This monday evening it was great weather, so I went out to do a first test of my depth sensor. I am using an MEAS MSP-300-100-P-4-N-1, i found it on digikey and cost about 80euros. They have many versions of these sensors. The one I am using takes an input of anything between 9v and 20v and outputs between 1v to 5v depending on how much pressure (PSI) it measures. This sensor is very easy to connect to an arduino, just put the output port on an analog port of the arduino and your are done. I did use an external battery (11.4v) to provide the input power as I found the 9v output from the arduino did not work well.

The Sensor is threaded on an american standard NTP 1/4″, so had to do a little searching to find a threading bit to make this thread in my back plate, but that worked fine. I pre-drilled with a 11mm drill a whole and made the thread. No o-ring was used, just the sensor was tightly screwed in the backplate and it was waterproof :-) (at least for now tested up to 28meters).

I send up a simple program on my arduino that would log the analog output every second so I could analyze the data afterwards. While I was sending my ROV to the bottom of my lake I was able to monitor it on my fishfinder. On the was back up, I stopped at ~24 meters and took a picture of the fishfinder, so I was able to match this data with the ROV log to see how I could calculate the actual depth of the arduino based on the raw data.

When the ROV is above water it was measuring a RAW value of 201 (about 1v), so any addition pressure would have to have this value extracted. Based on my fishfinder data, I was able to calibrate my sensor and came up with this formula for measuring depth (in fresh water).
Depth = (AnalogReadRaw – 201) / 7.585

Leave a Reply