//Frequency and amplitude sweep tool for testing frequency and/or amplitude sensitive devices //Output is square wave frequency sweep at specified output level (peak-peak % of full-scale DAC output), //or p-p amplitude sweep at specified frequency. The output appears on Teensy pin A21 (DAC0). //the output square wave is echoed to Teensy digital output pin 33 for frequency monitoring //Teensy digital output pin 1 is toggled HIGH at the start, and LOW at the end of each sweep //Measurement input is expected on analog input pin A12. This pin is read once at the end of each sweep step