Note: The time scale has been reduced in half to show more detail of the signal Change the on time to 1 and the off time to 4. And we don’t have much more room to move as we only have the values 1-4 to adjust for on or off time.Īnd here’s the good news… “since the light is only on 50% of the time, we are saving 50% in electricity costs!”. Note that we haven’t changed the width of the pulse, only the number of pulses per second or frequency. It is now blinking 100 times per second which is faster than the human eye can discern. Now I don’t believe you are able to see the LED flicker. Does the LED flicker? Maybe a little, or doesn’t seem sharp? The positive duty cycle (typically referred to as duty cycle) is the % of time the wave is high, in this case, 15ms of the 30ms or 50%.The frequency is the reciprocal of the period or 33Hz, meaning a full cycle happens 33 times per second or 33Hz.The period is the length of time it takes for a full cycle, in this case 30 ms.Note the time scale at the bottom of the image, and the voltage on the left hand side. Note: The image is from an oscilloscope, it shows the voltage on the LED over time. Try it with your blink program, set the on time to 15 and the off time to 15 and are you able to see it blink or flicker? ( Its best to try this on an LED plugged into the breadboard, not the on-board LED.) blink using 15ms on and 15ms off If the combined time on/off is greater than 20ms (or 20/1000 second), chances are we will see flickering as the human eye can discern a frequency of down to about 60Hz or 1/60 or 16/1000 second. We turn the LED on for a period of time, then we turn it off. As a light’s blinking increases in frequency, the eye begins to see it as a constantly lit bulb.įor example, think about our blink program. Understanding what the eye can seeįirst, let’s understand the impact of frequency on visibility. While there are a lot of applications for PWM, the easiest one to immediately understand is using PWM to reduce the energy used by a LED. Changing the width of a square wave or pulse over time, is called modulation, hence the term, pulse width modulation or PWM.This video is showing a sqare wave that is expanding and contracting on the screen.
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