Most of the analogue oxygen controllers are well designed, easy to build and reliable,  but they have 2 disadvantages:

 

• They usually have to be manually  calibrated.

   

• They usually are not equipped with alarm functions.

   

 (alarms have a negative aspect too; they tend to increase the vigilance of the diver..)
 

This project has been made  possible thanks to communication on the Internet!
It is the result of sharing  an experiment, competences and
friendships. Without the Internet it would never have become such a success!

Thanks to all sharing knowledge and information!

 

The shared idea was to build a programmable oxygen controller with following characteristics:

 

- Simple and innovating

- Compact ( you will see that that was a hard thing to realise)

- Build with basic tools in a garage

- Simplified Calibration without the need to open the rebreather

- Fitted with alarm, monitor, and a vibrating warning device

- Large LCD screen

- Design with batteries in external container.

 

 

Electronics:

Since I am not an electronics specialist I use a component that is easy to program (directly on the PC) and using a  simple  interface called : the PICBASIC from Comfile Technology™.
http://www.comfile.co.kr/english2/pb2000.html
This component has converters, analogical/numerical 10 bits, necessary to the measurement of the PPO2 on the 3 cells, the entries for switches and exits which makes it possible to control the led's, a buzzer, and a vibrator.
For this project you will need:

 

- 1    pc        5 volt power supply

- 3    pc        amplifiers OP.

- 1    pc        Pic integrated circuit.

- 1    pc        buzzer

- 3    pc        led’s

- 1    pc        alarm vibrator.
 

 

The principle is very simple;
 

1 The cells are having an output of 10 mV in air

Since this voltage is very low it is necessary to amplify it with an amplifier like the model OP.
2 This voltage is added to a  programmable PIC which transforms the voltage into digital and one
displays the result on a display.

 

Software:
The PICBASIC is programmed in BASIC. 

Display, interface:
I have chosen a digital display showing four times sixteen lines.
Beware, this is very important since the lines decide how big the housing will be.

first line: showing the pO2 of the 3 cells.
second and third line: a bar graph which indicates the average pO2.
fourth line: operating time (with a beep all 3minutes) and a message (low, high, ok or what you want.)

The case: the most complicated part of the project.

At the start of the project I had thought of building an epoxy case (moulding). Unfortunately I did not succeed in making a functional model. After this I decided it had to be made by CNC routing, but unfortunately I do not own such a machine! Bernard M. living in Swiss brought the solution and proposed to made the housing for me. I gave him the dimensions of the housing and the position of the magnetic contacts. In the design process we defined a maximum diving depth of 80m for the housing.
We then performed data-processing simulations and used constrain techniques to define the minimum thickness of the walls in POM..... that gave us the external dimensions of the housing. These design aspects took us 6 months,  but the results where exceptional!
Now we have quality made  in Swiss thanks to Bernard!

Operation:

1) starting: remove the magnet hold by elastic cord! It is not beautiful but it is efficient!
2) a message appears asking to confirm the start of the calibration.
3) then the user decides if oxygen or air is used for the calibration.
4) the choice has to be confirmed.
5) calibration starts.
6) posting the results of the measurement. The handset asks to confirm the measured values.

7) acceptance of measurement and switch to dive modus.

 

After this point it is not possible to stop the unit to get into dive modus unless you use the external magnet to switch the handset off. 

Reliability:
 

The unit is in a test phase.
The alarmvibrator is a very nice and functional warning system.
Led’s are hard to see.
Autonomy: no the problem.

Test results: to be processed

 

Further development:

 

Realization of an analogical oxygen controller 

Realization of a HUD.
Realization of a version ECCR.
Realization of a more compact version.....

 

Thanks for your attention; Philippe Combis.

 

WWW: http://archicom.chez.tiscali.fr//indexida.html
mail: philippe_combis@(no-spam)yahoo.fr

Update 2006

Update august/september 2006