digital compass with microcontroller

[mahendra.deshmukh]

hi,
we are design the compass using KMZ 51. can you hep us for the compensation coil & flip coil design in KMZ 51. please tell us the total puls required for flipping transistor.
on time & off time for the same.
For compensation coil can you tell us the basic circuit

Thanks & Regards
mahendra deshmukh

 

[FvM]

Did you notice the Philips/NXP application note? www.nxp.com/acrobat_download/applicationnotes/AN00022_COMPASS.pdf

 

[mahendra.deshmukh]

Hi,
Thanks for the reply, i had read the this application note. based on this i had made my schematic.
my problem is in flipping coil & compensation coil circuit design.
as per my understanding the flipping we can do by totem pole ( push pull )method & we can switch the flip coil . i can not understood the time duration for the flip coil switching. please tell that one.

second is the compensation coil. i can note designed the compensation coil design.
please give us basic idea for compensation coil. I have attached the schematic for compensation & flipping coil with micro controller .
please find the attached.

Thanks & Regards
Mahendra Deshmukh

 

[FvM]

I think, the application note answers most of your questions. I don't see the circuit as a totem-pole output. It's rather a bipolar current pulse generator with independent control timing for both drivers. The application note additionally suggests a circuit with active current limiting. But I agree, that there are some unclear points in the AN. The said pulse duration of 3 us can be mainly achieved by the output capacitor, so I wonder, why the driver has a second pulse shaping network in front. You can accept it as an empirical circuit, possibly not exactly dimensioned based on calculations. If your microcontroller is able to generated short pulses in the us range, you may want to think about a software defined timing.

The compensation coil driver requirements can be estimated from the datasheet and intended measurement range, for a compass application about +/- 1-2 mA are required. So an OP current source seems suitable. I guess, you noticed, that the compensated design according to Figure 17 assumes uC D/A converters to drive the two channels. At least, a bipolar drive is required, so your circuit idea can't work.