As usual this is a project for my brother, but this time it was actually me that came up with the idea. My plan was to have an array of temperature sensors hanging below a buoy measuring temperature every meter down to 10 meters.
But this was nothing new my brother informed me and what I built is similar to things like these.
(but for a fraction of the cost)
http://www.nexsens.com/systems/temperature_profiling
http://www.pme.com/HTML%20Docs/TChain_Home2.html
I have worked with the DS18B20 temperature sensor before and it is an 1-wire device that has a laser cut unique address so you can have as many as you like on a single 1-wire bus. My first thought was having a cable with 3 wires, for 5V, GND and data. After goggling a bit it turns out that a regular CAT5 cable is the way to go.
But how to waterproof the sensors?
My first plan was to solder the sensors directly to the wire. Luckily I decided to make a breakout board to make the mounting of the sensors easy. As the CAT5 cable has 8 wires 4 would be used for the sensors and the remaining 4 would act as tension relief.
My first thought was just to solder the sensors in and paint some epoxy over it to waterproof the sensor. But instead I went for a silicone mold and encapsulate the whole sensor in Epoxy.
My breakout board
First making the master for the mold
I used FIMO modeling clay and baked to make the master
Then a container to hold the silicone
Then the silicone
The silicone worked great with the Epoxy as it needs now release agent and pops right out
In the end I had my array of sensors
The Arduino data logger is mounted inside a waterproof box. It has my data logger shield on it so this rig should be able to take a measurement of the complete array every 10 minutes for about a month on a regular 9V battery.
PS. I have sent a mail of to Sparkfun to see if they are interested in selling the shields. It might be a long shot, but why not?
