Poor Man’s Haze Monitoring

The haze in Singapore reached record levels last month, hitting a 3-hour PSI reading of 401 on 21st June. Many of us were a little disappointed at the “laggy” PSI reports provided by our National Environment Agency, and some enterprising people have decided to take matters into their own hands. That included me. We are going to build our own haze monitoring gadget.

Several options were available, including a very respectable laser particle counter that’s somewhat like those VESDA (very early smoke detection apparatus) systems used in data centres. Well, I decided I wasn’t going to invest that much money. After some research, I decided to get the dust sensor pictured above.

It’s not quite the same as a particle counter. The way it works is by measuring reflected energy from particulate matter that passes through IR light that has been focused on a sensing point. A heater creates an updraft so that there will be a volume of air passing through.

That actually sounds better than what NEA’s apparatus does. NEA’s setup has particulate matter sticking to a filter, which weakens a beta ray that’s passed through it. The weakened beta ray intensity tells how much particulate matter there is.

This sensor is already being tested. It’s connected up to an Arduino, which sends its reading directly to my Linux box. Ideally, I want the solution to be self contained. So the next step is get the Arduino connected to a Raspberry Pi over I2C. I’m also exploring the idea of the dust sensor wired directly to the Raspberry Pi, but there are two challenges. The easier one is the conversion between 3.3V and 5V logic levels. The other one is about accurate timing measurements on the Raspberry Pi.