Dancing Water Fountain

[ivanabela]

Hi,

I am working on a water feature for my garden which shoots 5 water jets from the ground. Basically the setup consists of a pump which feeds a 1" pipe to which the 5 outlets are connected. At every outlet there is a 12v solenoid valve which draws 250mA each.
Every solenoid is independently controlled so as to have the "dancing" effect.

To test the setup I wired all 5 solenoid to a 5 gang switch (to switch every solenoid on/off independently). Everything worked according to plan, so now i'm into the next phase of the project, ie. make a picaxe based controller which will switch the solenoids at random or in sync to get the dancing effect or something similar.

In your opinion, which would be the best way to do this? Which components would you use? FETs, Relays.....?
I didn't start yet so I am all open for any suggestions. Anything will be considered at this stage.

Thanks

 

[Dicky Mint]

Hi and welcome. For your circuit I'd use BUZ11s to turn the solenoids on and off as they will probably cope with the 12 volts switching voltage being above their gate voltage, around 5V, for PICAXE. I'd drive their gates direct via a 1k0 resistor from an output pin on a PICAXE. The BUZ11 is overkill but it will easily cope with the voltages and currents involved. The program would be the fun bit but hopefully no too daunting a proposition. Good luck

 

[premelec]

Inductive transient suppression

Be sure to use back diodes across the solenoid coils which will have an inductive kick back transient when switched off - by switch or MOSFET - these transients can cause the FET to fail and various other problems. If you instead use a darlington driver such as the ULN2803 it has the diodes built into the IC.Happy dancing fountain!

 

[geoff07]

Some inspiration: http://www.youtube.com/watch?v=mQOH4LmQd9U

This one in Bandar (capital of Brunei, north coast of Borneo) is about the size of a football pitch. Built by Jefri, brother of the Sultan, in a theme park, and cost unimaginable amounts by all accounts.

 

[John West]

Looks wet.

___

Avoid using relays to drive the solenoids. Darlington's or MOSFET's are the way to go, particularly for low to medium power DC toggling. Solid-state devices will last much longer than relays.

As you say the solenoids are 12V I'd probably use the MOSFET's, as good cheap ones will drop less voltage than the Darlington transistors. But either will work and the Darlington array is compact and cheap.

No matter what type of switching device I use I always put a reverse polarized diode right across the solenoid terminals. They're cheap, and that's the best place for them in order to fully suppress the back-EMF as well as reduce the possibility of nuisance RF pulse noise radiation. When working with a string of solenoids and a PICAXE, it's always a good idea to well filter the solenoid inductors, as well as well filter with capacitors the micro-controller and power supply, and keep the grounds for micro and solenoid separate all the way back to the power source.

 

[techElder]

ivanabela, come up with some sort of "language" to describe your show. Maybe even a mini-interpreter. It will make changing your water program so much easier.

 

[SAborn]

I have seen something similar set into a pavement near the beach, which used light or touch sensors around the water jets, on normal operation its just a random patten, but kids get facinated by it and stick their foot over the jets, which then the patten changes and the water pops up on a different jet, they then stomp on that one and the water moves to another jet and so on.

It keeps the little buggers busy for ages trying to beat the patten. (which they never do)

Its like a cat and mouse game.

Depending on your set up you could do similar with using touch sensors, as from my testing water dont effect the touch sensors very much.

 

[Dippy]

I agree with the MOSFET low-side switch plus back-emf diode across solenoid approach.

In addition, when you have reactive loads like that, there a couple of extra good additions.
1. Decoupling caps right next to PICAXE on power pins. E.g. a 47nF ceramic and 47uF/>10V paralleled.
These will reduce transients and noise upsetting PICAXE. Most designers use decoupling as 'standard issue'.
and
2. On each solenoid site; a 220uF / suitable voltage cap. The +ve leg on the +ve leg of solenoid, the -ve leg on Ground.
This will reduce the transient switch-on and switch-off transient surge getting back through the power line. AND it it can help with switch-on performance if wiring or PSU is weedy. This is often used with relays too.
3. Optional: A few nF between 'reset' pin and Gnd. Microchip recommend this is many apps.

 

[KMoffett]

Hi and welcome. For your circuit I'd use BUZ11s to turn the solenoids on and off as they will probably cope with the 12 volts switching voltage being above their gate voltage, around 5V, for PICAXE. I'd drive their gates direct via a 1k0 resistor from an output pin on a PICAXE. The BUZ11 is overkill but it will easily cope with the voltages and currents involved. The program would be the fun bit but hopefully no too daunting a proposition. Good luck

BUZZ11's Vgs(th) is as high as 4V. That's the voltage that the MOSFET just starts to turn-on. For saturation you need ~10Vgs. I would recommend a logic-level MOSFET if you are going to drive then directly from a PICAXE.

Ken

 

[techElder]

ivanabela, something else I thought of. After visiting Disney World's version of the dancing squirters, I realized while sitting and watching that you don't hear anything but the water.

So, put your solenoid valves in a remote location where you won't hear them pulling in. That might take some doing, because the extra piping will create a "resistance" in the stream after the solenoid. You might need to adjust your incoming pressure to allow for this.

You'll want to get the solenoids (and other electrical wiring) away from the wet areas anyway.

PS. Water in a piping circuit acts very much like current flow in an electric circuit.