Hi there,
What I'm trying to do is to randomly power 2 aquarium power heads which are basically 120 vac water pumps. The idea here is to re-create the wave motion seen in the ocean. So I'm looking for a random timer connected to relays. Time sequence from 30 secs to 3 mins or so. Any thoughts?

 

I always think microcontrollers, are you open to this ( say Arduino )

 

Gimme what you got

 

I don't like the idea of driving 120v pumps from a microcontroller, particularly considering that its likely the project involves a saltwater tank. 120VAC + saltwater = shock hazard.

There also may be a hazard to the marine life in the aquariums.

It would be more safe to use a low voltage pump, or something like an automotive windshield wiper motor that displaces water in the top of the tank to create a wave action; something like a large piece of PVC pipe (maybe 6" diameter) with it's ends sealed, or a large ball. The speed of the motor would change the frequency of the waves.

At some point, it's likely that you will find a resonant "slosh" frequency for the tank(s) in question. If operated for a period of time at that frequency (or a harmonic of that frequency), you could wind up with water sloshing out of the tank(s).

 

There should be no problem driving from a microcontroller if you take precautions. These might include a relay or optical isolator. Do not assume that the microcontroller lines will not become hot, put it in an insulated or grounded box.

That said.

Take say an Arduino. It has a bunch of 0 - 5 v digital outputs for you pumps or whatever.

There are libraries for generating random number, use these for controlling the outputs.

If you want put some sort of "large wave detector" in the aquarium then you can dial back the pumps if the waves are too large.

If this approach seems useful there are tons and tons and....... of links on the Arduino from Google.

 

I doubt that your idea of turning a pump off/on will get your desired results.

We had a setup with a 10ft x 100ft pool, where we 'bobbed' a float, run by a reciprocating motor, that worked very well. For smaller surfaces, you could run the pump discharge into a rotating cylinder that had one side open. The effect is releasing a quantity of water at controllable cycles.

 

wouldn't it be better to drive a small geared motor with a paddle in a box to create the waves?

A windscreen wiper would be perfect as it's aleady geared and it designed to work in an oscillating movement.

 

The "Wave" action I'm looking for is not surface wave action. In reef tanks, random water flow is ideal for corals and fish; the incoming and outgoing of the water column for example. I've never experimented with microcontrollers before. They sound very interesting and I could see using one to control a couple of optical isolators to trip relays that supply 120 vac to my power heads. I've been out of the engineering loop since college and I'm know the technology has changed. If you all could steer me to some web sites I would appreciate it or if you have some schematics you could share. You all have been really helpful...

 

'Net sure of pump sequencing, how long ON, & how long between cycles, so threw up a straw man to throw kneves at. Pump random ON time ckt. uses a free-running 555 oscillator, continuousling cycling a 4017, 0 thru 9, with outputs connected to different timing resistors, giving 3 sec. incrimemts. The leading edge of a trigger pulse[ inverter got lost], sets one-shot C , pin 3 hi disables B via clock enable,p 13, 4017. C will output a 3 to 30 sec. pulse, depending where B stopped. C controls a solid state relay to turn on pump. The trigger comes from a second random pulse gen. using A & new B' & C', with maybe different timming. Maybe a start at least.

 

how about one of those slow output AC motors (typically found on humidifier drums) to oscillate your output tube?

 

Well I've been looking at the Arduino website and never even knew these little doo-dads were out there. Very cool. I'm sure a lot of you folks have used these microcontrollers. Are they robust enough to be on 24/7?

 

I don't know about Arduinos, but I've had a little PIC12F675 sitting here on my desk flashing a dozen LEDs for a couple of years, 24/7.

Trane air conditioner compressor control panels use a PIC16 uC. My folks' place in Florida has had that A/C running 24/7 for 14 years in temps ranging from freezing to 100+ degrees under very humid conditions.

It's still running.

 

Well I'm on a mission on developing some low cost aquarium products. I've been a "reefkeeper" for over 20 years and I'm amazed just how expensive some equipment is. I KNOW that something like a lighting hood utilizing a LED arrays does not cost $4000-$5000 to build and is marked up beyond comprehension!!! I guess it's time to do some research into these chips and learn how to use some of them. May I ask, are you an engineer in the electronics field?

 

The arduino is a solid little system. As reliable as anything you are likely to build.