I promised an update last week, they say a picture tells a thousand words so I'll save us some time and just show you what I've been up to.
The first prototype pressure sensor cave flood logger has been built:
currently it is sat in a bucket of water in my basement...
The logger uses a ?17 MS5803-14BA fluid pressure breakout sensor module by spark fun, and the logger housing follows a similar design to the cave Perl.
The sensor is potted on the outside of the logger housing in a smaller tube with epoxy resin.
The end caps of the PVC housing were flame treated to oxidise the plastic surface and allow the epoxy to have a better contact surface to adhere to, the epoxy peels off easily otherwise.
Flame treated (left) untreated (right) - water was poured over the top to show how the hydrophobicity of the surface changes.
The new logger is has a plug and play modular design with pin sockets so various modules can be swapped out easily without the need for desoldering, this is useful for troubleshooting faulty modules. The PCB allows for 3 I2C devices, 3 analogue sensors and an ultrasonic sensor to be mounted on the board. An optional screen and/or LED can be mounted for a confidence check the device is working properly.
Once all the tools/components were in place making the loggers was pretty straight forward I made 4 of them last night.
The PCB is mounted within the inner housing tube using some stuff called Sugru, it's kind of like blue-tac but sets as hard rubber and sticks to surfaces well.
I have a few different types of loggers I want to try. the latest is a logger with some buoyancy aids that either hang from the ceiling or are tethered to the floor, the idea being that a flood pulse will cause the logger to move around or change from vertical to horizontal or visa versa. This has the benefit that the sensors are cheaper (?3 each) and the loggers are completely enclosed without the same point of weakness the other sensor designs have. The disadvantage being that the sensors will only tell you if the cave is flooded or not with no transient data. Still useful for seeing the big picture if you have lots of them strategically placed in the various bits of a cave that flood if you want to know how long a cave passage stays flooded for after prolonged rain.
Made a little animation to show you what I mean, I've gone off the ultra sonic sensor a bit, I don't think it would survive submersion and I'm not sure if the bats would like it.