I’m looking for an AHRS sensor with true Heading: I saw the TM200 but I’m not sure about the true Heading (0 on the North)
Hello @snicolas !
Welcome to the forum! Yes, the TM200 is the only sensor available in the store. Looking into the datasheet I found what I think you are looking for:
The TransducerM calculates the Yaw (heading) angle based on the magnetometer reading during its initialization processshortly after its power on. That is, the local magnetic field during the TransducerM start up is recognized as the referencemagnetic field, and if the X-Axis of TransducerM (the sensor frame) is pointing to the north direction of this local magneticfield, the Yaw (heading) reading is zero degree.
Hope this could help you ! 
So, I have no calibration to perform to have yaw=0 when x axis is pointing to the north ?
does the TransducerM provide ASCII message or NMEA message through the serial line ?
Thank you
Stéphane