Water meter reader

thingiverse

I wanted to read the data of my analogue water meter with an arduino. The water meter has a small cog wheel made of some reflecting material. Just have a look at the images. The first idea was to illuminate this wheel with a bright light source and detect the reflected light. After a lot of experimenting I had to drop this idea. The problem was, that the cog wheel did not reflect the light uniformly for each tooth. Some teeth did reflect the light to the sensor while some other teeth did not. So the next idea was to measure the reflected light intensity of one of the red arrows. The arrow with the 0.001 scale measures 1 litre each turn. A green super bright LED was used to illuminate the water meter display and a photo transistor with a simple amplifier should detect the signal. It is important to use a green LED because green is the complementary color to red. The red arrow will absorb most of the green light while the white background will reflect most of it. The first try without some dedicated optics resulted in a not so stable result. After a lot of fiddling with the screws I decided to attach a simple lens. But all lenses I could find were quite expensive and it was very hard to find one that fits the small diameter I needed. But there is a cheap very effective alternative on eBay. I found a complete camera replacement module for just 3€ for a samsung smart phone "Samsung S8500 Kamera Kameramodul GT-S8500". http://www.ebay.de/itm/252821221343?_trksid=p2057872.m2749.l2648&ssPageName=STRK%3AMEBIDX%3AIT But I think any other smart phone camera module will do this job. You will need to disassemble the complete camera module. The only part needed is the lens. The result was quite good. I could see a strong signal on the scope. (Between 2.5V and 3.5V while the red arrow is turning around) The complete design consists of the water meter sensor device, a box for the electronics and the electronics itself. Beneath the printed parts you will need two 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 the electric connections out of the sensor. Some heat shrink tube is also very useful. Building instructions Assembly Print all parts first. Put a M3 nut into the opening of the parts called SensorPhotoTransistor and SensorLED. Put these two parts into the water meter main part. Slide the rods through the holes of the main part and the parts with the nuts. Attach the knurled knobs to the rods. Slide some washers over the rods on the counter side and secure each of them with with a locking nut. The lens holder that slides into the part SensorPhotoTransistor Lens from a cheap smart phone camera module Disassemble the camera module. The whole lens system is a small disk 2.5 mm height, 4mm diameter. There is a lot of copper wire around the lens. It should be removed 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. Solder the 150 Ohm resistor to the LED, attach some wires and use heat shrink tube for electrical isolation. Solder the other end of the wires to the USB socket (See SV3 in the image) Do the same with the photo transistor. You must slide the photo transistor into the part SensorPhotoTransistor and the LED into the part SensorLED. Use some glue to fixate the parts. Glue the USB socket into the WaterMeterCap part. I used some sugru for it. Glue the WameterUSBCover onto the cap. 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 the electrical components. Move the photo transistor sled with one of the screws until it directly points to the tip of the desired arrow. Move the LED so that the white background is very well illuminated. You should use a multimeter or a scope to monitor the 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 the voltage increasing. Move the 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 that environmental light falls into the sensor. Additionally it helps to minimise fogging of the water meter cover glass. You may add some silica, too. If you have a good signal you are done. Attach a micro controller and evaluate the 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