At the beginning i though about a small handset and a separated power and
calibration housing. But as always in this project, i was required to
minimize costs, so i designed a slightly bigger handset housing and forced
myself to make all fit in that quite reduced space. That process drove me
completely nuts until the point i was at the very edge to throw the whole
stuff from my second floor in my house several times. And myself after….
In the housing are located:
- 2 magnetic switches
- 1 PIC16f microcontroller
- 1 LM324
- 1 DS1307 clock
- 1 transistor for high current
- 1 pack of 8 AAA NiMh 900mAh
- 1 small lithium 3v backup battery
for the clock
- 1 very low power consumption
(15mA) 16x2 LDC with white char and blue background
- Resistances, capacitances and pots
for calibration, and for contrast of LCD
The controller glands and cable are
from Dev-Pein, a German company that sells very nice things. i decided for a
fixed end in the handset side and a removable one to the lid for pressure
related issues. The fixed is rated to 10 bar and the removable to 8 bar.
The controller does:
before dive mode displays:
- date and time
- time of the last dive (for
scrubber logging info or anything else)
- readings of the cells to check for
- waits and prompts for begin of the
in dive mode:
- ppo2 of all the three cells
- dive time
- ppo2 average value
- status of each cell
- L or H or M depending of the
- Injection character when injection
- alarm characters
it has high and low setpoint
(currently set up at 0.5 and 1.3 bar ppo2) and manual
plus 2 leds for alarms:
- low/high ppo2
- individual cell out of range
-it counts OTU' s, but I'm having
some problems with the CNS%, so i decided not to show them until i am sure
There is a voting logic "algorithm"
in it, set up at 20% difference between cells.
I don’t know whether that is too
much or too few. When there is a higher variation of an individual cell, the
average is taken from the other 2, of course and an alarm is displayed.
2 reed switches control everything
and actually, only one is needed most of the time. the other was thought for
a future deco program for the handset, and for now, it is just a hard reset
button, in case i require that.
I can reprogram the pic as many
times as I want, not needing to extract the pic nor anything. So when
I get inspired to write a better program it won’t be difficult.