Using SDS011 particle sensor with my Android phone

After some testing of SDS011 particle sensor with my laptop (s described in the first post of this series) I realized it is not the most practical way to check for the air quality. I needed to take a laptop with me in a backpack, get it out of it, resume it, connect the sensor using the USB and start the Python3 script (while keeping the lighttpd server running during suspends).

At some point, I realized that I have a quite powerful and much smaller portable computer with me at all times - Android mobile phone. Fortunately, a few months ago I bought OTG cable for my phone.

I found a Serial USB Terminal for an Android phone, installed it and connected the SDS011 sensor to my phone. An application was started automatically and after I started a connection I saw some garbage characters periodically appearing in the terminal output - so, I guessed my phone can read the output from a sensor :)

First tests showed this guess was correct. Initial calculations proved that data fetched from the phone represent correct measurements. Hand-made calculations were made based on the Arduino C code from the joy-it sensor manual:

...
#define LEN 9
unsigned char incomingByte = 0;
unsigned char buf[LEN];
int PM2_5Val = 0;
int PM10Val = 0;
...
if (incomingByte == 0xAA) {
  Serial.readBytes(buf, LEN);
  if ((buf[0] == 0xC0) && (buf[8] == 0xAB)) {
    for (i=1; i<=6; i++) {
      checksum = checksum + buf[i];
    }
    if (checksum != buf[7]) {
      PM2_5Val=((buf[2]<<8) + buf[1])/10;
      PM10Val=((buf[4]<<8) + buf[3])/10;
...

Which means that for the following sequence of bytes:

hex: aa  c0  50  00  29  01  7f  bc  b5  ab
dec:         80  00  41  01 127 188 181

...I did the following math which shows same values I was able to measure using the above mentioned Python3 script on my laptop:

checksum (hex) = 50+00+29+01+7f+bc = 1b5 (which overflows to b5)
PM25 (dec) = (00*256 + 80) / 10 =  8.0
PM10 (dec) = (01*256 + 41) / 10 = 29.7 

After some thinking, I realized this is a good use-case for a new Android application.

"Well, maybe I am not the first one thinking about that.."

I searched for such application on the Google Play. Unfortunately - no such application existed (at least at the time of writing this post).

I searched for Android application on the Internet and I found a GitHub repo for SDS011 Android application - much better. Unfortunately, this application is not published to the Google Play so I needed to build and install it "by hand".

I built and installed this application to my phone using the Android Developers instructions. This is not for the casual phone user, it requires a download and configuration of the Android Studio. However, the end result is nice - thanks to the developers of the SD011 Android app.

After some playing with this app, I found there are some downsides:

• gauges' ranges are not showing proper colours for air quality according to the PM2.5 or PM10 levels
• app doesn't record measurements history

If I find a time, I would like to create an Android application with the following functions:

• save/view a history of measurements
  • date-time & GPS included
  • show location for each measurement on the map
  • this way we can take a ride or walk around the town and later analyze data to see if air quality differs between different locations
• pause/continue measurements
  • this would save the sensor laser & my phone battery
• configure periodic measurements
  • this would save the sensor laser & my phone battery

Cover image & laptop image are created by:

• computergottyt
• Goumbik