Arduino – Bidirectional Serial Communication with Raspberry Pi

You can send data to a Raspberry Pi from an Arduino, have the Pi compute the data and use “intelligence” to send the Arduino a command. This allows you to fully use a Pi as a “Compute Module” for the Arduino with the ability to access databases, data-stores, API’s and anything else a “real” computer can do.

Prerequisites:

Functional Parts in the Project:

Arduino Uno – https://store.arduino.cc/usa/arduino-uno-rev3
560 Piece Jumper Wire Kit – https://amzn.to/2MsCLjL
220 Ohm Resistors – https://amzn.to/2RiiMD9
Breadboard Kit – https://amzn.to/2Xih5ei
LED Kit – https://amzn.to/2Rjhs2N
Analog Temperature Sensor – https://amzn.to/2Rkkl3k
Raspberry Pi
USB Cable

Arduino Sketch

String command;

#define sensorPin A0
#define blueLed 8
#define whiteLed 9
#define redLed 10

void setup() {
  Serial.begin(9600);
  pinMode(blueLed, OUTPUT);
  pinMode(whiteLed, OUTPUT);
  pinMode(redLed, OUTPUT);
}

void loop() {
  int reading = analogRead(sensorPin);
  float voltage = reading * 5.0;
  voltage /= 1024.0;
  float temperatureC = (voltage - 0.5) * 100 ;
  float temperatureF = (temperatureC * 9.0 / 5.0) + 32.0;

  Serial.println(temperatureF); 
  if (Serial.available()) {
    command = Serial.readStringUntil('\n');
    command.trim();
    if (command.equals("white")) {
      digitalWrite(whiteLed, HIGH);
      digitalWrite(blueLed, LOW);
      digitalWrite(redLed, LOW);
    }

    else if (command.equals("blue")) {
      digitalWrite(whiteLed, LOW);
      digitalWrite(blueLed, HIGH);
      digitalWrite(redLed, LOW);
    }
    else if (command.equals("red")) {
      digitalWrite(whiteLed, LOW);
      digitalWrite(blueLed, LOW);
      digitalWrite(redLed, HIGH);
    }
    else if (command.equals("all")) {
      digitalWrite(whiteLed, HIGH);
      digitalWrite(blueLed, HIGH);
      digitalWrite(redLed, HIGH);
    }
    else if (command.equals("off")) {
      digitalWrite(whiteLed, LOW);
      digitalWrite(blueLed, LOW);
      digitalWrite(redLed, LOW);
    }
    else {
      digitalWrite(whiteLed, HIGH);
      digitalWrite(blueLed, HIGH);
      digitalWrite(redLed, HIGH);
    }
    
  }

  delay(1000);
}

Raspberry Python Script

Remember that ttyACM0 may iterate up to ttyACM1

import serial

if __name__ == '__main__':
    ser = serial.Serial('/dev/ttyACM0',9600, timeout=1)
    ser.flush()
    
    while True:
        if ser.in_waiting > 0:
            line = ser.readline().decode('utf-8').rstrip()
            print(line)
            if float(line) <= 60:
                ser.write(b"blue\n")
            elif float(line) > 60 and float(line) <= 70:
                ser.write(b"white\n")
            elif float(line) > 70:
                ser.write(b"red\n")
            else:
                ser.write(b"all\n")