Locations, 2 and 3, are the 16bit unsigned result from the latest ranging - high byte first. The meaning of this

value depends on the command used, and is either the range in inches, or the range in cm or the flight time

in uS. A value of 0 indicates that no objects were detected. Do not initiate a ranging faster than every 65mS

to give the previous burst time to fade away.

Locations, 4 and 5, are the 16bit unsigned minimum range. This is the approximate closest range the sonar

Commands

The are three commands to initiate a ranging (80 to 82), to return the result in inches, centimeters or

microseconds. Another set of three commands (86 to 88) do the same, but without transmitting the burst.

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 and

also a set of commands to change the I2C address.

Ranging

To initiate a ranging, write one of the above commands to the command register and wait the required

amount of time for completion and read the result. The echo buffer is cleared at the start of each ranging.

The ranging lasts up to 66mS, after this the range can be read from locations 2 and 3.

Checking for Completion of Ranging

You do not have to use a timer on your own controller to wait for ranging to finish. You can take advantage

of the fact that the SRF02 will not respond to any I2C activity whilst ranging. Therefore, if you try to read

from the SRF02 (we use the software revision number a location 0) then you will get 255 (0xFF) whilst

ranging. This is because the I2C data line (SDA) is pulled high if nothing is driving it. As soon as the

ranging is complete the SRF02 will again respond to the I2C bus, so just keep reading the register until its

not 255 (0xFF) anymore. You can then read the sonar data. Your controller can take advantage of this to

perform other tasks while the SRF02 is ranging. The SRF02 will always be ready 70mS after initiating the

ranging.

LED

The red LED is used to flash out a code for the I2C address on power-up (see below). It also gives a brief

flash during the "ping" whilst ranging.

Changing the I2C Bus Address

Command

Action

Decimal

Hex

80

0x50

Real Ranging Mode - Result in inches

81

0x51

Real Ranging Mode - Result in centimeters

82

0x52

Real Ranging Mode - Result in micro-seconds

86

0x56

Fake Ranging Mode - Result in inches

87

0x57

Fake Ranging Mode - Result in centimeters

88

0x58

Fake Ranging Mode - Result in micro-seconds

92

0x5C

Transmit an 8 cycle 40khz burst - no ranging takes

place

96

0x60

Force Autotune Restart - same as power-up. You can

ignore this command.

160

0xA0

1st in sequence to change I2C address

165

0xA5

3rd in sequence to change I2C address

170

0xAA

2nd in sequence to change I2C address