Initial feedback and troubleshooting guides on the forum and wiki suggested that interference could be causing spikes on the sonars test (LV and MB1200) versions which in turn provided rough output to the APM.
Scoping the power supply lines, the suggestion to add a resister and capitor certainly cleaned up the power supply noise but produced an additional disturbance due to the momentary high current draw of the outgoing sonar pulses. The additional disturbance of 200mv was within the specifications for the board and did not seem to contribute to any disturabances from the outgoing analogue signal.
Other possible disturbances could be:
- Ultrasonic noise from the propellor blades
- Ultrasonic nosie from the motors'
In order to cancel our this possibilities, we tested the unit in a workshop:
- Props removed
- Motors not running
In both cases there was still erratic analogue signal as displayed on our scope and checking the graph data on APM Mission Planner.
We then decided to remove the sonar all together from the quadcopter and connected it to a stabilzied bench power supply. The signal lines were then monitored only using an oscilliscope.
Again erratic random behaviour of the analog signal line was noted.
Scoping various parts of the sonar circuit, the received relections could be seen and the input to the PIC in pin17 well seen. There was however considerable clutter and in my opionion, the PIC programing more than likely requires refining in order to properly solve the required signal from the clutter.
In conclusion, it is possible that the test units LV and MB are in some way defective or have outdated PIC software, however what is clear is that it is possible to demonstrate the eratic behaviour when completely seperated from the aircraft. In addition to this, none of the erratic behaviour changed by engaging the motors, with or without props attached.
Regards,
Solo.
Replies
James,
To you have any pictures or screen shots of the set-up you used or the size of the disturbances? It would be nice to see some idea of the size of the spikes/disturbances you saw This part in bold is interesting.
I'd be interested in seeing how big this "additional disturbance" was and was it on the powerline or in the analog output of the sonar?
The reasons I'm particular interested is that I'm thinking about putting together the ultimate sonar cable which would include all the knowledge we have to date including using a shielded cable, adding the resistor and capacity, plus a heater for outdoor winter use so I'm open to any suggestions on improvements. Below is a tiny pcb which would hold the resistor and capacity and attach right onto the sonar pins.