status - code development

[jerabaul29]

Hi @jvoermans ,

Just some small status updates to keep you up to date :)

• I have been tuning a bit the ADC reading etc. With 5 channels, I can reach up to 100kHz of sustained reading rate. I think that may be much higher than what we need though. So either 10kHz if you think it is useful, or more likely 1 or 2 or 5 kHz, would probably be a good rate. This is summarized here:

https://github.com/jvoermans/Vibration_Logger/blob/master/material_Jean/Due_ADC_reading/src/main.cpp

• I am thinking of the pure logging part. There is no EEPPROM on the Due, so to keep track of the files numbering in case of reboot we have to store some data in flash. Luckily there is a library for this, and this works great. The next point for me is to look at the SD card interaction. The most recend SD card library https://github.com/greiman/SdFat-beta would suggest that reaching writing rates of typically 100 kB/s should be very attainable. This would correspond to 5 channels sampled at 20 kHz, so I think it should be quite fine to write to SD card for any ADC speed lower or equal to 10kHz. There will be a bit of work to make the writing efficient, but that should be fine. I think that the logging of GPS and other instruments will also be non problematic, and I should be able to log this simultaneously to the ADC channels.

So I think that there is no real difficulty ahead, and hope to get something going in the next couple of weeks. I will let you know. The only thing is that you will need some quite big SD cards. If you go for 1kHz with 5 channels, this is 1kHz 5 channels 2 bytes per ADC reding = 10kB per second, i.e. 36MB per hour i.e. 864MB per day ie 6GB per week ie 180 GB per month if I am not mistaken. I suppose we can always use a 256 or 512 GB SD card ^^ . I will have to check how well the SD card library handles these though.

[jvoermans]

Yes, I found the file naming system of the LowLatencyLogger difficult as it has to read files from sd card first in a loop to see if it already exists. In the old system, I was thinking of rather doing the loop, just write a separate txt file with the latest file name in it or something...

I checked the LowLatencyLogger (also based on SdFat) a while back on a 128GB Sandisk Extreme Pro I had around. I had to download some software to format it to fat32 rather than exfat. I tried and logger worked fine, though haven't tried what happens if the 128GB card is half/near full...