Stimulus Voltage
As shown in a previous section, the electrodes need a ramp of voltage in order to activate the
arsenic in the water. The MSP does not have an onboard digital-to-analog converter (DAC), so a
software DAC was assembled to facilitate our need. The MSP provides a pulse of varying duty cycles
(percentage of wave that is logic high) to the circuit. This pulse signal is filtered for the average DC
value of the pulse. The duty cycle starts low at first, gradually increasing until the DC value is 3.3
V (a duty cycle of 100%). It is this pulse that needs to be tested.