Interfacing SRF02 with Pluguino v2

Interfacing SRF02 with Pluguino v2

1024 576 Yaniv

The SRF02 is a single transducer ultrasonic rangefinder in a small footprint PCB. It features both I2C and a Serial interfaces. The serial interface is a standard TTL level UART format at 9600 baud,1 start, 2 stop and no parity bits, and may be connected directly to the serial ports on any microcontroller.

Up to 16 SRF02’s may be connected together on a single bus, either I2C or Serial. New commands in the SRF02 include the ability to send an ultrasonic burst on its own without a reception cycle, and the ability to perform a reception cycle without the preceding burst. This has been as requested feature on our sonar’s and the SRF02 is the first to see its implementation. Because the SRF02 uses a single transducer for both transmission and reception, the minimum range is higher than our other dual transducer rangers. The minimum measurement range varies from around 17-18cm (7 inches) on a warm day down to around 15-16cm (6 inches) on a cool day.

Connection

  • SRF02 is an I2C and UART Compatible device
  • V and G goes to the Vcc and GND pins of SRF02
  • Mode Pin leave free for I2C operation
  • Mode Pin connect to Ground for the UART operation.

Code:

#include <Wire.h>

void setup()
{
  Wire.begin();                // join i2c bus (address optional for master)
  Serial.begin(9600);          // start serial communication at 9600bps
}

int reading = 0;

void loop()
{
  // step 1: instruct sensor to read echoes
  Wire.beginTransmission(112); // transmit to device #112 (0x70)
  // the address specified in the datasheet is 224 (0xE0)
  // but i2c adressing uses the high 7 bits so it's 112
  Wire.write(byte(0x00));      // sets register pointer to the command register (0x00)
  Wire.write(byte(0x51));      // command sensor to measure in "centimeters" (0x51)
  // use 0x51 for centimeters
  // use 0x52 for ping microseconds
  Wire.endTransmission();      // stop transmitting

  // step 2: wait for readings to happen
  delay(70);                   // datasheet suggests at least 65 milliseconds

  // step 3: instruct sensor to return a particular echo reading
  Wire.beginTransmission(112); // transmit to device #112
  Wire.write(byte(0x02));      // sets register pointer to echo #1 register (0x02)
  Wire.endTransmission();      // stop transmitting

  // step 4: request reading from sensor
  Wire.requestFrom(112, 2);    // request 2 bytes from slave device #112

  // step 5: receive reading from sensor
  if (2 <= Wire.available())   // if two bytes were received
  {
    reading = Wire.read();  // receive high byte (overwrites previous reading)
    reading = reading << 8;    // shift high byte to be high 8 bits
    reading |= Wire.read(); // receive low byte as lower 8 bits
    Serial.print(reading);   // print the reading
    Serial.println("cm");
  }

  delay(250);                  // wait a bit since people have to read the output 🙂
}

 

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