Challenge: STEMTera Digital Inputs and Encoders

Updated 9/28/2020
ECE 206: STEMTera and Encoder
Challenge: STEMTera Digital Inputs and Encoders
In this lab, we’ll follow up your work on Lab 2. Our goal is to design a circuit as well as the associated
software to read and keep track of the position of the encoder using a STEMTera.
Prelab Deliverables: (due at the end of class on Compass)
• Consider your scope traces from Lab 2. How many times/second would you need to read the
value of the A and B signals to keep track of the encoder position in the “slow” case? How many
times/second in the “fast” case? Explain your answer based on what you recorded in your
scope traces. (Note: You can assume each time index in Serial Plotter equals x seconds and leave
your answers in terms of x.)
Challenge:
• Rebuild or otherwise construct the circuit you used in Lab 2 to read the A and B channels of the
encoder into the STEMTera. Connect A and B channels to some STEMTera pins. Use an
additional 7 pins to control the 7 segment LED (you won’t need the decimal point) to display
digits 0-9.
• Use the encoder to increment and decrement the digit based on knob rotation. Clockwise
rotation should INCREASE the number shown (up to 9), and counter-clockwise rotation should
DECREASE the number shown (down to 0). Demonstrate your working circuit to your TA.
Bonus Challenge: Use the second digit of the LED to make your circuit work between 0 and 99.
Hints: You should have created a flowchart after Lab 2 which can be used to decode A and B signals from
the encoder to a count. The skeleton code for your design is provided as follows:
Updated 9/28/2020
int total_rotation = 0; //this is a global variable all functions can access
int last_a = 0;
// one time run setup function
void setup() {
// initialize digital pins 12/13 to be inputs (channels A and B respectively)
 pinMode(12, INPUT);
 pinMode(13, INPUT);
}
// infinite loop for real-time operation
void loop() {
 int a = digitalRead(12);//read pin 12, call it 'a'
 int b = digitalRead(13);//read pin 13, call it 'b'
if ((last_a == LOW) && (a == HIGH)){
 //if A has gone from low to high
 //you should do something here depending on B
}
if ((last_a == HIGH) && (a == LOW)){
 //if A has gone from high to low
 //you should do something here depending on B
}
//display the new value here on the LED
 last_a = a; //update last_a
}
When plotted on a state diagram, the strategy of the code above looks something like the diagram
below. (Note that clockwise/counterclockwise may be reversed in this diagram):
Updated 9/28/2020
Report Deliverables:
• Include a diagram/sketch of you circuit.
• Include commented code for your design.
• Obtain your TA signoff on the circuit in operation
• Bonus challenge: relevant diagrams, sketches, code and explanations (Bonuses are optional)
Report should contain, at minimum the following elements:
• Title, Names, Dates
• Statement of Purpose
• Plan and Execution
• Results / Conclusion
o Answer any questions posed in the lab challenge.
o Explain your understanding of what happened and why.