Nitrox/Trimix & CO analyzer

[ScubaBunga]

Battery-operation is indeed a requirement.

I'm looking into using the 18650 battery as well, including a charging option. With the recent live aboard disasters in mind, such a simple analyzer could be a personal CO detector as well. E.g. adding a buzzer that sounds when the CO level goes above a certain value.
At the same time, that battery should never become the cause of a possible fire....

Mine uses an 18650 and a little 5v boost chip like the ones in the charger packs. I added a bit to the program to read the battery voltage so I know when I need to recharge. With the chip, a little logic, and transistor it also shuts down before battery is drained to low. It has a mini usb for simple charging. Works great.

 

[ScubaBunga]

It's even easier than that. The ZE07-CO needs a 5V power supply and provides one DAC output. The output is connected to an analogue pin of the arduino.

I just ordered two of these. The stats and ease of use look better than the SPEC sensor I originally used. Shipping will be another month it seems with continued slowness due to covid.. but hopefully not too long.

 

[Miyaru]

I just ordered two of these. The stats and ease of use look better than the SPEC sensor I originally used. Shipping will be another month it seems with continued slowness due to covid.. but hopefully not too long.

Consider using an ADS1115. The Arduino's built-in AD converter is lacking precision, depends heavily on the voltage reference. The original code I referred to (uses an analog port + Vref) is only reliable when this sensor is the only connected device.
If you combine a O2 sensor and CO sensor, use a single ADS1115 with a differential reading (0,1) for the O2 sensor and a differential reading (2,3) for the CO sensor.

 

[ScubaBunga]

Consider using an ADS1115. The Arduino's built-in AD converter is lacking precision, depends heavily on the voltage reference. The original code I referred to (uses an analog port + Vref) is only reliable when this sensor is the only connected device.
If you combine a O2 sensor and CO sensor, use a single ADS1115 with a differential reading (0,1) for the O2 sensor and a differential reading (2,3) for the CO sensor.

Yep already use them. Will just replace my sensor and update the code to match.

 

[Miyaru]

First prototype ready. Nitrox, Trimix and CO all in one.

 

[Miyaru]

 

[Miyaru]

The last picture shows elevated CO level. The analyzer has a buzzer with annoying beeps that will wake you up.....

 

[1isNone]

At the same time, that battery should never become the cause of a possible fire....

Given the rechargeable tech we have today, is "never" possible?

 

[RX8Bob]

This has me really really wanting me to build an analyzer now. I have far too many Raspberry Pi, Arduino, and ESP-32 laying around waiting for a project... Any thoughts on using an ESP-32 and creating a phone app via bluetooth or WiFi?

Funny this comes up because I just took a few tanks out of storage after sitting for awhile (Still in hyrdo though) and wondered if they had rusted at all. Brought them to a local shop, used an analyzer to verify since I didn't want to drain then refill the doubles (impatient), then dove. Had I had my own analyzer, would've saved a ton of time.

 

[Miyaru]

Sharing the work done so far. The schematic in pdf (otherwise it'll be resized too small by the board).

Few notes:

• The current schematic will drain a 9V battery block in roughly 2 hours. The MD62 sensor consumes a lot of power for heating, the Arduino requires >5.5V on the Vin pin and turns the rest into heat.
• There are only 2 interrupts on the Arduino, which is why there are (only) 2 buttons. Shearwater computers use only 2 buttons as well, so this one works the same.
• Only the minimal code for the display is in here!
• Code comments are minimal. This is not a tutorial, nor a copy-paste code for creating an analyzer. Program your own menu and screens.
• Libraries might have changed. Change the code accordingly.
• Code is separated into multiple posts due to max post length.

