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Many times in the world of digital, a device will have to interface with analog components. In our potentiometer tutorial, we used the XBee’s built-in analog-to-digital converter (ADC) to convert the analog voltage values from a pot to digital information that the XBee can transmit. When it comes to outputting analog, the XBee has another trick up its sleeve and it’s called PWM.
PWM stands for pulse-width modulation and it’s a way for digital devices to do their best at acting like they’re outputting an analog signal using a digital to analog converter (DAC). They do this by switching the pin between high and low with different duty cycles. A full 3.3 volts from the XBee will have a 100% duty cycle. That is to say, the PWM output pin will always be high. If you want something half-way between off and on, 1.65 volts, the DAC will keep the pin high for 50% of the time and low for the remaining 50%. This happens very fast—about 16,000 times per second.
XBee radios have two PWM outputs and in this tutorial, we’re going to connect an LED to one of them. When we do that, we can control the brightness of the LED wirelessly.