Oxygen Analyzer & Alarm for DIY Trimix Blender... scuba diver welcome

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frogmaster

Joined Jan 25, 2016
5
Hello to all

I'm currently building a Trimix blender to have the ability to create my gas mix for scuba diving.

I have found some diagram and DIY project on oxygen analyzer based on the PM-128A LCD module: http://dive.hemnet.com.au/projects/o2analyser/o2analyser.htm

My Blender is based on 2 oxygen analyzer using Teledyne R-17 Oxygen sensor : http://www.teledyne-ai.com/pdf/r-17med.pdf.

I would like to use PM-128E (EBL) for the backlight feature of this LCD meter compared to the regular PM 128A... little problem is that the board layout slightly differs beetween the the PM-128A & PM-128EBL (!) ...and I'm lost.

I try to find where I can change the scale of the panel to read 20.9 when I have an input of 12.4mV from the Oxygen Sensor + implement a potentiometer to calibrate the sensor.


 

Thread Starter

frogmaster

Joined Jan 25, 2016
5
Thanks but I don't play with my life and there is always a double check on the field with an other analyzer, plus the analyzer that we have in our re breather.

There is no "professional" blending solution, all of them are almost DIY.
 

Dodgydave

Joined Jun 22, 2012
8,393
Looking at the top pic, its set to DC 200mV fsd, with the solder blobs, its probably altering the resistor chain R14,R19
 
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Thread Starter

frogmaster

Joined Jan 25, 2016
5
I am inputing 12,4mv and i read 12,4mv.... but I'd like to read 20,9 = normal concentration of oxygen in the Air.
I'd like to change the scale of the display.
 

Thread Starter

frogmaster

Joined Jan 25, 2016
5
R19 seems to be the one in touch with the "200mv" strap. Value is approx 0.543MΩ

I need to change the conversion factor to increment 1mV for every 0.5mV.
Vref = 1000 x (actual voltage/scale voltage) or 1000 x (10.45/209) 10.45mV Sensor reading of air, and 209 the voltage you want to see on the display. This equates to 50mV. (1000 being the internal clock period). .... this theory, now how can i do it?
 
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spinnaker

Joined Oct 29, 2009
7,815
You are asking random strangers to help you bet your life. Even if there is somebody here that can be helpful, don't forget who's life hangs in the balance.;)

This thread needs to be locked. Anyone trying to help out on this project is being totally irresponsible or is not aware of the extreme danger involved in SCUBA when wandering outside very well defined procedures.
 
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