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Topic: Potted plant watering system. (Involves water pumps.) (Read 26763 times) previous topic - next topic


I don't even have the RTC yet.

Alas I am having a real drama getting the solenoids.

Oh and I need a separate sensor for the main reserve of water, so if it is empty, the pump and solenoids are not turned on.

I don't see any requirement for a RTC here. All you need to do is water the plants every few hours - whether that is once in 24 hours, or once an hour, or whatever. The plants couldn't care less what time it is when they're watered.

For my system I am using a "Javtop JT-180 Solar/DC Water Pump" made in China and bought from an eBay retailer in HK for a couple of quid each including postage. It's tiny, draws almost no current, and works on anything from 3V to about 12V.

I suggest it's worth using a moisture sensor per plant, because the water requirements vary a lot with temperature/wind/humidity. Mine seems to work OK just measuring resistance between a couple of stainless cooking skewers pushed into the soil, although it took quite a lot of experimenting to find how to get a sensible reading from this design. I'm not sure the 'out of water' LED adds any value compared to just looking at the reservoir, but I am using an RF24 module to send the moisture and water delivery stats to a PC so I can generate an alarm if anything goes out of range - whether it's worth the hassle is for you to decide.


"That link doesn't work"
Here is the image with the important part.
Note: I said to use a 1 Megohm resistor. It's not critical, especially if using it as a switch.
10k would probably be more reliable, though less sensitive.


Well here are some pictures for those who may be interested.

It still isn't complete, but it is getting there.

But biggest problem right now is the power cables, de-coupling and the box into which it all goes.


More pictures.

The manifold has now had more work and it wired up.



Did some tests.  Loooking good.

The Arduino and other board together pull about 500ma - even with the relays operating.

The solenoids each pull about 700ma

The pump pulls 2A - well less, but to keep things workable.

I don't know if I should put a 7805 on the Arduino as while testing, a couple of the chips get hot.
Though the heat has to be disipated somewhere, I would prefere not on the Arduino.

Also will I need de-coupling?
Maybe a low ohm resistor and a cap to the electronics.....?

I shall get small caps for the solenoids and relays, and put a largish electro' cap on the supply, but would that be enough - without getting too complicated?


Have you only got one flyback diode for those four relays?


Yeah.  It is across the power rails.

The IC has flyback diodes on each circuit, but I may put another one on them.

As the whole thing only pulls 500ma with a relay operated, there isn't too much power pulled.


The IC has flyback diodes on each circuit, but I may put another one on them.

I'm not sure what the external diode is for, but as long as you have a flyback diode in parallel with each relay coil I guess you will be OK.


Well, way back......  although each coil has it's own "driver" (as in the + is switched) it was said to be a good idea to put a reversed diode to act as a general fly back for any other coils.

It would also be across the main + rail before the relay contacts to take any flyback from the solenoids...

Though that goesn't make sense either as the coils are AFTER the contacts.


yeah, thanks. 

Anyway, I am going to put .01u caps on the solenoids and relays as well.

Thoughts on the 7805 for the Arduino supply?


Well, way back......  although each coil has it's own "driver" (as in the + is switched) it was said to be a good idea to put a reversed diode to act as a general fly back for any other coils.

Now I'm unclear what you have got.

There should be a diode in parallel with each relay coil. This has nothing to do with other relays or solenoids - each coil needs a diode to absorb the 'flyback' energy that is released when you stop the current flowing through the coil. Coils have electrical inertia and when you switch them off the collapsing magnetic field tries to continue to pull current through the coil. This is the effect used to generate a high voltage spark in car electrical ignition systems. If you don't do anything about this then it will apply a negative voltage to your driver circuit to keep the current flowing, and this will dump extra heat into your drivers and potentially damage them through overheating or overvoltage. Any voltage spikes resulting from this can also upset the microcontroller. The diode in parallel with the coil provides a local short circuit that allows current to flow through the coil as soon as the coil voltage goes negative, so current can 'freewheel' through the coil and diode and gradually dissipate the flyback energy. Each coil must have its own flyback diode.

If the relay is switching an inductive load then it would be sensible to provide a similar flyback diode to absorb the energy when the load is switched off, but this would need to be in parallel with the switched load and not just connected between the rails.


I will try to bash up a schematic at some stage.

Alas finding a good program and time is not going to be easy.

No worries.

It may be a good idea because it will also help get ideas for the de-coupling which may/not be needed.


Here is a basic schematic.


The I/C which drives the relays have built in fly back diodes (as shown).

But that is where I am at.

I am asking now if I should need de-coupling between the relays and the electronics so noise doesn't get in.

I am also wondering if I should put a 7805 to power the Arduino.

I shall try to put .01u caps on the I/Cs where possible and maybe an electro near the electronics as well.


Here is the latest picture of the manifold.


New problem:

On the pictures of the manifold the plastic pipe overlaps the black pieces quite well and is "crimped" with cable ties.

The pump, however, is a different story.

The pieces of pipe protruding from the pump are a little bit shorter and narrower in diamater.

As I am still testing the system - and it does work! - the length of the pipe from the manifold to the pump is unknown, and the inlet piece of pipe is "work in progress".

The problem is this:
I bought a couple of those hose clamp things which wrap around a pipe and are tightened with a screwdriver.

All well and good, but the gap from the pump's body to where the first ...  "flange" thingy on the pipe is, is too narrow.  The clamp is wider than that.

No big deal, I just tighten it a bit harder than I would like.

I'm guessing that cable ties may be  the only ultimate way to go.  Are there any other tricks to help with this problem?

Thanks in advance.


Nov 25, 2012, 10:40 pm Last Edit: Nov 25, 2012, 10:42 pm by PeterH Reason: 1
In my experience screw clamps are great for larger hoses but problematic on very small diameters. Even with flanged fuel hose clamps I wouldn't expect to go below about 10mm.

If you want to seal a flexible hose onto a plastic spigot, then the three options I'd consider are:

  • Glue. If you can find anything that will bond with both materials, use this on it own on in combination with the clamping below

  • Small zip tie. The smallest cable ties I know of have a body about 6mm wide and would work as long as you have a spigot at least that long. I routinely use these for vacuum lines, small bore hoses used for windscreen washers and that sort of thing.

  • On shorter spigots you can just use several turns of wire twisted to tighten and lock it. I'd usually only consider this as a temporary fix, but for a low pressure system with only water in it, I don't see any reason not to use it as a permanent solution.

To have any hope of a reliable seal you'd need to support the hose so that the join was never under tension and was, if anything, under slight compression. Also note that the hose *must* be smaller diameter than the spigot so that it is slightly under tension. Trying to compress a hose down onto a spigot is asking for trouble.

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