Programming an ATtiny

February 06, 2022

This week I programmed an ATtiny to create a proximity sensor. I used an RCWL-1601 ultrasonic sensor to detect proximity and illuminate an LED based on the distance.

Programming Jig

The programming jig allows me to connect in my Arduino 33 IoT to the ATtiny and upload code using the Arduino as the ISP.

Programming Jig — front

Programming Jig — back

Arduino Code

The program reads from the ultrasonic distance sensor and writes a brightness value to an LED. The output is on pin 0 — one of the two that is capable of pulse width modulation, which allows for a range of values instead of just two.

#define DEBUG 0

const byte DistTrigger = 3;
const byte DistEcho = 4;
const byte LED_PIN = 0;

const int numReadings = 20;

int readings[numReadings];      // the readings from the analog input
int readIndex = 0;              // the index of the current reading
int total = 0;                  // the running total
int average = 0;                // the average

float readDistanceSensor() {
  digitalWrite(DistTrigger, LOW);
  delayMicroseconds(2);
  digitalWrite(DistTrigger, HIGH);
  delayMicroseconds(10);
  digitalWrite(DistTrigger, LOW);
  float duration = pulseIn(DistEcho, HIGH);  // in microseconds
  float distance = duration * 0.0343 / 2.0;  // in centimeters
  return distance;
}

void setup() {
  if (DEBUG) {
    Serial.begin(9600);
    while (!Serial);
  }

  // smooth value by taking average
  for (int thisReading = 0; thisReading < numReadings; thisReading++) {
    readings[thisReading] = 0;
  }

  pinMode(DistTrigger, OUTPUT);
  pinMode(DistEcho, INPUT);
  pinMode(LED_PIN, OUTPUT);
  delay(100);
}

void loop() {
  float distance = readDistanceSensor();

  total = total - readings[readIndex];
  readings[readIndex] = distance;
  total = total + readings[readIndex];
  readIndex = readIndex + 1;

  if (readIndex >= numReadings) {
    readIndex = 0;
  }

  average = total / numReadings;

  int ledBrightness = map(average, 60, 2, 0, 220);
  ledBrightness = constrain(ledBrightness, 0, 255);

  if (DEBUG) {
    Serial.print("Distance: "); Serial.print(distance);
    Serial.println(" cm.");
    Serial.print("Brightness: "); Serial.println(ledBrightness);
  }

  analogWrite(LED_PIN, ledBrightness);
}