PWM: Pulse Width Modulation © 2014 Project Lead The Way, Inc.Digital Electronics

2 Imagine 5 LEDs Each with a clock signal of 1Hz. Can you visualize what you would see? Is the frequency different for each LED? What Does a PWM Signal Look Like?

3 Always off. Blinks once/second. On briefly. Blinks once/second. On ½ the time. Blinks once/second. Off briefly Always on. What Does a PWM Signal Look Like?

4 Based on what you have learned: Could you devise a way of making the three blinking LEDS appear to be ON all the time, even though they have different duty cycles? What Does a PWM Signal Look Like?

5 PWM Transmitted by a Microcontroller Pulse Width Modulation is a technique for getting analog results with digital means. Digital control is used to create a square wave. This on-off pattern can simulate voltages in between full on (5 Volts) and off (0 Volts) by changing the portion of the time the signal spends on versus the time that the signal spends off. Theoretically

6 PWM Received by a Microcontroller A microcontroller can compare the time High to the time Total and assign value to that ratio. These comparisons are limited to a range from

Accelerometers 7 The Memsic 2125 is a two-axis accelerometer capable of measuring acceleration up to plus or minus 2g. It has a simple digital interface: two pins (one for each axis) emit pulses whose duration corresponds to the acceleration of that axis. By measuring the length of that pulse, in microseconds, using the Arduino's pulseIn() function, it is possible to determine the rate of acceleration and to use that data for your purposes. Each axis has a 100 Hz PWM (Pulse Width Modulated) duty cycle output in which acceleration is proportional to the ratio tHx/Tx.

Servos 8 VEX 2-wire Motor with motor controller 29 Just as a microcontroller can receive PWM signals, they can produce PWM signals that the motor controller can use to set a speed and direction. VEX Potentiometer with PWM Potentiometer

Servos 9 It the next activity you will explore input and output devices that utilize PWM signals.