Sure compass module

J

John O

Senior Member
Hi All,

I've been following this old thread but it seemed to end without coming to any conclusion.

I've managed to communicate with one of these modules but I can't get much sense out of the returned values. Although the low byte of each axis varies between 0 and 255 (twice in a revolution), the high byte only seems to be either 7 or 8.

It's supposed to be 12 bit resolution but it seems the low 4 bits of the high byte are always either 0111 or 1000, which is really only a 9-bit resolution (ie 2 * 255) or am I missing something?



http://www.sure-electronics.net/download/DC-SS503_Ver1.0_EN.pdf


John.
 
J

John O

Senior Member
I'll be interested if you can get the uart working. I don't think it mentions any signal polarities but it shows it connected to a PC. I tied the "option pin" to 5v to set it to uart operation but couldn't get a peep out of it with a termianl program.

John.
 
A

Andrew Cowan

Senior Member
My module arrived today.

The board has the compass module fitted, then a space where another chip can go. This other chip is a PIC - it is fitted on the serial version of the board.

The pins 'Option, RXD and TXD' are only used if the PIC is fitted - the modules we have are I2C only. Now I just need to work out how to convert an absolute X reading and a Y reading into a bearing - it's going to be pretty hard, I think! I'd imagine you start by working out the relative value (the range), then getting out the triganometry... Fun!

The 7 or 8 you are getting for b1 is fine - these modules give a certain output per gauss (rather than 0-255 as rotated) - you need to make a PICAXE program to calibrate and scale your output.

Andrew
 
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S

sghioto

Senior Member
John,

If it's 12bit don't you need to set I2c address to:

i2c slave %01100000, i2cslow, i2cword

Steve G.
 
J

John O

Senior Member
Andrew Cowan said:
Erm...
(image of 1-chip module)
:confused::confused:
Click to expand...
I've oredered so much stuff recently that I'm not even sure what the postman's going to bring... but, if I remember, this module didn't have a "Buy Now" option so I visited the online shop. It may well be that I ordered the 2-chip module. I looked through their stock last night and both kinds are available.

In the light of what you've siad, I'll have another play with the uart - that seems much easier to interrogate and is supposed to reply with a direct 0 - 360 degree reading.

Edit: Thinking about it, it might well be that some boards have a non-functional second chip so they're still sold as an I2C only board.

John.
 
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J

John O

Senior Member
sghioto said:
John,

If it's 12bit don't you need to set I2c address to:

i2c slave %01100000, i2cslow, i2cword

Steve G.
Click to expand...
IF I'm reading the datasheet correctly, writing a '1' to address 0 will result in 5 x 8-bit bytes being returned as follows:

contents of the internal register
x-axis MSB
x-axis LSB
y-axis MSB
y-axis LSB

As I don't think I need to know what's in the internal register, I've started reading from address 1.

I've just tried 'i2cslave %01100000, i2cslow, i2cword' and changing the read to w0 and w1 but nothing gets returned.

With regard to the axes' MSB, the datasheet says: Even though each axis consists of two bytes, which are 16-bits of data, the actual resolution is limited to 12 bits. Unused MSB should be simply filled by "0"s

What I had expected was for bits 0, 1, 2 and 3 of the MSB to actively count up from 0 to 8 but bits 0, 1 and 2 all change together as bit 4 toggles betwen 1 and 0 (ie 8 and 7).

As Andrew says, there's going to be some sort of mathematical relationship between the x and y axis readings (probably involving sines or something!) but I doubt my maths is up to the task even if the 18M2 is! :)

using the uart would have been a much simpler option -- if I could get it to work - even with two chips on my board!

http://www.sure-electronics.net/download/DC-SS503_Ver1.0_EN.pdf

John.
 
A

Andrew Cowan

Senior Member
OK - it tuns out I have the DC-SS503 (I2C only), while John has the DC-SS504 with the UART. I've ordered myself a PIC16F690 as the hex code for the DC-SS504 is on sure's website - I'll solder it up, program it, and let you know how I get on!

Andrew
 
J

John O

Senior Member
You're a lot more adventurous than me :)

Mine does say SS503 on it so it may be that the part number is printed on after they've tested them?

John.
 
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J

John O

Senior Member
hippy said:
The I2CWORD relates to the addressing size, not the data size, so would likely be I2CBYTE.
Click to expand...
Ah thanks, that would explain why it didn't work :). I'm also trying to remember to use the 'hi2csetup i2cmaster' and 'hi2cin' format so as not to get into the habit of using deprecated commands.

John.
 
A

Andrew Cowan

Senior Member
I guess they only have one type of PCB made (cheaper that way), then either solder on the PIC and sell it as a DC-SS504, or miss out the PIC and sell it as a DC-SS503.

Andrew
 
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A

Andrew Cowan

Senior Member
Right!

My PIC16F690 (microchip sample) has arrived - I've soldered on the PIC, the two missing resisitors and the two missing capacitors. I connected it to my PIC programmer, and downloaded the hex file from sure's website. Now hopefully, I've converted my $5 DC-SS503 into a $15 DC-SS504. Lets see if it works!

A
 
J

John O

Senior Member
Ah, good luck. I'll be interested in how you get on.

Mine's back on the 'pending' shelf at the moment while I work out the best way to use the magentic rotary encoder.

John.
 
A

Andrew Cowan

Senior Member
It works!

For some reason, my Axe027 (reprogrammed to not invert tx and rx) wouldn't work. Sending '$sure su' should return 'unknown command' - instead it was returning 'bad command' for everything. In other words, it wasn't successfully receiving and decoding the $sure part. Any idea why, hippy?

Switching to a different USB-serial adaptor (a CP2102 based model) solved the problem - it now outputs a 0-359 degree serial signal. Fantastic, for £5!

And I soldered the SSOP 208mil package without any problems - very satisfying!
 

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B

BillyGreen1973

Senior Member
Andrew, am I right in thinking the compas module is linked direct to your PC and not via a Picaxe?

If so, what strings have you sent to the module from your terminal program?

Thanks
 
A

Andrew Cowan

Senior Member
You can see the terminal window in the top corner of my attachement (post 17).

$sure ga returns the angle of the sensor, $sure cl to calibrate, and $sure sv=-2 to set my magnetic declination.

Note the module uses true polarity TTL data (unlike the axe027 which uses inverted TTL, and a standard serial port, which uses true RS232 data).

Andrew
 
B

BillyGreen1973

Senior Member
Andrew Cowan said:
Note the module uses true polarity TTL data (unlike the axe027 which uses inverted TTL, and a standard serial port, which uses true RS232 data).
Click to expand...
So you are using a CP2102 (or similar) to do convert from TTL serial to USB, and not connected via a picaxe?
I see now, thought you were using a picaxe to do the conversion and using the programming cable as the link to your terminal.
 
A

Andrew Cowan

Senior Member
You're right, although it would be a very simple task now to connect a PICAXE to it - using serout, then serin, then sertxd. The code is very simple - something like:

Code: 
do
serout T9600 ("$sure ga",13,10)
serin T9600 ("="),#b0
sertxd (#b0,13,10)
pause 500
loop
 
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