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I am asked to implement a small indoor musical fountain which consist of around 45+ solenoid valves.

Rather than having separate dedicated lines to the valves, I would like to implement something like how addressable LEDs works, so that we can send a signal from Arduino exact same way the Neo Pixel LEDs works, the corresponding valve has to toggle its state.

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I think that is better than daisy chaining shift registers like 74HC595.

How can I achieve that? I have no idea how the addressable LED actually works. Guess it is some sort of PWM way.

Please suggest some sort of address reading system that can connect to each valve and can toggle the valve.

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    \$\begingroup\$ The average water valve tends to be 24V AC. You also need to consider the combined current of 45+ solenoids. Running separate wires solves some of the problems. For switching the solenoids, relays would probably the simplest/cheapest option as you can easily purchase relay boards for the Arduino. \$\endgroup\$ Commented Dec 8, 2020 at 10:40

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Should the solenoid valves have DC coils, this 7 x 7 matrix could be used.

Only 14 relays would be required.

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Addressable LED strips work like shift registers, more or less; the data for each RGB value for each LED is clocked into the string of LEDs serially, and every integrated LED controller IC (one for each LED) passes on RGB values to the next one. See How does an addressable LED in a strip work? for more explanation.

You can buy the LED controller chips (like the WS2801) separately, but using those for your application would just complicate matters compared to simply using shift registers, and you would need a lot of them.

Another way of implementing what you want is using a few I2C-connected I/O-port expanders, like, for example, the PCF8574 or the MCP23017 (there are others). You can set their address with three bits, so you can have 8 of those on one I2C bus.

You will, of course, also need relays (or another way of switching), and a way to drive them from the IO lines.

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For one-off setups like this, the simpler is usually the better. Use addressable LEDs, and take their light output to control the valves. A phototransistor illuminated by the LED, driving a mosfet as a switch, will do the job with plenty of speed for a fountain application. You could put the whole thing together as a prototype in an afternoon or two. Make sure the valve drivers are in small opaque plastic boxes so that external light doesn’t trigger the phototransistor. The LEDs don’t have to be driven very bright either.

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