Misaligned Logging Speeds Between ADU and GPS / CAN Switchboard

ADU
1

Hi,

I’m still working on my motorbike dynamic logging system, and I’ve come up against a bit of an issue. The high-speed output from the GPS-to-CAN V2 runs at 200Hz, but I can’t log at 200Hz from the ADU to USB - the nearest options are 125Hz, 250Hz and 500Hz. 125Hz will miss data points, 250Hz and 500Hz will result in duplicated data points, but not regularly duplicated, and deciding which data point is properly synchronised with the GPS IMU output will be tricky.

I have a similar issue with the CAN Switchboard, which I am using to add 8 x 100 Hz analogue channels.

Is there a way to get the ADU to log these values to USB at 200 Hz and 100 Hz?

Kind regards,

2

Hi,
Only the preset frequencies are available, and there is no way to change that.

Why do you think it’s an issue?
Even if we had both sides working at 200 Hz, you would still get “duplicated” samples because both devices will never work at exactly the same frequency, even though it says “200 Hz”.

Thinking about it as “duplicated” samples is probably making it worse than it is. A more realistic description is that you are introducing a variable delay to each sample. Let’s assume you have an IMU signal at 200 Hz, where the signal value changes significantly at one point. In a perfect situation, we are sampling the change at the same point where it happens, so there is no delay. In the worst-case scenario, when logging with ADU at 500 Hz, the change occurred immediately after ADU had sampled the signal, and the subsequent sampling would be after 2 ms. That means the samples can be delayed by 0-2 ms.

If a 2 ms delay is significant to you, then a 200 Hz IMU should also not be good enough. The data you start with already has a random delay of 0-5 ms between what is happening in the physical world and the recorded data.

3

just use 250 Hz,

On the other hand, just disable the IMU on bikes, as it was not designed for it, and it won’t work.
I tried the the V1 module, even the GPS was broken with the fusion feature, so I had to disable IMU to get the GPS to work correctly.

I would be suprised, if the V2 module works reliably on bikes.

4

GPS V2 doesn’t use IMU fusion at all.

You get a position fix at 25 Hz from satellites alone.
IMU is entirely independent.

That was the whole point of the new version.
To remove the previous limitations.

5

Thanks to all for the replies. I’ll sample at the next frequency up (100Hz > 125Hz, 200Hz > 250Hz) then work out a way (probably Python) to remove the ‘delayed’ samples and re-time the data to the actual rate. Shouldn’t be too hard.

Thanks again.