DIY Touch Screen Trimix Analyser

[stevetto]

I think MOD calculated using O2 % is standard function of any analyser with processor, e.g. see https://www.greisinger.de/files/upload/en/produkte/bda/GOX100T_EN.pdf (page 4-5).
I did such option in mine, too (never finished, I stuck to simple voltmeter-like with potentiometer calibration, as I really use standard mixes anyway):

I have used this analyser for a few times but I have never noticed this functionality. A friend of mine has it.
But anyway, MOD display is only a confortable function (mine shows the calculated values for 1.2, 1.4 and 1.6 pO2 without pressing any button) and more usefule for novice divers.
For tec and experienced divers it is not neccessary, especially if standard gases are used.

 

[Jarek Andrzejewski]

GOX-100T (T for "tauchen", which means "diving" in German) has only this option, AFAIK.

 

[stevetto]

Bill of material

WEMOS LOLIN or compatible ESP32 board

3.2 inch 320*240 SPI Serial TFT LCD Module Display Screen with Touch Panel Driver IC ILI9341 for MCU

DC-DC Step Down Converter Module LM2596 DC 4.0~40 to 1.3-37V Adjustable Voltage Regulator


Adjust it to 3V output!

16 Bit I2C ADS1115 ADS1015 Module ADC 4 Channel with Pro Gain Amplifier 2.0V to 5.5V for Arduino RPi

XH 2.54mm connectors and terminals 2 and 4 pins

XH 2.54 cables 2 and 4 pins

MD61 Thermal Conductivity Gas Sensor

CITY AO2 PTB-18.10 A02 AA428-210 or similar Oxygen Sensor

18650 Li Ion battery

18650 Li Ion battery case (serial connected)

10k 1206 SMD resistor
2k 1206 SMD resistor

500 ohms multi turn trimmer potentiometer (Y pattern)

Custom main PCB

Custom sensor PCB

Switch

Molex or an appropriate connector and terminals for the O2 cell. For more info see the sensor’s datasheet.

Links to resources are for your reference only. I do not have any connection to the owners of the shops I listed. You can find most of these components easily on aliexpress, ebay, bangood…. etc.

 

[JahJahwarrior]

The CO sensor used by Cootwo is the S+4 2ECOH, available in UK.

It's too bad you don't have 100% HE near you. I don't imagine you have a store like Grainger nearby, or how much it would cost for shipping, but they have calibration bottles of helium which could be used.

 

[stevetto]

The CO sensor used by Cootwo is the S+4 2ECOH, available in UK.

It's too bad you don't have 100% HE near you. I don't imagine you have a store like Grainger nearby, or how much it would cost for shipping, but they have calibration bottles of helium which could be used.

Thank you for the info. As I see it is only a sensor without temperature compensation. It would make the design more complicated. And it is non-linear.
I might try this one later:
https://www.winsen-sensor.com/d/files/ZE15-CO.pdf


I could buy 100% He from a local gas station but it would cost ~90 USD + tank + shipping.
It is too much for less than 1 m3 He that I can not use later without having compressor or booster pump at home.
That is why used balloon gas for the development (~ 30USD with tank).
For the final calibration only a very small amount of gas would be necessary.
I will solve it somehow.

 

[stepfen]

Bill of material

WEMOS LOLIN or compatible ESP32 board
View attachment 654280


3.2 inch 320*240 SPI Serial TFT LCD Module Display Screen with Touch Panel Driver IC ILI9341 for MCU

View attachment 654281

DC-DC Step Down Converter Module LM2596 DC 4.0~40 to 1.3-37V Adjustable Voltage Regulator


Adjust it to 3V output!

View attachment 654282
16 Bit I2C ADS1115 ADS1015 Module ADC 4 Channel with Pro Gain Amplifier 2.0V to 5.5V for Arduino RPi
View attachment 654283

XH 2.54mm connectors and terminals 2 and 4 pins
View attachment 654284

XH 2.54 cables 2 and 4 pins
View attachment 654285

MD61 Thermal Conductivity Gas Sensor
View attachment 654286

CITY AO2 PTB-18.10 A02 AA428-210 or similar Oxygen Sensor
View attachment 654287

18650 Li Ion battery
View attachment 654288

18650 Li Ion battery case (serial connected)
View attachment 654289

10k 1206 SMD resistor
2k 1206 SMD resistor
View attachment 654290

500 ohms multi turn trimmer potentiometer (Y pattern)
View attachment 654291

Custom main PCB
View attachment 654292

Custom sensor PCB
View attachment 654293

Switch
View attachment 654294

Molex or an appropriate connector and terminals for the O2 cell. For more info see the sensor’s datasheet.
View attachment 654295


Links to resources are for your reference only. I do not have any connection to the owners of the shops I listed. You can find most of these components easily on aliexpress, ebay, bangood…. etc.

Getting nicer and nicer. Well done!!

One question. How do you connect the He sensor to the PCB? I see the connector on the PCB but then how do you attach the wires to the sensor itself? Looking for neat ideas for my project. Cheers

 

[stevetto]

Getting nicer and nicer. Well done!!

One question. How do you connect the He sensor to the PCB? I see the connector on the PCB but then how do you attach the wires to the sensor itself? Looking for neat ideas for my project. Cheers

The sensor has a separate pcb and it is soldered on it.
The small and the main pcb then connected together with wires.
You can see it above.

 

[Miyaru]

Thank you for the info. As I see it is only a sensor without temperature compensation. It would make the design more complicated. And it is non-linear.
I might try this one later:
https://www.winsen-sensor.com/d/files/ZE15-CO.pdf

That one has the same output and specs as the one that I used. Add another A/D converter to read the 0.4V - 2V output from pin 10 on the sensor. I also found that combining the CO sensor output with O2 or He output doesn't work reliably, so that's another reason for using a 2nd A/D converter.
The rest is just software.

 

[stevetto]

That one has the same output and specs as the one that I used. Add another A/D converter to read the 0.4V - 2V output from pin 10 on the sensor. I also found that combining the CO sensor output with O2 or He output doesn't work reliably, so that's another reason for using a 2nd A/D converter.
The rest is just software.

Have you ever tested how linear the output?

 

[Miyaru]

Have you ever tested how linear the output?

For CO: no
For He and O2: yes

The moment I read more than 1 ppm, I won't dive that gas. However, for other applications, a proper calibration would be interesting and that would require a tank of CO.

I have compared the MD62 sensor output with a DiveSoft analyser, same gas flowing through both analysers. Results were very consistent for the usual trimixes.
To compare linearity, a setup would be required where one would start with 100% He and then constantly lowering the He content by replacing it with another gas (eg. N2 to eliminate the thermal conductivity of O2).