Last time we updated our simple SMOG sensor with display (OLED) and added BME 280 to verify the SMOG measurements – the environmental sensor – as we know that humidity over 70% can add up to the SMOG.
It’s time now to protect our sensor.

Why do we need sensor protection?

Smog sensor – it’s laser in particular – has a limited lifetime – datasheet states 8000 hours. Both the fan and the laser diode should not work continuously – because of wear and tear and also – it clogs the senor with dust. The idea is to  only turn it on when it is really needed – for the time of measurement.
Of course SDS011 supports sleep mode – “software off”, and this is obviously the best and natural way to protect it. I decided not to use it because it is not yet available in ESP Easy 2.0-dev-12, and also because the relay gives us the possibility of turning on an additional element – the inlet air heater, to avoid measuring errors with humidity> 70%, a idea for future extension of the project.

What new things will you need ?

Hardware

• working SMOG sensor from previous entry, the SDS011
• A relay – this example features dedicated relay for the Wemos D1 mini, since it  reduces the number of connections and saves space. And because I just had it lying around, but it can be any relay activated high status 3.3V and powered 5V.
• additional red and

Software

• ESP Easy – already installed in previous step on the ESP8266 which is needed to control our SDS011 sensor

Let’s do it!

Connect anew all the wires – use the schema and pictures. We already know the drill – VCC power on red cables, blue – GND. The new part is the relay.

We connect in accordance with the diagram – please do mind that we change the pins, because of the Wemos D1 Relay shield. CAUTION – do not connect the power supply (+5V) until you make software changes to ESP Easy (below)

New version – our monster grows bigger!

Since we have an additional element that consumes electricity – let’s see how much mA will we need to power the solution:

We can see maximum of 200mA when all elements are active and data is sent over WiFi network. Also – 50mA when relay and SDS011 are off and ESP does not send any data.

Now – let’s move to software – the needed changes in ESPEasy configuration:

• We have to change the pins used to communicate with the I2C bus to D6 and D7, and set the low state at the boot – to make sure the relay is not powered (just in case)

  

• Turn on the Rules in  Tools -> Advanced

  

• Next – change the GPIO port of our sensor to GPIO-15 (D8) – as in the connection diagram:

• We will remove the information about PM2,5 and PM10 from the SSD1306, but don’t worry – this is just temporary we will still display this data, but in a different way

Rules

Time to use new functionality – Rules on ESP Easy. Rules are the way to perform actions, and we can do it in loops. They might also depend on different parameters. We will use them to:

• switch the sensor on after 30 seconds counting from the boot of ESP8266
• Have it running for 120 seconds…
• After 120 seconds – record the data – send them to already known to you Domoticza and InfluxDB/Grafanie for presentation and graphs
• Update the OLED screen
• Wait 720 seconds (12 minutes) and repeat

How? Just paste the script into rules Rules:

On System#Boot do //This will happen at boot ESP8266
   timerSet,1,30  //Set and start timer 1 at 30 seconds
 endon

On Rules#Timer=1 do   //When the timer 1 is up:
  GPIO,5,1            //Turn on SDS011
  timerSet,2,120      //Wait 120 seconds to spin it up
endon

On Rules#Timer=2 do  //When the timer 2 is up
  SendToHTTP 10.20.30.40,8080,/json.htm?type=command¶m=udevice&idx=11&nvalue=0&svalue=[SDS011#PM25] //Send the PM2,5 data to Domoticz
  SendToHTTP 10.20.30.40,8080,/json.htm?type=command¶m=udevice&idx=12&nvalue=0&svalue=[SDS011#PM10] ////Send the PM10 data to Domoticz
  OLED,2,1,PM2.5: [SDS011#PM25] //Update OLED with PM2,5
  OLED,3,1,PM10:  [SDS011#PM10] //Update OLED with PM10
  GPIO,5,0                      //Turn off SDS011
  timerSet,1,720                //Set the next cycle at 720 seconds 
endon

This is how it looks (comments in Polish from older screenshot):

Note that the script lines will display the measured values on the OLED screen – only the ones that will be measured (otherwise when SDS011 is  switched off – we would see ‘nan’ values).

Now create in Domoticz (Check out the the “dummy sensor creation” sensor entry) virtual sensors – separately for PM 2.5 and PM 10. Use the “Custom sensor” from drop-down list. The Rules scripts assumes the IDX values of  11 and 12 – change it to yours, just as the IP address and port of the domoricz.
Power on our sensor and observe the first data after around 16 minutes of running:

The final move is to configure data connection from Domoticz  InfluxDB and Grafana. Another option is to send the BME280 data – and I suggest to do it every 5 minutes. Our sensor is ready!