Open Lab2 in the Arduino IDE. Save As Lab3. Here is a template for your to be written sensorRead() function.

uint8_t sensorRead(uint8_t sensor_pin, uint8_t current_level) {
  1. read analog value 
  2. conditional expressions set return logic_level based on analog value read and trigger points.
  3. if the analog value is in the undefined region (no mans land) then logic_level equals the current_level argument.  
  return logic_level; // return HIGH or LOW 
}

The sensorRead function returns HIGH if the analog value is greater than or equal to trigger1, and LOW if the analog value is less than or equal to trigger0. When the analogRead() function returns any value that is neither (gray area), your function should return the current logic level (HIGH or LOW).  This is known as hysteresis and will keep your robot from reacting too quickly to changes in the input (noise). To implement hysteresis, your function receives as its’ second argument (current_level) the last returned value.

To determine my trigger points I followed these steps.

1. hysteresis = (high value – low value)/2
2. trigger1 = high value  – hysteresis/2
3. trigger0 = high value + hysteresis/2

For my IR sensors when over black the recorded digital numbers were very volatile but usually over 300. When over white the recorded value was fairly stable at 79. Although, if I simulated going over a bumpy surface this value could spike up wildly. So a hysterics value of  221 DN seemed like a reasonable number with trigger1, therefore, set to  245 and trigger0 set to 135. Based on your experiments, you may want to implement a different set of criteria for setting your trigger points and possibly even use the runningAverage script found in the StatPak tab to remove high-frequency noise from your sensor readings. Open the 3DoTConfig.h tab and set the trigger points where an analog reading; a digital number (DN) between 0 and 1023 is translated to a digital HIGH or LOW value

/* IR sensor constants */ 
const uint16_t trigger1 = ____;   // IR values 1023 to ____ = 1 (black) 
const uint16_t trigger0 = ____;   // IR values ____ to  0 = 0 (white)

Return to the home tab.  If you have not done so already, complete writing the sensorRead() function.

To maintain compatability with the Arduino digitalRead() function, your sensorRead() function will return a data type uint8_t with values HIGH or LOW. If you are converting your Arduino script to a C program,  then I would recommend switching to a bool datatype, with a value of true or false.

Now that you have identified your trigger points and written the sensorRead() function, you are ready to update the “Read the IR sensors” block within takeAStep to improve your robot’s ability to follow the path.

In takeAStep() within the “Read the IR sensors” block, replace the digitalRead() Arduino functions with your new sensorRead() function.  Add this new function at the end of takeAStep().  Your program should now look something like this. Observe that sensorLeft and sensorRight are both arguments sent to and returned from sensorRead. Therefore, they must be defined as static uint8_t data types before the call to sensorRead. The subject of the next section.

void loop() {
  takeAStep();
}

void takeAStep(){
  /* Read the IR sensors (lab 3) */
  uint8_t sensorLeft = LOW; // initial value white, motor ON
  uint8_t sensorRight = LOW;
  sensorLeft = sensorRead(IR_L_I,sensorLeft);   // White = 0, LOW
  sensorRight = sensorRead(IR_R_I,sensorRight); // Black = 1, HIGH
  /* Run the path following algorithm */
  Remainder of path follower code from Lab 2
}