CMPS10 - Tilt Compensated Compass Module
Serial mode
Connections
|
|
To use the serial mode of operation the mode pin must be connected to ground.
Communication settings
The
Serial mode operates over a link with a default baud rate of 9600 bps (no
parity, 2 stop bits) and 3.3v-5v signal levels.
This is not RS232. Do not connect RS232 to the module, the high RS232 voltages
will irreversibly damage the module.
Commands
Below
is a table describing commands that can be sent to the CMPS10 and the data it
will respond with.
Commands for Serial
|
Command |
Name |
Bytes returned |
Returned data description |
|
0x11 |
GET VERSION | 1 | Software version |
|
0x12 |
GET ANGLE 8 BIT | 1 | Angle as a single byte 0-255 |
|
0x13 |
GET ANGLE 16 BIT | 2 | Angle as two bytes, high byte first 0-3600 |
|
0x14 |
GET PITCH | 1 | Pitch angle +/- 0-85° |
|
0x15 |
GET ROLL | 1 | Roll angle +/- 0-85° |
|
0x21 |
GET MAG RAW | 6 | Raw magnetic data, 16 bit signed: X high, X low, Y high, Y low, Z high, Z low |
| 0x22 | GET ACCEL RAW | 6 | Raw accelerometer data, 16 bit signed: X high, X low, Y high, Y low, Z high, Z low |
|
0x23 |
GET ALL | 4 | angle high, angle low (0-3600), pitch (+/- 0-85), roll (+/- 0-85) |
| 0x31 | CALIBRATE EN1 | 1 | returns ok (0x55) |
| 0x45 | CALIBRATE EN2 | 1 | returns ok (0x55) |
| 0x5A | CALIBRATE EN3 | 1 | returns ok (0x55) |
| 0x5E | CALIBRATE | 1 | returns ok (0x55) |
| 0x6A | RESTORE 1 | 1 | returns ok (0x55) |
| 0x7C | RESTORE 2 | 1 | returns ok (0x55) |
| 0x81 | RESTORE 3 | 1 | returns ok (0x55) |
|
0xA0 |
BAUD 19200 | 1 | returns ok (0x55) |
| 0xA1 | BAUD 38400 | 1 | returns ok (0x55) |
Calibration the CMPS10
I would recommend evaluating the CMPS10 performance first before
implementing this function. Its purpose is to remove offsets caused by constant
magnetic sources around the CMPS10. First of all you need to determine North and
align the CMPS10 with it, then write a sequence of 3 commands in the correct order
with a small delay between bytes, 100ms will be more than adequate. The sequence
to enter calibration mode is 0x31,0x45,0x5A, then calibrate the first point by
sending 0x5E to the command register, this should also light the LED. The Compass should then be rotated 90° and 0x5E
sent to the command register again, repeat for two further 90° rotations and
the calibration completes and the
LED turns off. Please make sure that the CMPS10 is not located
near to ferrous objects as this will distort the magnetic field and induce
errors in the reading.
Restore
of factory calibration
of the CMPS10
To
perform a restore of the factory calibration write a sequence of 3 commands in the correct order
with a small delay between bytes, 100ms will be more than adequate. The sequence
is 0x6A,0x7C,0x81.
Changing
the baud rate
While
the CMPS10 operates at a default serial bus baud rate of 9600 you may wish to
change this. There are two other baud rates that can be used, for 19200 just send 0xA0
or alternatively for 38400 send 0xA1. Please note that the CMPS10 will always default to its
9600kbps rate after power cycling and after setting a new baud rate the ok response (0x55)
will be sent at the
newly selected speed.