I did a little research. MQ-135 Sensor detect air particles from 10ppm to 300ppm (1000ppm benzene). 10ppm is high value - I think it is more applicable to alarms.
So we need more sensitive sensor. TSG 2602 works from 1 to 10ppm - it is much better.
It seems that these sensors are more suitable for measuring indoor air quality. In datasheets don’t see information about sensitivity to S0x, NOx, C0x …etc, despite I think that because of their general sensitivity, will work in outdoor environment.
I created wiring diagram (see attachment, but circuit is untested) and formula for temperature compensation - these gas sensors is sensitive to temperature and slightly to humidity.
Schema is taken from hobby-boards Temperature/Sun sensor. I do not know whether I chose the optimal resistor values, but trimmer solves everything.
Compensation formula (only for TSG2602):
Vcomp = Vin*(-0,028*T+1,6)
Where:
“Vin” is meausred voltage
“T” is Temperature in Celsius deg
Then for implemenation to SW is also needed know voltage for clear air (0,9~xV - depends on trimmer position) and voltage for contamined air (0.11V~xV depends on trimmer) - it will be simply readed from OneWireViewer.
Probably in the near future I’ll try to order parts and test it.
EDIT: Added URLs, fixed bad ppm values (oh my memory… :))
I don’t think that the amount of Ozone refers to the overall air quality. Respectively for high value of ground ozone must be present hydrocarbons and/or nitrogen oxides (both present eq. in exhausts) and must be high solar radiation/activity. I think that Carbon Dioxide sensor will be closer to overall air quality.
Nevertheless, these sensors have low sensitivity - at least I think - It starts from 10ppm. See datasheet for MQ 131 or MQ 135 and others similar.
TSG 2602 arrived yesterday (bought at rs-online.com).
Works very well. Detects cigarette smoke, some fumes, VOCs etc… :hello1: I modified the scheme for maximal sensitivity. See attachment.
The output voltage depends on the quality of air and is between approx 0,4 - 4,7V.
Now we need support for Air Quality sensor in WD.
If possible:
field for AQ ROM at 1-Wire reader in “Main setup” tab
Checkbox for AQ sensor temperature compensation - on these measured values will be applied temperature compensation for TSG2602: Vout = Vin*(-0,028*T+1,6) where: “Vin” is meausred voltage and “T” is Temperature in Celsius deg. Or this checkbox may be replaced with field where will be added equation for specific sensor.
Output can be Air Quality index (check box in 1-wire reader):
configuration at 1-Wire reader in “Other settings” tab where will be fields for minimal and maximal voltage.
Air Quality Index = (Vmax-Vmin)/500*(Vmax-Vact) where “Vact” is actual measured value.
New column “1_wire_Air_Quality” for WDMySQL
WD Graphs for AQ
WD Main window may include AQI number and status word.
And then we have another weather value that can be measured and used in WD. 8)
With this sensor can be measured a Particulate Matter (PM10 or even smaller particles). But reading data from this sensor isn’t easy (10ms pulses). How did you solved it? Do you have a schematic?
The sensor should be optimally placed at a height where they move people. About 2 meters above ground.
Sensor must be also well ventilated, not only because they need good air exchange for measuring, but because of its inner portion is heated up to 400 deg C - temperature of sensor surface is about 50 deg C in room temperature. So if is gas sensor placed into a small box with poor heat exchange without temperature sensor (for calculating of heat deviation), measuring will be very inaccurate.
Looks like an interesting project that, if I can find the time to implement this also at my location where we have an interesting environment here on the island of Maui, Hawaii. We get some SO2 from the volcano when the winds are coming from that direction to pollen in the air all year around…
I will follow this project as it develops.
BTW, Brian is away from his home with his children’s camp for the past week. He should be back this weekend.