The ETA on the custom depth gauge is around October. The electronics will be identical to the technology I used in the near infrared spectrophotometer I developed in 2002 to measure muscle oxygenation during exercise--the only difference is that instead of a 10 billion gain photodiode there would be a pressure sensor and a loudspeaker. Be warned though, the device is around as big as a Mares Apneist, and it is encapsulated in solid epoxy, with an embedded rechargeable battery (i.e. looks a bit funky). The battery only lasts for about 8 hours and for that reason it must be recharged pretty much the night before.
For the freediving decompression, since we do not know the next target depth of the diver, the plan was to display a field called 'max allowable depth.'
Example:
You dive 30m for 2'00"
As soon as you surface, the computer says:
Max Allowable Depth: 10m
[i.e. max allowable depth if you left at this instant and dove for the preset time, for example 2'00"]
Then, some seconds later, it shows:
Max Allowable Depth: 15m
This keeps increasing as you offload your nitrogen.
After a 100m dive for 3'30", it would read:
Max Allowable Depth: 0m
And it would keep reading that pretty much for the rest of the day.
So, if you wanted to do repeats to 30m for 2'00", then step #1 would be plug it into your PC and program 2'00" as the preset average dive time. Then, dive to 30m, and then upon surfacing, you wait for the max allowable depth to read 30m again (probably take about 5 minutes).
Suppose the computer, at one instant, says 'max allowable depth: 20m', and you start a dive and descend beyond 20m. Then, the crazy decompression warning alarm goes off, which tells you to ascend immediately and finish the last 10m very slowly if possible.
Another drawback is that the device has no buttons. The only way it can be programmed is via the PC interface. It can be turned on by shorting out two pins which protrude from the epoxy encapsulation. I'm thinking of other methods to turn it on and off.
The whole point here is that if you don't have $2,000,000 to build a truly custom ASIC driven depth gauge with custom casing, you can build one with pretty much stock electronics, but the casing and interface are a bit 'funky.'
The main thing I like about it is that I should be able to see my depth at all times in dark water, without having to shine a light on the gauge etc... or mess with some hard to push light button.
I could finish this gauge way before October but I have some other projects I'm working on at the moment.
Eric Fattah
BC, Canada