Water meter reader

thingiverse

I wanted to read data from my analogue water meter using an Arduino. The water meter has a small cog wheel made of reflective material. Just check out these images. Initially, I thought about illuminating this wheel with a bright light source and detecting the reflected light. After lots of experimenting, I had to scrap this idea because the cog wheel didn't reflect light uniformly for each tooth. Some teeth reflected light towards the sensor while others didn't. Next, I decided to measure the reflected light intensity of one red arrow. The arrow with 0.001 scale measures 1 liter each turn. A green super bright LED was used to illuminate the water meter display and a photo transistor with a simple amplifier detected the signal. It's essential to use a green LED because it's the complementary color to red. The red arrow will absorb most of the green light while the white background will reflect most of it. My first attempt without any dedicated optics resulted in unstable results. After fiddling with screws, I decided to attach a simple lens. However, all lenses I found were quite expensive and hard to find one that fits my small diameter needs. But there's a cheap and effective alternative on eBay - a complete camera replacement module for just 3€ for a Samsung smartphone "Samsung S8500 Kamera Kameramodul GT-S8500". I think any other smartphone camera module will do this job. You'll need to disassemble the entire camera module, and only use the lens. The result was quite good - I could see a strong signal on my scope (between 2.5V and 3.5V while the red arrow turns around). The complete design consists of the water meter sensor device, a box for electronics, and the electronics itself. You'll need two threaded rods (ca. 80mm length and 3mm diameter), 2 M3 nuts, 2 M3 locking nuts, and a few washers. I reused an old USB-A socket that I glued into the water meter cap to lead electrical connections out of the sensor. Some heat shrink tube is also very useful. Building Instructions: Assembly: Print all parts first. Put an M3 nut into the opening of the parts called SensorPhotoTransistor and SensorLED. Put these two parts into the water meter main part. Slide rods through holes in the main part and the parts with nuts. Attach knurled knobs to rods. Slide washers over rods on the counter side and secure each with a locking nut. Lens Holder: Disassemble camera module. The lens system is a small disk 2.5 mm height, 4mm diameter. Remove copper wire around the lens as we don't need it. Put the lens into the opening of the lens holder. Slide the lens holder into the sensor with the photo transistor. Soldering: Solder the 150 Ohm resistor to the LED, attach wires and use heat shrink tube for electrical isolation. Solder the other end of wires to the USB socket (see SV3 in image). Do the same with the photo transistor. Gluing: Slide the photo transistor into the part SensorPhotoTransistor and the LED into the part SensorLED. Use some glue to fixate parts. Glue the USB socket into the WaterMeterCap part. I used sugru for it. Glue the WameterUSBCover onto the cap. Soldering Board: Solder the amplifier board and put it into the electronics case. Attach all cables. Installation and Calibration: Attach the device to your water meter. Turn on power for electrical components. Move the photo transistor sled with one screw until it directly points to the tip of the desired arrow. Move the LED so that the white background is very well illuminated. Use a multimeter or scope to monitor output signal. Let some water flow because we need the red arrow to turn slowly. When the red arrow is under the photo transistor, you should see voltage increasing. Move sleds until you get an optimal signal. You can also turn the whole device a little bit (just a few degrees). Now you must close the device to prevent environmental light from falling into the sensor. Additionally, it helps to minimize fogging of the water meter cover glass. You may add some silica, too. If you have a good signal, you're done. Attach a micro controller and evaluate values. Use some paint to mark the position of the device in relation to the water meter. Now you can remove and easily reattach the water meter reader for manually reading. Water Meter Reader Completely Assembled: Use some paint to mark its position