February 26, 2015

Know How... 132: Wearable Airbag, PWM Explained, & Feedback

49 minutes

Wearable Airbag, Pulse Width Modulation explained, Smitty shows how to make a clock using meters, Google Plus feedback, and more.

PWM Explained

"Pulse Width Modulation"

It's a way to encode a message into a pulsing signal.

In other words, if you have a signal that can be either on or off (digital), you can modulate the signal to represent more than on and off.

Let's talk about Digital vs. Analog

Take a analog 5-volt circuit: It has an INFINITE number of values between 0 volts and 5 volts. As long as you have equipment that is sensitive to generate and detect EXACTLY how much voltage is being sent, there is no limit to the number of values you can send.

Take a digital 5-volt circuit: It has TWO values -- On and Off -- zero volts and five volts.

It would seem that digital can't approximate analog because of the vast difference in their theoritical values, but it CAN... if you take that circuit and slave it to a clock that switches between on and off at regular intervals.

That's what PWM does!

Take that same 5-volt digital circuit, but now place it behind a clock that cycles once every second.

If the circuit stays off for the full second, that's "0"

If the circuit stays on for the full second, that's "5"

HOWEVER... if the circuit stays on for 1/5 of the second, that's "1"

If the circuit stays on for 3/5 of the second, that's "3"

If the circuit stays on for 1/2 of the second, that's "2.5"

By changing the width of each pulse, we can use a digital signal to approximate an analog one. And in approximating that analog signal, we can send data.

However... it's not just data... we can approximate VOLTAGES by using PWM!

Hosts: Bryan Burnett and Fr. Robert Ballecer, SJ

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