@bytesnz

Jack Farley, Computer Engineer

I have been wanting to attach a camera to a litter picker to track the things I have been picking up for a while. Hopefully, I can then use the images to track the items I'm picking up. As the Great British Beach Clean week is around my birthday, I decided to treat myself and spend some time on the project.

The Hardware

I bought a Raspberry Pi Zero W and a camera when they first came out, but hadn't really done anything with them.

As I was planning on using them for a beehive monitor, I also bought a 5000 mAhr LiPo battery and a PowerBoost 1000C LiPo battery module to use with the pi and a solar panel. I soldered them all up (minus the solar panel) and strapped them to the litter picker I had in a high-tech housing (a quarter of an orange juice bottle). I also bought a NEO-6MV2 GPS module so that it could record the GPS position the photo was taken.

I wanted to have the pi take a photo automatically when I went to pick something up and was planning on wiring up a microswitch, like one I replaced in my mouse surgery, but didn't have any spare. I instead decided to use some nickle tape I purchased to replace the batteries in my laptop.

I used an old USB cable that someone had thrown out and soldered two strips of nickel tape onto two of the wires in the cable.

I then placed old packaging foam between them and taped them together with trusty old electrical tape.

The Software

I downloaded the latest version of Raspberry Pi OS Lite and loaded it onto the microSD card I had.

$ wget https://downloads.raspberrypi.org/raspios_lite_armhf_latest -O raspios.zip
$ unzip raspios.zip
$ sudo dd if=2020-08-20-raspios-buster-armhf-lite.img of=/dev/sdb

I then configured the Pi to automatically connect to my WiFi using wpa supplicant and enabled ssh to start automatically

$ wpa_passphrase wificentral
$ echo "
network={
  ssid="wificentral"
  psk=6862a1eb9ac83930997165f51817a1cffea8da6bbbb24316d0efd181588ee93c
}" | sudo tee -a /media/user/rootfs/etc/wpa_supplicant/wpa_supplicant.conf
$ sudo touch /media/user/boot/ssh

The first blog I looked at on using a NEO-6M GPS module with a Raspberry Pi used Node.js, and as I am a fan of Javascript, I thought yeah, why not.

I installed the modules GPS.js and node-serialport for dealing with the GPS module, pigpio for detecting trigger presses and pi-camera-connect and piexifjs for capturing images and adding metadata to them.

I found the node-serialport and GPS.js modules had changed since the blog was written, so I had to rewrite the code and also found the GPS was on device /dev/ttyS0 instead of /dev/ttyAMA0.

const file = '/dev/ttyS0';
const GPS = require('gps');
const SerialPort = require('serialport');

const port = new SerialPort(file, {
  baudRate: 9600,
  parser: new Readline({ delimiter: '\r\n' })
});

const gps = new GPS;
let position = null;
let updated = -1;
 
gps.on('data', function(data) {
  if (data.type === 'GLL' && data.valid) {
    position = data;
    updated = (new Date()).getTime();
  }
});
 
port.on('data', function(data) {
  gps.updatePartial(data);
});

After some playing around with camera options and adding the metadata into the images, I was ready for my first tracked litter pick.

A little dark as it was early evening and in need of some angle adjustment, but it worked as I hoped.

As a finishing touch for the first version, I created a SystemD service to start the Node script on startup and got the script to save some power by turning off the WiFi 1 minute after startup if it wasn't connected to any network.

Helpful hint, when doing this, make sure your logic is correct as iwconfig wlan0 txpower off persists even after a power cycle. Doh!

It was now ready for proper litter picking session.

I have put the code up on Gitlab and will update as I add more functionality. Ideas so far have included:

• a WiFi hotspot to track litter as you pick
• automatic uploading and tagging of images when it connects to the internet.