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.

 

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.

 

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.

 

Looking at the top pic, its set to DC 200mV fsd, with the solder blobs, its probably altering the resistor chain R14,R19

 

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.

 

Resistors R18,19 look like they are the bottom end of the inputting divider, its probably R19 thats the bottom one and needs increasing.

 

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?

 

If thats the input resistor then it needs to be lowered, try putting a 100k resistor in parallel with it.

Thanks dodgydave..wil give a try tomorrow ;-)

 

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.

 

I have locked this thread pending moderator discussion.

The TS may not feel it dangerous, but most of us disagree.