I thought I might experiment with a solid state compass chip.
Jaycar conveniently has a Arduino Compatible 3 Axis Compass Magnetometer Module
https://www.jaycar.com.au/arduino-compatible-3-axis-compass-magnetometer-module/p/XC4496
So I ducked in and bought one. $17.95
PROBLEMS
1. Board Supplied is not board pictured.
2. No information on whether the I2C is 3V or 5V (Now determined as 5V)
3. Data sheet is not a data sheet. More of a 'glossy'
31-3-2021 1pm update.
The supplied board does not have a genuine Honeywell chip.
The Honeywell I2C read address is $3D and write at $3C.
This chip responds at $60 & $61 ($=Hex)
This is the web page.
This is the data sheet. The entire data sheet.
This is the actual board supplied.
The magnetic sensor might be a Honeywell HMC5883L. The Honeywell datasheet tells me it's a 3V part. Not Honeywell chip though.
https://cdn-shop.adafruit.com/datasheets/HMC5883L_3-Axis_Digital_Compass_IC.pdf
I am hopeful the the chip marked 702 is a level translator for the I2C but with no schematic and no data sheet and no idea what the 702 actually is there is a bit of a risk
YES 5V I/O. Not Honeywell chip though.
This is a partial schematic of the supplied board.
I powered it up and confirmed that the SDA and SCL lines are pulled up to 5V.
This makes it easy to connect to a 5V microprocessor.
SOFTWARE
I2CScan shows this device has an address at Hex60
So obviously not a Honeywell chip which according to the data sheet is at Hex3C
When I read the registers from it, I get
00 00 00 00 00 00 00 10 10 10 10 10
Never changes => Either
a dud chip which I doubt.
I am sending the wrong command. <- Possibly because I have no data
I2C Inexperience.
' I2creceive slave, var, b2W, b2R
' | | | |
' Address | | Number of Bytes to receive
' | Number of Bytes to Write
' Receive variable
memfill Buffer(1) , 12 , &HFF ' So we can see if it changes
Buffer(1) = 00
I2creceive &H60 , Buffer(1) , 1 , 12
' addr=60 00
Print "II2creceive Error : " ; Err
For B = 1 To 12
Print Hex(Buffer(B));" ";
Next
Print
I have been having trouble reading from the compass chip.
The reason could be that my program simply does not read anything. So I got a PCF8574 I2C port extender. Must be the simplest I2C device in existance and has been around since the '80's
Wired it up and it works
if ks = "TR" then
' Read from PCF8574T
' Address is $7E
memfill Buffer(1) , 12 , &HFF
'Buffer(1) = 00
I2creceive &H7E , Buffer(1) , 0 , 2
' addr=60 00
Print "II2creceive Error : " ; Err
For B = 1 To 2
Print Hex(Buffer(B));" ";
Next
Print
End If
if ks = "TW" then
' Write to PCF8574T
' Command is
' TW 6A
' \
' Hex of what to write
' Address is $7E
' 76543210 76543210
' 10101010 10001010
' A A 8 A
Temp_str = Get_token( Command_str, 2)
Temp_b = HexVAL(Temp_str)
memfill Buffer(1) , 12 , &HFF
'Buffer(1) = 00
Buffer(1) = Temp_b
I2CSEND &H7E , Buffer(1) , 1
Print "I2CSEND 8574 ";hex(Temp_b);" Error : " ; Err
End If
So at the moment we have both devices on the same bus.
The 8574 works.
Conclusion
1. The Basic program can read and write I2C
