- LED
- Potentiometer or second output channel of Red Pitaya for reference voltage
- Resistor for LED current limiting
Circuit Assembly
- PWM Modulator Configuration: Arrange the comparator in a circuit where the sawtooth waveform from the Red Pitaya feeds into the comparator's inverting input, and a DC voltage from another channel or a potentiometer provides the reference voltage at the noninverting input.
- LED Connection: Incorporate an LED, with an appropriate current-limiting resistor, to the output of the comparator to visualize the PWM modulation effects.
Conducting the Experiment
- PWM Modulation: Activate the Red Pitaya's function generator to produce a sawtooth waveform and a DC reference voltage. Observe the modulation effect on the LED's brightness as the comparator's output varies based on the input sawtooth and reference voltage.
- Reference Voltage Variation: Experiment with changing the DC reference voltage to a sine wave, adjusting its amplitude to be less than the sawtooth to ensure proper modulation without clipping.
Analysis and Observations
- Brightness Control: The comparator outputs a PWM signal controlling the LED's brightness, with the duty cycle adjusted by the relative voltages of the sawtooth and the reference.
- Effect of Reference Voltage Type: Using a DC voltage as the reference simplifies observing the PWM's impact on LED brightness. Switching the reference to a sine wave introduces a dynamic change in the PWM signal's duty cycle, illustrating how different waveform types can modulate the PWM output.
Conclusion
This experiment showcases the versatility of PWM modulation for controlling devices like LEDs, utilizing a simple analog comparator setup. By employing a sawtooth waveform and varying the reference voltage, we've demonstrated how to achieve adjustable brightness control over an LED. Further exploration with different reference waveforms, such as sine waves, highlights the potential for more complex modulation schemes, underscoring the importance of carrier frequency selection relative to the signal's frequency for achieving desired modulation effects. This foundational understanding opens avenues for further experimentation with PWM in various applications, from lighting control to signal processing.