DIY Particle Sensor Heating Element Assembly v0.01alpha

The goal of our project is to create the most simple and affordable Heating Element Assembly for the DIY Particle Sensor, at the same time keeping the features of the Nettigo Air Monitor HECA heating assembly: gathering the humidity information before and after the heating, automatic ON/OFF function based on relative humidity level. The assembly must also accomodate colder climate conditions.

We thank developers of Nettigo Air Monitor for their shared knowledge and their incredible work upon which our project is based. https://air.nettigo.pl/

We also thank:

Viktor Antonovich aka @encoded_reality

Denis Kulandin aka @dkulandin

Alex aka @mgw926

Dmitry Petrov aka @petrov1c

Vasily Khoroshilov aka @Ali57m

Alexander Troosh aka @alexandertroosh

Konstantin Golovan aka @KGolovan

Andrew Petrov aka @mrAPetrov

and also https://breathe.moscow/ and https://aircms.online/ projects.

Authors: Dmitry Znikin aka @Dmitry_tsg and IK aka @enhote

To make your own DIY heating element for your particle sensor, you'll need:

1. PTC heating element 10W 20mmx30mm x1 

2. XL6019 Buck-Boost DC/DC Converter x1 https://www.aliexpress.com/item/32788804655.html

3. Sensirion SHT31 Sensor Board x1 https://www.aliexpress.com/item/32700738393.html

4. USB charger 15W x1 

5. Microusb Cable 15W-capable x1  

6. 1/2"-20mm Male Thread Irrigation System Fitting Adapter x1

7. 20mm Irrigation Pipe, 7-8cm in length x1

8. Stainless Steel Scourer x1

9. Silicone Sealant Gel 

First of all you need to put together the Heating Assembly Case. Put the PTC heating element inside an irrigation fitting adapter, add small pieces of metallic scourer to serve as a heat sink. Assemple the adapter together with the pipe as shown on the photo.

Connect the Heating Assembly Case to a Particle Sensor Case by screwing it in. Put the SDS011 air inlet pipe inside the Heating Assebly Case. Fill the spaces with the Silicone Sealant Gel to seal it off and let it completely dry off.

Make a small cut in the pipe to be able to put inside the BME280 sensor. Put part of the BME280 sensor board with the sensor inside the SDS011 inlet pipe.

Secondly we need to assemble the electrical part of the heater. Connect your SHT31 to the same contacts that are used to connect BME280 to the NodeMCU Board. To be able to simultaneously use BME280 and SHT31 you need to solder F2F splitter cables as shown on the photo.

Connect the "AL" output of your SHT31 sensor board to the "EN" input of the XL6019 Buck-Boost DC/DC Converter.

The SHT31 Sensor must be put outside the Particle Sensor Case so that it will be able to correctly measure the humidity of outside air.

In the next and final step we need to connect the power to the XL6019 Buck-Boost Converter and to the NodeMCU Board in parallel. It is convenient to do this by cutting the microUSB cable approx. 10cm before the MicroUSB connector. Clean both usb power cables and solder them to the "IN+" и "IN-" contacts of the Buck/Boost converter. 

Connect the "OUT+" "OUT-" contacts to the PTC Heating Element contacts (in the case of PTC Heating Element, polarity doesn't matter).

The last step is to regulate the outgoing voltage of the Buck-Boost Converter. Do this by rotating the control screw after letting the PTC heating element to heat up for 40-60 seconds, set the voltage to about 7.5-8 Volts.

After Relative Humidity will reach 70%, the Heating Element will automatically turn on. It will also automatically turn off after Relative Humidity will get lower. To be able to use this functionality you need to flash your NodeMCU with Nettigo Air Monitor Firmware.

For questions and critisism feel free to write to https://t.me/s/code4russia

P.S.

We know that the SDS011 orientation on the photos is not recommended. The final version will respect the recommended orientation.