Interface arduino up to 50 solenoids?

Using Arduino Motors, Mechanics, Power and CNC
2

metrix:
I am a programmer interested in interfacing a computer to the outside world, but I need a little information on the electrical side of things. At some point I will want to work with 50 of these solenoid valves: "http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=400190081934&ssPageName=ADME:X:eRTM:AU:1123" but at first will only connect 8 devices with the goal of being able to turn these devices on and off very fast.

  1. Can I interface an Arduino to a board like this? Relay module 5V - 16 channels for Raspberry PI, Arduino,PIC,AVR or do I need a chip to actually talk to the board.

Yes you can wire arduino digital output pins directly to the input channels of that relay. How ever that method won't scale up to 50 output valves you may want without further added circuitry or upgrading to a mega board. You will also need to have the ground connection of the relay board also wired to a arduino ground pin. You have to supply the relay board with a source of +5vdc to power the 16 relay coils and looks like it requires around 2 amps of +5vdc power capacity, too much to power the relay board from the arduino's +5vdc pin. You also of course will require a rather large +12vdc power supply to handle the 8, 16, or 50 12vdc water solenoid valves you are controlling. Your looking at a 9amp +12vdc supply if you want to design for worst case of 50 valves turned on at the same time.

However if you can built circuits yourself, you can save a lot of money by just using switching transistors to switch the water valves directly instead of using the added relays used in that relay board. Here is a typical wiring diagram showing how a arduino output pin can control a DC solenoid.
Arduino Playground - HomePage

  1. From my initial research it looks like inductive loads can be a problem, what circuitry would I need to add to the board above to handle an inductive load? Is there a relay board that has the circuitry built in to handle deal with inductive loads?

On the relay board link, notice the sample schematic of a single channel relay. It has a 1N4007 wired in reverse polarity across the coil terminals, that will deal with the inductive kickback when the coil is de-energized. Also the arduino link showing a single solenoid interface circuit also shows a diode used for the same purpose. That should handle the inductive load situation in either case used.

  1. At first I want to work with 5 or 6 solenoids, but as I get more comfortable with these devices I will want to scale up to around 50 or maybe even 100 relays. Would I be able to do this on an Arduino board? Would I be better off getting 8 channel USB boards and interfacing them to an old computer?

There are Arduino shield add-on boards that can be used to obtain additional output pins. Also the Arduino mega board comes with 54 I/O pins and would be the simplest approach.

Lefty