Cats LOVE running water. It 's their instinct to drink running water because it's much more likely to be fresh than water that's standing still. So, drinking from a normal bowl does not really encourage them to drink. And drinking is important for their health. Our cat was constantly asking for opening the tap, which caused of course a lot of spilling water. This brought me to the idea of constructing a little fountain for the cat with a micropump and filter. The additional benefit, besides cats being more interested and drinking more is that the water is constantly flitered and aired for better water quality. Later I found out that these fountains are actually already commercial available, but it is fun and educational to make one yourself. Besides, I want a ceramic bowl not a plastic and this was expensive or not easy to get with the commercial models. Reviews say a ceramic or stainles steel bowl is better than plastic for the water quality. Furthermore, I want absolute garantee the fountain is QUIET. And this is what the electronic circuit in this project is about. We're going to tune the pump down below its nominal operating level, making it absolutely quiet and very efficient in consuming electric power. The cats don't need a lot of water running, even dripping water makes them interested. A stream too aggressive can even make them scared. That's not the result wanted. First, I ordered a DC brushless micropump from eBay. Brushless, for a long lifetime. It was the smallest model (and cheapest ~ 8 euro) I could find: a JT-180A, made in China. You can find it in many shops on eBay. In itself this little pump is already very effective with power. It's operating voltage range is from 3.5 to 12V. At 12Volts this little pump shows quite a lot of power! It is specified it can pump water up to 2 meters high, or pump 360 liters/hour. However, I am interested in the LOW end qualitifications of the pump. I found that, at 3.5 volts the pump is not garanteed to start. sometimes it starts only at 5 volt and sometimes even 7 volts is needed. At 5 volts the flow of water is already too strong. Even when you tune down to 3.5volts it is still quite strong. (I had 10 cm tube connected to the pump when experimenting.) Then, it was possible to tune down the voltage to 1.8volts with the pump still running, a very small stream: no noise at all, perfect for the Cat-Fountain. Thus, in short, the pump needs a hig voltage to start, but can keep running at 1.8volts. Now, if you see the picture of the pump you will see that it has, apart from the black and red wire for powering it, a third white wire. I didn't know what this wire was for and I couldn't find any information on it. Last month there was an article in Elector with a brushless motor in it with three wires (model ariplane), but there was no explanation in the article about the third wire's function. My first guess was right: it gives feedback about the rotational speed. I connected the white wire to my oscilloscope and had the pulses on screen. The low speed when the input was 1,8volts gave a pulse frequency of 30 Hz. At 12volts the frequency is around 110Hz. You could lower the water flow by abstructing it's flow (through a thin pipe for example) but that not's efficient and makes the pump more noisy. Now the white wire that gives frequency feedback will make the circuit shameless simple: what came quickly to my mind was a little PLL circuit with the old but versatile cd/hef 4046. The micropump will here be in the role of the vco and the oscilator of the 4046 will be used as the input oscilator where the pump will be tuned to. It is also practical that the 4000 series operate from 3 to 15 volts, so the circuit can run from 12volts dc directly. By varying the oscilator of the 4046 with a potentiometer, the waterflow is variable as an extra. I will soon be back with the results after circuiting the circuit.
Update: the result is that I got wet and so far the fountain was untameble. I thought it was going to be easy but I cannot put more time in it (many other things to do). For the cats I'm just make a classic potentiometer adjustable switching power supply. Don't worry, they get their fountain.