Help with 5883L crazyness.

Hi Joey,

This is how I'd try to troubleshoot this - unfortunately I've not used this sensor before, but there is a typical process I would use for sensors:

Basically, try to find known values (e.g. a worked example in the datasheet), and then plug those values into your code so that the data from the sensor

is overwritten with your known values, so you can see if the rest of the coded algorithm behaves as expected. I do it something like this:

#define ALG_TEST 0
... code...
i2c_read(buf); // read into buffer the actual sensor data
if (ALG_TEST)
  {
   buf[0]=0x11;
    buf[2]=0x22;
    buf[3]=0x33;
  }
... data processing ..
... remainder of your code ..

Basically at any point during your code development you can set ALG_TEST to 1 to quickly confirm the algorithm is not broken, and set it back to 0 to go back to normal operation.

The problem is finding some known values and the correct computed value. To do this, perhaps use this arduino compass web page which (about half-way down)

has a screenshot of captured raw values, and the computed results. You could plug the raw values into your code, and check if the result matches.

Another way I frequently use is to come up with some raw values and the expected result by checking if the datasheet has a worked example (in your case unfortunately

the datasheet doesn't have this) or by inventing some sensor values, and writing some formula to generate the output, using (say) Excel.

Then, at any point during testing, I can plug the raw sensor values into the spreadsheet and see what value I expect. This really helps to confirm the coded algorithm is

working well. I do this a lot with virtually any IC. For example, here is my 555 spreadsheet:

I can plug in values into the green cells, and the red cells show the expected output for the 555. I'd suggest a similar thing

with the IC you're using. It takes a while to create, but worth it in the long run.

Also, with the two modules you have, do they both give similar values that match each other?

How are they connected to the RPI - short(ish) wires? What resistors are you using for pull-ups for the I2C -

are these already on the board, or external? Could you attach a photo of the set-up if possible?

Hi Joey,

This is how I'd try to troubleshoot this - unfortunately I've not used this sensor before, but there is a typical process I would use for sensors:

Basically, try to find known values (e.g. a worked example in the datasheet), and then plug those values into your code so that the data from the sensor

is overwritten with your known values, so you can see if the rest of the coded algorithm behaves as expected. I do it something like this:

#define ALG_TEST 0
... code...
i2c_read(buf); // read into buffer the actual sensor data
if (ALG_TEST)
  {
   buf[0]=0x11;
    buf[2]=0x22;
    buf[3]=0x33;
  }
... data processing ..
... remainder of your code ..

Basically at any point during your code development you can set ALG_TEST to 1 to quickly confirm the algorithm is not broken, and set it back to 0 to go back to normal operation.

The problem is finding some known values and the correct computed value. To do this, perhaps use this arduino compass web page which (about half-way down)

has a screenshot of captured raw values, and the computed results. You could plug the raw values into your code, and check if the result matches.

Another way I frequently use is to come up with some raw values and the expected result by checking if the datasheet has a worked example (in your case unfortunately

the datasheet doesn't have this) or by inventing some sensor values, and writing some formula to generate the output, using (say) Excel.

Then, at any point during testing, I can plug the raw sensor values into the spreadsheet and see what value I expect. This really helps to confirm the coded algorithm is

working well. I do this a lot with virtually any IC. For example, here is my 555 spreadsheet:

I can plug in values into the green cells, and the red cells show the expected output for the 555. I'd suggest a similar thing

with the IC you're using. It takes a while to create, but worth it in the long run.

Also, with the two modules you have, do they both give similar values that match each other?

How are they connected to the RPI - short(ish) wires? What resistors are you using for pull-ups for the I2C -

are these already on the board, or external? Could you attach a photo of the set-up if possible?