Microcontroller basics Embedded systems for mortals

Lesson 3 Serial communication (Devices) I2C communication SPI communication Using a heatsensor

Serial communication Point-to-point communication between two devices Requires two wires minimum (RX and TX) Also recommended to connect the ground wires of the devices together TTL (transistor-transistor-logic) and RS232 voltage levels are different!

Serial communication

Adjustable parameters: Baud rate - Communication speed Data bits - Number of actual data bits in one byte Stop bit - Length of the stop after each sent byte Parity - Used for error checking

Serial communication with Teensy Provides two hardware serial communication methods Serial communication over USB Serial over RX and TX pins (2 & 3) – Works using Serial1 -class in Arduino IDE

Example 8 - Schematic Using hardware serial with Teensy

Example 8 – Breadboard setup Using hardware serial with Teensy

Example 8 - Code byte rxPin = 2; void setup() { pinMode(rxPin, INPUT_PULLUP); Serial.begin(9600); Serial1.begin(9600); } void loop() { if(Serial.available()) //If you recieve data over the USB serial { Serial1.write(Serial.read()); //Send it to hardware serial } if(Serial1.available()) //If you recieve data over hardware serial { Serial.write(Serial1.read()); //Send it to USB serial } Using hardware serial with Teensy

Arduino C – More Serial functions Serial.available() Serial.write() Returns the number of bytes available in the serial input buffer. Write a single byte into the serial port MORE INFO: Serial.read() Read a single byte from the input buffer

I2C communication Bus type communication (one transmits, multiple receives) All the devices in the bus have a specific 7-bit address Requires 2 wires (SDA & SCL) SDA = Serial Data Line SCL = Serial Clock Line

I2C wiring

I2C communication with Teensy Works using the Wire -library in Arduino IDE Not easily understandable library

Example 9 - Schematic Using I2C with Teensy

Example 9 – Breadboard setup Using I2C with Teensy The ADXL345 in the picture is not the one you have! Check the wiring, you have to do your own.

Example 9 - Code #define ADXL345_I2CADD 0x53 #include void setup() { Wire.begin(); //Start up the Wire librarys I2C Serial.begin(9600); } void loop() { //Wire writing Wire.beginTransmission(ADXL345_I2CADD); // starts communication to address (0x53) Wire.write(0x00); // sets register pointer to the command register (0x00) Wire.endTransmission(); //Wire reading Wire.beginTransmission(ADXL345_I2CADD); // starts communication to address (0x53) Wire.requestFrom(ADXL345_I2CADD, 1); // requestFrom(address, quantity) while(Wire.available()) { Serial.println(Wire.receive(), BIN); //show the } Wire.endTransmission(); delay(200); } Using I2C with Teensy

Example 10 1/2 #define ADXL345_I2CADD 0x53 #include byte accelData[2]; //make a vector with a lenght of 2 void setup() { Wire.begin(); Serial.begin(9600); Wire.beginTransmission(ADXL345_I2CADD); //start transmission to device Wire.write(0x2D); // 0x2D is the Power Control register of the ADXL345 Wire.write(0x08); // send value to write (0x08 = 8), so it goes to Measure mode (datasheet) Wire.endTransmission(); //end transmission } Read acceleration value of X-axis with I2C

Example 10 2/2 void loop() { Wire.beginTransmission(ADXL345_I2CADD); Wire.write(0x32); // Go to place in memory where the data acceleration values start, first // two are x-axis. (It needs two bytes for reading 13 bit resolution data) Wire.endTransmission(); Wire.beginTransmission(ADXL345_I2CADD); //begin transmission to 0x53 address Wire.requestFrom(ADXL345_I2CADD, 2); //get two bytes from the adress 0x53 int i = 0; while(Wire.available()) { accelData[i] = Wire.receive(); //write the x-axis acceleration value to the vector i++; } Wire.endTransmission(); i = (int)accelData[1]<<8 | accelData[0]; //left-Bit shifting and bitwise OR two add these //bytes together Serial.println(i); //print the value delay(100); } Read acceleration value of X-axis with I2C

SPI communication Bus type communication The desired recipient is select individually with dedicated wire Requires 2 or 3 wires for the communication +1 wire for each device in the bus Slaves send data to master at the same time when master is sending data to them Our example is the 3 wire spi (MISO, MOSI, SCLK pins) Works using the SPI -library in Arduino IDE

SPI wiring

Example 11: DYI TMP36 Tmp36 is a heatsensor It gives you an analog input signal How can you connect it and read values for it?

Example 11: Wiring

Example 11: Code int sensorPin = 38; //the analog pin the TMP36's Vout (sense) pin is connected to //the resolution is 10 mV / degree centigrade with a //500 mV offset to allow for negative temperatures void setup(){ Serial.begin(9600); //Start the serial connection } void loop() { int reading = analogRead(sensorPin); //getting the voltage reading from the temperature sensor float voltage = reading * 5.0; // converting that reading to voltage voltage /= ; Serial.print(voltage); Serial.println(" volts"); // print out the voltage float temperatureC = (voltage - 0.5) * 100 ; //converting from 10 mv per degree wit 500 mV offset //to degrees ((voltage - 500mV) times 100) Serial.print(temperatureC); Serial.println(" degrees C"); // now print out the temperature (Celsius) delay(1000); //waiting a second }

Feedback Answer to the short survey about the µC exercises Bonus reading: accelerometer-breakout-board.html ADXL345 accelerometer project for Arduino

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