CS 353 Fall 2020     Syllabus       Labs/Projects

Goals

• Design a circuit based on component specifications.
• Wire components based on self-drafted circuit design.
• Use a timer to calculate the amplitude of a signal over a window.
• Have an RGB LED smoothly transition between 5 different colors.

Design Your Circuit

RGB LED - Common Cathode

• Equations:
  • V_resistor = I_resistor * R_resistor
  • V_power = V_LED + V_resistor
• Figure out which pins of the Arduino you can use analogWrite() with.
  Do not use Pins 9 and 10 because we will be using timer1 for the microphone.

Wire the Microphone

Find Microphone Min and Max values over a 128ms Window

• Using the ATmega datasheet, with registers setup timer 1 as a CTC timer with a prescalar of 64.
• With registers, enable the timer compare interrupt.
• Set the compare match register (ORC1A) to [ Arduino clock speed / (prescaler * desired interrupt frequency) ] - 1.
  • The Arduino clock speed is 16 megahertz.
  • Call the interrupt every 1ms.
  • 1 second is equal to 1 hertz frequency.
• ISR(TIMER1_COMPA_vect){}, will be called every 1 millisecond. We want to find the minimum and maximum microphone readings over a 128 millisecond window. Ignore any spurious readings >= 1024. When the 128ms window is complete, calculate the peakToPeak (maximum-minimum), and reset the maximum, minimum and count.
• Test the system, by printing peakToPeak in the loop to the serial port and see how it responds to different volume levels.

Wire the RGB LED

Program the circuit

• 0 should be Blue. RGB = (0, 0, 255).
• 256 should be Green. RGB = (0, 255, 0).
• 512 should be Yellow. RGB = (255, 128, 0).
• 768 should be Red. RGB = (255, 0, 0).
• 1024 should be Purple. RGB = (128, 0, 128).