SRF02 Ultrasonic range finder

Technical Specification

Serial Mode

Serial Communication

To use the SRF02 in Serial mode, make sure the Mode pin is connected to 0v Ground.

Serial data is fixed at 9600 baud 1 start, 2 stop and no parity bits. Serial data is a TTL level signal - It is

NOT RS232. Do not connect the SRF02 to an RS232 port - you will destroy the module! If you would like

to connect the SRF02 to your PC's RS232 port, you must use a MAX232 or similar device. It can also be

used (in I2C mode) with the USBI2C module to make a self powered USB ranger, see the examples page for

details. Many small controllers such as the OOPic, Stamp BS2p, PicAxe etc. as well as a wide variety of

micro-controllers have serial ports. To communicate with the SRF02, you simply need to send two bytes,

the address of the SRF02 (factory default is 0) and the command. The default shipped address can be

16 sonar's can be used.

Connections

The connections to the SRF02 are shown below. The "Mode" pin must be connected to 0v ground to place

the SRF02 in serial mode. The Rx pin is data into the SRF02 and should be connected to the Tx pin on your

controller. The Tx pin is data out of the SRF02 and should be connected to the Rx pin on your controller. If

you're using multiple SRF02's, you can connect them all up to the same serial port on your controller.

Connect the Tx from your controller to all the Rx pins on the SRF02's and connect the Rx pin on your

controller to all the Tx pins on the SRF02's. This works because the Tx pins are high impedance (just a weak

pull-up to 5v), except when actually sending data. Just make sure all the SRF02's are programmed to

different addresses.

Commands

To send a command to the SRF02, you need to send two bytes. The first is the SRF02's address 0 to 15,

(0x00 to 0x0F) and then the actual command itself - see below. The are three commands to initiate a ranging

(80 to 82), to produce the result in inches, centimeters or microseconds. These three commands don't Tx the

result back to your controller. You should wait 70mS and then use command 94 to get the result of the

ranging. Another set of three commands (83 to 85) do the same, but also transmits the result of the ranging

back to your controller as soon as it is available. Together, these six commands (80 - 85) are called "Real"

because they perform a complete ranging. There is another set of six commands (86 - 91) called "Fake".

They are the same as the "Real" commands except that they do not send the 8-cycle burst out. These are

used where the burst has been transmitted by another sonar. It is up to you to synchronize the commands to

the two sonar's. There is a command (92) to transmit a burst without doing the ranging.

Command 93 is used to get the firmware revision of the SRF02.

Command 94 gets returns two bytes (high byte first) from the most recent ranging. Put them together to

make a 16-bit result.