Basic board prototype for the unit. 3 pots to simulate o2 depth and battery level sensors, ds1307 realtime clock on an i2c interface, 16x2 lcd display and pic 18f4550 running the pinguino botloader.

More thoughts on the amazing DIY bendomatic

So after much effort I've got a rough prototype working here - on a piece of wood with simulated sensors.
Pinguino uses a lot of memory in the pic but does enable swift development although the i2c library is rather big... may rewrite this to make it smaller

Pics up soon
..

DIY Dive Computer

Is it really possible to build your own dive computer these days ?
I aim to find out.
Algorithms are readily constructed from the published Bulhman data.
Very useful background materials are available at
 http://www.lizardland.co.uk/DIYDeco.html
&
liquivision.com/docs/mvalues.pdf
&
liquivision.com/docs/deepstops.pdf

So a simple algorithm  is easily derived.

So far I've benchtested a system using a pic 18f4550 coupled to a ds1307 i2c realtime clock, and a simulated MPX5700A pressure sensor.

MPX5700 gives 0.2V+0.64V/bar output voltage when driven with a 5V bias so my simulation consists of a 10k pot across the 5V rails to generate a fake sensor voltage.

I'm running test 'dives' by adjusting the pot and watching the output usinng a 16x2 LCD driven off the pic.

I'm fixing the fo2 at 0.21 for air diving at present and using the ds1307 to give accurate timing.

At present the dive starts the moment the pic is powered but future dev will sort this out and use a combination of wet contacts and the pressure sensor to start a dive.

I'm hoping to compare outputs to a set of test profiles generated from mplan someday.