Attempting to calibrate the meter in knots

A project log for Cheap underwater tilt current sensor.

Cheap (<$100) underwater current sensor that can be deployed at 70ft depth. Your thoughts, comments and advice are very welcome here!

Max KviatkouskiMax Kviatkouski 07/31/2018 at 06:210 Comments

I've made an attempt to reach out to NOAA seeking their assistance in calibrating the meter but I'm yet to get some answer. Meanwhile, tomorrow I'm going to try to calibrate it manually. Here is the method I'll try to use:

- Tie up my meter to some smooth, sufficiently but not too heavy anchor (In my case it's going to be 5lb dumbbell disk - it's flat and has rounded edges so it will become also sort of a sleigh)

- Tie up front of the disk to my 300ft measurement tape coil

- Lay out, say, 50ft of measuring tape and starting pulling it (trying to make it as consistent and smooth as it is possible doing it manually)

- Check time it took me to retract all 50ft of tape

- Write down timing and time of experiment

- Repeat with slightly different pulling speed

I'll try to make as many experiments as possible air permitting. Hopefully there will be no sensible current tomorrow. Otherwise I'll fall back to mapping the dive site :)

Also I've just received a bluetooth module HC-05. This is for a side project - I'll try to see if it would be possible to download data from the logger over bluetooth right underwater. That would help me to get frequent data updates meanwhile without breaks needed to take the buoy out of water. For my ultimate goal (building a regression model that would let me predict currents at the dive site) frequent data updates are not that important. It's just my impatient bug + desire to share some new insights with local divers frequently.