Carbon monoxide (CO) is very dangerous gas, because it doesn't smell, haven't taste. You can't see it, or detect it with your nose. My goal is build simple CO detector. Firstly, I detect very small amounts of that gas in my house. That's is reason, why I don't calculate ppm (for small amounts of CO, you need very precise detector + temperature and humidity has affect on measurement).
Here is my video, you can use ENGLISH SUBTITLES.
Step 1: BOM
Bill of material (affiliate links):
1. Wemos D1 retired
2. MQ2 gas sensor
3. dupont cables
4. AC converter adapter
http://s.click.aliexpress.com/e/cO3r2GFO (don't forget to choose correct plug, EU or USA)
5. cable for upload program to wemos
Step 2: Circuit
In my circuit, Wemos D1 retired is powered from adapter, which consupt 1.5 W from socket. Also, I measure current consumption of gas sensor, which is cca 100 mA
Step 3: Code
You need thingspeak account and in library manager in Arduine IDE Wemod D1 (retired) board.Here is code.
One problem is calculating resistance of gas sensor (Rs), which is incorrect (I got formula from external website). You need to know value of adjustable resistor.
Step 4: Graph
Here you can see sensor values and output voltage of my sensor.
Step 5: Ppm of CO
Here is graph showing how to calculate ppm -> particles per million of individual gas.
Firstly, you need to know R0, which is resistance of sensor at clear air with 1000 ppm of hydrogen. You can write it as R0 = Rs at clear air.
Secondly, you need to know Rs, which is resistance of sensor where is CO gas at some concentration.