#include <RunningAverage.h>
#include <EEPROM.h>
#include <Adafruit_ADS1015.h> // AD converter
#include <Adafruit_GFX.h>     // Adafruit core graphics library
#include <Adafruit_ST7789.h>  // Adafruit hardware-specific library for ST7789

#define TFT_CS    10  // define chip select pin ST7789 TFT module
#define TFT_DC     9  // define data/command pin ST7789 TFT module
#define TFT_RST    8  // define reset pin, or set to -1 and connect to Arduino RESET pin
#define OLED_RESET 4       // Reset pin # (or -1 if sharing Arduino reset pin)

Adafruit_ADS1115 ads(0x48);    // analog-digital converter for oxygen and helium sensor
Adafruit_ADS1115 ads2(0x49);    // analog-digital converter for CO sensor
Adafruit_ST7789 tft = Adafruit_ST7789(TFT_CS, TFT_DC, TFT_RST);

// -------sensor settings-----------------
boolean enableHe = true;
boolean enableCO = true;

const byte calibrationCount = 10; // calibration samples
const byte readDelay = 3;          // ADC read delay between samples

float oxVcal = 0;      // oxygen voltage - calibration
float oxVact = 0;      // oxygen voltage - actual / measured
float oxVmax = 0;      // oxygen voltage - max
float oxVmin = 0;      // oxygen voltage - min
float heVact = 0;      // helium voltage - actual
float heVmax = 0;      // helium voltage - max
float heVcal = 0;      // helium voltage - calibration | turn potmeter so it reads 0mV
float carbon = 0;      // ppm
float coVact = 0;      // carbonmonoxide voltage - actual / measured

float gain = 0.03125;         // gain ADS1115
unsigned long time;           // runtime
unsigned long menuCounter=0;  // runtime

float MODcalc = 1.4;      // start with 1.4 for MOD calculation
const byte bLeft = 2;     // pin D2 connected to pushbutton
const byte bRight = 3;    // pin D3 connected to pushbutton

volatile byte buttonStateLeft;
volatile byte buttonStateRight;

byte leftclick = 0;
byte rightclick = 0;
byte action=0;
byte RAsize=20;
byte i=0;
int16_t adcHe;
int16_t adcO2;

boolean calibrateHe = false;
boolean calibrateO2 = false;

char calibrate[] = "Calibrating...";  // create a string
char calibOK[]   = "Calibration OK  ";
char calibReq[]  = "Calibration required";
char mV[]        = "mV  ";
char space1[]    = " ";
char ver1[]      = " Nitrox / Trimix";
char ver2[]      = "Analyzer software";
char warn1[]     = "This analyzer";
char warn2[]     = "has no brain!";
char warn3[]     = "Use your own!";
char HEsensor[]  = "He sensor ";
char O2sensor[]  = "O2 sensor ";
char next[]      = "Next";
char select[]    = "Select";

RunningAverage RAhe(RAsize);       // average He with 20 values
RunningAverage RAox(RAsize);       // average O2 with 20 values
RunningAverage RAco(RAsize);       // average CO with 20 values

float readO2sensor(){
  RAox.clear();
  float millivolts = 0;
  for (i=0; i<=RAsize; i++) {
    millivolts = ads.readADC_Differential_2_3();
    RAox.addValue(millivolts);
  }
  millivolts = abs(RAox.getAverage()*gain);
  return millivolts;
}

float readHEsensor() {
  RAhe.clear();
  float millivolts = 0;
  for (i=0; i<=RAsize; i++) {
    millivolts = ads.readADC_Differential_0_1();
    RAhe.addValue(millivolts);
  }
  millivolts =  abs(RAhe.getAverage()*gain);
  return millivolts;
}

float readCOsensor() {
  RAco.clear();
  for (i=0; i<=RAsize; i++) {
    coVact = ads2.readADC_SingleEnded(3);
    RAco.addValue(coVact);
  }
  coVact = abs(RAco.getAverage()*0.1875)/1000 - 0.015;
    float ppm = (3.125 * coVact - 1.25) * 100;  //linear relationship(0.4V for 0 ppm and 2V for 500ppm)
   if(ppm<0)
     ppm=0;
   else if(ppm>500)
     ppm = 500;
   return ppm;
}