Arduino, Processing and water pumps

[benonez]

 I am running a sketch in Processing 2.0 that sends MIDI out. The MIDI drives my patch in Ableton Live. It sends three control change per "frame" (this is Processing I’m talking about, so the action in my code occurs in the draw() loop, so 30 times a second the program spits out this MIDI info). So, I just want to mention that I’m not running the Arduino.ino, and want to use Processing’s Serial library to communicate with the Arduino.
OK, this is where you come in:

For my project I need to control the speed of three water pumps with the Processing sketch. I think I’m going with 120V AC pumps like this one:

http://www.ebay.com/itm/210-GPH-Submersible-Pump-Aquarium-Fish-Tank-Powerhead-Fountain-Water-Hydroponic-/251400348354?pt=LH_DefaultDomain_0&hash=item3a88a0e2c2

One solution I thought might work was to pulse a digital out pin on the Arduino and connect that to a SSR connected to the pump but I also see tutorials on using the Arduino program with a triad and an optocoupler circuit.

That’s the gist of my problem. My first question is:

Is there a solution where I can just use Processing?
Also, any ideas on pumps would be appreciated.

Thank you,
Ben

[retrolefty]

That pump product page doesn't mention the voltage and current requirements for that pump? If AC then applying variable speed via an arduino has lots of possible problems. Even with a phase controlled SSR (as used in light dimmers) often have problem when used with inductive loads like motors. A DC motor would be a lot easier to control with an arduino via a logic level power mosfet for either just on/off control or variable speed via PWM output.

[benonez]

I bought this one:

http://www.ebay.com/itm/Ultra-Quiet-Mini-DC-12V-3M-240L-H-Brushless-Motor-Submersible-Water-Pump-Hot-/261351083541?pt=LH_DefaultDomain_0&hash=item3cd9bd0e15

and a motor shield:

http://www.ebay.com/itm/Motor-Drive-Expansion-Shield-Board-Module-L293D-For-Arduino-Duemilanove-Mega-UNO-/181404832434?pt=LH_DefaultDomain_0&hash=item2a3c9212b2

However, I couldn't vary the speed using the Ardiono program. That tiny pump might be powerful enough for my purposes, so I'd like to try and get it to work.

[xuio]

The pump you bought has a brushless motor in it, brushless motors (BLDC) can not simply be driven off a DC voltage.
They have 3 phases and need some sort of controller to run, the controller is driven by the input voltage, so if you try to regulate the pump with PWM, the controller has not enough time to power on, and the motor wont run.
You could try very slow PWM (1-2Hz) or use a pump with a controller that has a speed control or (if you find any) use a brushed DC motor pump.

[Paul Moir]

Throttling the pump may make more sense with a valve attached to a servo.  It might mean you would only need one pump?  Or if you didn't have to change speeds fast and have space, you can use an accumulator and pulse the pump every few seconds - like a 15 second PWM.  (Think of a domestic water supply system.)

However, I *know* I've seen windshield washer pumps that were brushed DC motors.  They're not designed for continuous duty but I don't know if longevity is important in your design.  Those you can PWM.

[benonez]

Thank you all for your informative replies. One question I have is can I use a digital potentiometer (as I have some lying around) to control the cool side of a dimer circuit?

[Paul Moir]

Most dimmers don't have a "cool" or isolated side, so no.  The way to interface with one is to use an optocoupler.  The easiest/dumbest is to use an LED paired with a CdS cell because in the classic TRIAC/DIAC dimmer circuit the voltage across the pot alternates.  You PWM the brightness of your LED with your Arduino and replace the pot in the dimmer with the CdS cell.

Once CdS cell optocouplers were fairly common, but the restrictions on Cd seem to have put an end to that.  Plus you can design around them and use phototransistor optocouplers which are cheaper anyway. 

EDIT:  There are photoFET optocouplers which can be used for AC, but only for very low voltages.