GPS performance with IMX412 Hires Camera EMI and Mitigation Techniques

[jameskuesel]

Currently I'm trying to get the GPS working on the Starling2 along with a custom airframe. After a bunch of experimentation I'm seeing that having specifically the hires camera (M0161) plugged in and running is causing a noticeable degradation in GPS quality. (Higher EPH, takes longer to acquire satellites/fix, etc.) Assumably, this is due to EMI.

Is this something anyone else has noticed with the hires? I’m hypothesizing it is because it is using proportionally more power and transferring more data (compared to the other cameras) that this is occurring/is more noticeable. 

Besides moving the GPS module further away, are there any other techniques or suggestions Modal has for reducing EMI noise? Namely,

1. Shielding

   • Any materials in specific for wrapping cables or blocking EMI, copper, EMI tape, others?
   • Cables to shield, the gps wire? The Hires Coax, the M0161 itself, the camera board, barrier below the gps module, everything?

2. MIPI Clock rates 

   • Bit of a long shot (I’m not really familiar with any of this) but I read online that sometimes changing the clock rate can help with EMI. Not sure if this an option, would help, or even possible. Wondering if I could apply this to the Hires. Again, a long shot.
   • https://en.wikipedia.org/wiki/Camera_Serial_Interface

Any advice is much appreciated, thanks!

[Moderator]

@jameskuesel That sensor is likely running a clock rate that is similar to the GPS frequency. There is copper foil you can use for shielding which could help

[Alex Kushleyev]

@jameskuesel ,

Can you please provide a bit more detail about your test -- when you enable M0161, how exactly do you test it? Do you view the images using voxl-portal? and if so, how is your starling2 connected to the network? If you are using the wifi dongle, then we have noticed that moving the wifi dongle away from the GPS antenna helps reduce interference. You can test if the interference is still present by unplugging the wifi dongle completely from usb port and use voxl-inspect-cam test application to make sure the camera is running (inspect the same camera stream that you were previously viewing).

Also, please let me know what resolution / FPS you are testing the camera at.

Regarding the MIPI clock rates, i would need to double check, but i believe the IMX412 driver uses 1.5Gbps MIPI bit rate, which is close to GPS L1, but not really close that it would cause interference. We can definitely try different bit rates to see if it helps reduce EMI (if that is indeed the case), but let's first rule out the potential wifi dongle issue. We have ability to change the MIPI clock rate in quite a wide range, but this will require a different sensormodule driver for the camera, which I would need to provide to you.

Another thing, we recently found that the Starling Front End M0173 board may cause GPS interference via the Lepton connection, so if you have that plugged in, please unplug and see if that helps with GPS signal. Lepton needs 25Mhz clock, so one of the harmonics could hit exactly GPS L1 at 1575Mhz.

Alex