Pulse Width Modulation (PWM) is a technique widely used in electronics for controlling power to inert devices. By adjusting the PWM signal's duty cycle, it's possible to control the brightness of LEDs effectively, taking advantage of the human eye's limited "framerate" to create the illusion of varying brightness levels.
Objective
This experiment aims to demonstrate the effect of PWM on LED brightness control, using the Red Pitaya's built-in PWM generator. We'll explore how changes in PWM settings affect LED brightness and investigate the relationship between PWM frequency, duty cycle, and the perception of continuous light versus flickering.
Materials and Setup
- Red Pitaya or equivalent device capable of generating PWM signals
- LED
- 100 Ohm resistor (for series connection with the LED)
- Wires and breadboard for circuit assembly
Circuit Assembly
- PWM Signal Connection: Set the Red Pitaya to output a PWM signal at full amplitude on Output 1. Connect this output to an LED in series with a 100 Ohm resistor.
- Grounding Technique: To eliminate the need for signal amplification, set the second output channel to output a DC voltage at 0V with an offset of -1V. Use this as the ground connection for the LED circuit.
Conducting the Experiment
- Brightness Control via PWM: Adjust the PWM settings (duty cycle and frequency) on the Red Pitaya and observe changes in the LED's brightness. Experiment with different frequencies to find the threshold at which the LED's flickering becomes perceptible to the human eye.
- Exploring Human Perception: Set the PWM duty cycle to 50% and the modulation frequency to 30 Hz. Observe the LED to determine whether blinking is noticeable, testing the myth regarding human visual perception limits.
- Motion Test: Move the LED rapidly while it's being modulated by the PWM signal to observe discrete spots along its trajectory, indicating the presence of PWM modulation.
Analysis and Observations
- PWM Frequency and Human Perception: At high PWM frequencies, the LED appears to emit a constant light, while at lower frequencies, flickering becomes noticeable, demonstrating the PWM's impact on perceived brightness and the limitations of human vision.
- Peripheral Vision Sensitivity: Testing the sensitivity of peripheral vision to pulsating light can reveal differences in how flickering is perceived at the center versus the edges of the visual field.
Conclusion
This experiment with PWM-controlled LED brightness not only demonstrates practical applications of PWM in electronics but also offers insights into human visual perception. By adjusting PWM settings, we can observe how LEDs can be dimmed effectively without a linear change in power supplied. The exploration of flickering at lower frequencies versus the illusion of continuous light at higher frequencies underscores the importance of PWM frequency selection in applications sensitive to flicker, such as LED lighting and display technologies. Additionally, the experiment invites curiosity about the intricacies of human perception, challenging preconceived notions about what we can and cannot see.