Project:HM55B
About the module
$20-25 compass module for embedded systems, this comes in a convenient DIL package.
The SMD will probably be cheaper, though I have not managed to source one yet.
Bus Pirate pinout
From http://dangerousprototypes.com/docs/Bus_Pirate_101_tutorial
Pin name Description (Bus Pirate is the master) MOSI Master data out, slave in (SPI, JTAG), Serial data (1-Wire, I2C, KB), TX* (UART) CLK Clock signal (I2C, SPI, JTAG, KB) MISO Master data in, slave out (SPI, JTAG) RX (UART) CS* Chip select (SPI), TMS (JTAG) AUX Auxiliary IO, frequency probe, pulse-width modulator ADC Voltage measurement probe (max 6volts) Vpu Voltage input for on-board pull-up resistors (0-5volts). +3.3v +3.3volt switchable power supply +5.0v +5volt switchable power supply GND Ground, connect to ground of test circuit
In the photo the pins on right connector, from top left:
GND +3.3V +5V ADC Vpu AUX CLK MOSI CS MISO
Connecting
Wiring
HM55B Bus Pirate Din(1) MOSI Dout(2) MISO VSS(3) GND CLK(4) CLK /EN(5) CS Vdd(6) +5V
Starting a terminal session
Plug in the bus pirate then (assuming it's the only USB device plugged in a debian based os):
$ screen /dev/ttyUSB0 115200
Testing with the BusPirate
Once in the terminal session, apply these settings:
- M (mode)
- 8 (3-wire raw)
- 4 (400KHz)
- 2 (3.3V high)
- W (turn on 5V output)
Checkpoint
There should now be +5v measured between HM55B pins 3 and 6.
Reset
\[/_\/_\/_\/_\&:10]
The delay may not be needed.
Take sample
1100 is the response for success, 00xx is for incomplete, xx11 is error, see p9 of datasheet)
\[/-\/_\/_\/_\&&]&:10[&:10/-\/-\/_\/_\!!!!&!!!!!!!!!!!&!!!!!!!!!!!]
READ BIT: 1 READ BIT: 1 READ BIT: 0 READ BIT: 0 DELAY 0b00000001uS READ BIT: 0 READ BIT: 0 READ BIT: 0 READ BIT: 0 READ BIT: 0 READ BIT: 0 READ BIT: 1 READ BIT: 0 READ BIT: 0 READ BIT: 0 READ BIT: 0 DELAY 0b00000001uS READ BIT: 1 READ BIT: 1 READ BIT: 1 READ BIT: 1 READ BIT: 1 READ BIT: 1 READ BIT: 1 READ BIT: 1 READ BIT: 1 READ BIT: 0 READ BIT: 0
Note that &:50000 isn't enough of a delay, but && works, presumably because BusPirate parser adds a huge delay. This means that we don't know how fast this module can be clocked, because each ! will be > 50ms apart.
The BusPirate wiki suggests this will work (since we've determined that it still provides the 22 sample bits even if the reading is incomplete):
\[0b0000 &] [0b1000 && ]&[& 0b1100 r:4]
Sample readings:
0,-6
-1,-11
-1,-19
Exiting
ctrl-a \y
