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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? http://denkovi.com/product/13/16-relay-board-for-your-pic-avr-project-5v.html or do I need a chip to actually talk to the board.
2. 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?
3. 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?

Brandon
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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? http://denkovi.com/product/13/16-relay-board-for-your-pic-avr-project-5v.html 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.
http://arduino.cc/playground/uploads/Learning/solenoid_driver.pdf



2. 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.

3. 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


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wow, looking at the prices, I could find the 1n4004 for a penny. however I can't find the tip102.  Is there anything on the following link that could take it's place?
http://www.taydaelectronics.com/servlet/the-%28-T-%29-Transistors-cln-TIP-Series/Categories
Or do you have a suggestion of a company that sells all the pieces needed?

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wow, looking at the prices, I could find the 1n4004 for a penny. however I can't find the tip102.  Is there anything on the following link that could take it's place?
http://www.taydaelectronics.com/servlet/the-%28-T-%29-Transistors-cln-TIP-Series/Categories
Or do you have a suggestion of a company that sells all the pieces needed?



I'm pretty sure ANY of the NPN transistors listed on the page would work fine. In your use, the transistor is just being used as a on/off switch. So as long as it's voltage and current ratings are well above what your circuit requires, you are golden. I think this one probably matches closest to the TIP102: http://www.taydaelectronics.com/servlet/the-72/TIP122-Transistor-Complementary-NPN/Detail

Lefty
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One last thing: I was looking for the resistors shown in the schematic.  I noticed that the resistor is rated 1k or 2.2k, however it appears that when I lookup resistors to purchase they come in 1k @ 1/4w, 1k @ 1w.  Some are metal film, some are carbon film..  What should I purchase? does the wattage and the film type matter?
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One last thing: I was looking for the resistors shown in the schematic.  I noticed that the resistor is rated 1k or 2.2k, however it appears that when I lookup resistors to purchase they come in 1k @ 1/4w, 1k @ 1w.  Some are metal film, some are carbon film..  What should I purchase? does the wattage and the film type matter?


Do you know Ohm's law?

P=IE

P = Power, measured in Watts (can also be VoltAmps)
I = Current, measured in Amperes or Amps
E = Voltage, measured in... erm... Volts... can't remember what the E stands for, it's one of the three different phrases that means Voltage..

So basically if you have a circuit with 5 Volts (the max voltage of the Arduino) you can have up to 200 milliamps with the 1W resister, or 50 milliamps with the 1/4 W
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One last thing: I was looking for the resistors shown in the schematic.  I noticed that the resistor is rated 1k or 2.2k, however it appears that when I lookup resistors to purchase they come in 1k @ 1/4w, 1k @ 1w.  Some are metal film, some are carbon film..  What should I purchase? does the wattage and the film type matter?


It's very non-critical in value. It sets the base current value when turning on the transistor. Becaused of the very high current gain of that darlington transistor, it will saturate the transistor with either a 1k or 2.2k resistor. Any wattage rating you find will be more then enough running at the arduino ouput pin voltage of 5vdc. Carbon, metal film, they all will work fine in this simple switching application. Buy what's cheapest.

Lefty

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I sell an Arduino shield that does more or less exactly what you want. Sixteen high current DC outputs per shield, and it's designed to be daisy chained in groups of up to 25, for 400 outputs. http://www.logos-electro.com/ard-srg-ips4x4-1/. It will handle the voltage and current of the valve you linked with no problems at all.
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Quote
the goal of being able to turn these devices on and off very fast.
How fast are we talking about here.
The problem with rapid switching of inductive loads is the time it takes for the current to rise in the coils. This is self limiting and the way round it is to use a higher voltage but then chop regulate it so the current stays within the limits. There is also a limit on how fast the solenoid will move given the mass, inertia, and applied magnetic force.
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I want to be able to turn the valves on and off within a tenth of a second at times. Maybe I need to go with 120V valves and relays instead?
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That is not going to be a problem at all. By electronics and most solenoid standards, a tenth of a second is an eternity.
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While 100mS is a long time in electronics terms in mechanical terms it is quite fast.
Most solenoids are only powered in one direction and rely on something like a spring to do the return. I would say turning on and off this sort of mechanical arrangement in 100mS is about it's limit.
There are other sorts that are like a push me - pull you that could respond at this speed. 
You need to sort out exactly what solenoid you are going to use.
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High speed is part of the point of solenoid valves. smiley

Normally-closed direct-acting solenoids, which is what the linked valve appears to be, tend to have response times in the 10-20 ms range, in both directions. Some may be faster -- Snap-Tite's small valves are around 5-10 ms, and I've seen 1 ms for some wickedly expensive aerospace stuff. These types of valves are *NOT* spring-closed -- they are closed by the pressure of the upstream fluid. The spring is there to keep the parts correctly aligned and keep the valve closed in the absence of fluid, so that no leakage occurs when fluid is introduced. Even piloted valves in this size range are faster than 100 ms, assuming sufficient upstream fluid pressure is available to operate them correctly. However, since the data plate on the top of the linked valve indicates it will operate from 0 pressure, it's direct-acting, not piloted.
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