This lab has the student build an improved DAC that uses fewer I/O pins and provides greater precision than the DAC built around the R2R ladder network. These improvements are obtained by thinking of using "time" as a control variable.
The MicroStamp11 is a digital device and it is because of its digital nature that we needed so many I/O pins in the earlier DAC design. Micro-controllers, however, can do more than manipulate digital data. Micro-controller must have internal clocks that precisely orchestrate the various digital computations performed by the device. In other words, the micro-controller can detect and generate timed events with a great deal of precision. This is precisely what you took advantage of in the preceding lab when you used the MicroStamp11 to generate a pulse width modulated (PWM) signal.
In this lab you will build a DAC that uses the PWM signal you generated in the previous lab to drive a simple circuit consisting of a capacitor and resistor. This circuit is called an RC circuit. The RC circuit's response to the PWM input signal is a time-varying signal whose average value is proportional to the duty cycle of the PWM signal. You should be studying capacitive circuits in your lecture course right now.