Need help for building a meter + control circuit

[frogmaster-riviera]

Hi guys, hope an electronic guy can help me :-)

I'm MD underwater mainly and quite deep, so I have my proper air compressor + Trimix Blinder.

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: O2 Analyser

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.

In a second phase, I'd like to implement a control circuit to avoid Oxygen concentration > 45-50% in the compressor; if the sensor output is > 28/30mv then a light turns ON + a relay stops the compressor.

 

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[airscapes]

If you have the instructions for the non backlite board, use them and get it done. Add an external light to see the LED. An Arduino can be used to monitor a voltage and turn on a light and turn off a relay but there is a leaning curve.

 

[Jason in Enid]

You're building a trimix rebreather?! Damn, even the professional built ones try to kill you. This is like suicide. You're too good of the member to go out like that!

 

[bill from lachine]

frogmaster,

Given the depths you dive to I'd be very careful with this.....better safe than sorry.

Regards + HH

Bill

 

[frogmaster-riviera]

If you have the instructions for the non backlite board, use them and get it done. Add an external light to see the LED. An Arduino can be used to monitor a voltage and turn on a light and turn off a relay but there is a leaning curve.

Thanks Airscape, I waiting for the instruction of the built one... I have googled a lot and I can't find where is the fequency divider on PM-128 board...looks like its r19 and for sure R4 which slightly change de scale adjustment when turned.

First thing is to "fix the analyser" to have the correct scale.

Concerning the 02 alert module, should be possible using an amplifier (x2000) and a comparator with a zender.. Last time I did electronic ws nearly 30 years ago...(!)

 

[frogmaster-riviera]

Bill and Jason

I don't know why people are always thinking it is dangerous to creat our own gas mix...at the end of the day I need the gas SECURE my dives...not using gas mix is less secure (air only) for low depth dives under -150ft or almost impossible deeper then 250ft if you want to remember it because narcosis is to strong.

Most of TEK divers are blending their proper gas mix or for sure have been trainned to do it. It is very simple, as long as you have calculate the "perfect mix" before.

I have a scuba compressor that I have recently upgrade with an isolated chassis (my wife was complaining about the noise), And I have 3x B50l bottle, 2x for oxygen and 1 for Helium. To create a gas mix is very simple:
You use 2 oxygen sensors because helium sensors are very expensive....

air intake -> oxygen injection -> oxygen sensor (mesure and injection adjustment) -> helium injection -> oxygen sensor (mesure and injection adjustment) -> compressor up to 310 bar (4500 psi)

Whatever the place you go/do your blending, it is always based on the method for continuous blending. You can do your mix by bottle transfering but it is less practicle if you want to reach hi pressures over 3000psi.

Here is the blending station I've used for over 10 years now.... we did over 300 deep dives and we are still alive!!!

We always control the final mixture 24h after the blending in the tanks with a different analyser, then we have 3 different sensors and analyser built in our re breather.....

If you want to see the "professional trimix blender" you will be suprized they are the same!!! https://www.google.fr/search?q=melange+trimix&rlz=1C9BKJA_enFR590FR590&hl=fr&prmd=sivn&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiom57sxMvKAhVBVRoKHXR1CkcQ_AUICCgC#hl=fr&tbm=isch&q=stick+trimix

 

[Jason in Enid]

Nothing wrong with mixed gas, but your post sounded like you were trying to build a rebreather, not fill tanks. Do it the old fashioned way, run the gas calcs and fill your scuba tanks. Get a booster to scavenge every ounce of gas from the supply tanks. Fill with O2, add helium, top with air, test and adjust as needed.