Computer Controlled Irrigation System

The objective of this project is provide an automated irrigation system that keeps plants in our garden watered, whether we are at home or not. In the past we have lost many plants during the drier summer months, whilst on holiday. Suffolk is one of the driest parts of the UK.

Design

Design overview

To keep the costs reasonable, I've used off-the-shelf components for this design, available from most good garden centres. Tha main distribution pipes are standard hosepipe. The control will be achieved via an extension of my Home Control System (HCS), using an Ethernet IO board. This is so that I can fully automate the irrigation system and to avoid the need to have an additional controller. It will also enable remote control via my various interfaces, if required. The installation also supports manual over-ride, like all of the automation in my home.

In its simplest form, the irrigation will use computer controlled timers to deliver water to various pots and beds. Our Home Control System (HCS) is also aware of the external weather and the irrigation elements can adapt to it. The plan is to also add moisture level sensors to enable the water delivery to be more intelligent and efficient through feedback. Some feedback on water level is required to make sure the pumps doesn't operate with an empty water store.

One design consideration is that the control valves must be operated one at a time, to ensure the water pressure and flow remains consistent. As each valve is opened the pump is also switched on to raise the water pressure. As the on time it fairly short, this is not going to be an issue. The best time to irrigate is also after dusk, to minimise evaporation from the warm soli.

We have used stainless-steel jubilee clips to connect all hose pipes to the various connectors, vales and pumps. Typically these are 12-20mm size clips. Cheapest place I could find for these was eBay.

Water Store

Rather than connect an irrigation system to a mains water supply, we are assuming we can use harvested rain water. This is much more environmentally friendly and ensures no expensive water leaks can occur. The only downside to this approach is that this water supply is not under much pressure, though our water storage tanks are 1.5m above ground level and provide a decent head of water.

Water level sensor
The water store has a 'low water' sensor, which provides a signal back to the controller and stops the irrigation system running if the water store is nearly empty. This is achieved using a clear 25mm plastic pipe running up the side of the tank with a restriction at 50mm water depth. A small floating indicator with a magnet attached sits in this tube to give a visible indication of water level. Just above the restriction a reed switch is attached to the outside of the pipe. When the indicator drops down to the level of the restriction, the reed switch operates, signalling 'low water' level back to the Home Control System (HCS).

Because the water store is quite remote to the controller, this sensor is connected directly back to the Home Control System (HCS) I/O capability and doesn't route through the controller and to the enclosure. This also means the Home Control System (HCS) can report back the status of the water store and raise an alarm too.

Filter

ShurFlo inline water filter
To stop valves, pumps and the smaller distribution pipes and nozzles clogging up with debris, the main outlet from the store passes through a replaceable filter. We have used a ShurFlo inline filter designed for use in boats and caravans. It cost me about £10 on eBay. It also provides minimal resistance and a good flow.

Splitter

4-way splitter
To provide separate control to more than one irrigation zone, the water supply is passed through a 4-way splitter. The pipe leading to the splitter needs to be a decent size, to avoid restricting the flow. Normal hose pipe has worked fne fr us. The taps can be used to switch of individual zones if required and to also reduce the pressure going to each zone if required. This is another item I found very cheap on eBay.

Automated Valves & Pumps

For zones that only require a drip feed of water a simple controller valve can be used to turn the water on and off and the head of water in the store provides enough pressure for the drip feeds to work.

Pump

The advantage of using an inline pump is that they can be situated next to the controller and below the water level, to ensure they are self primed. One issue with using pumps is that they are not a closed pump and the head of water in the store causes them to run through them, when they are switched off. The plan is to fit an actuated valve in line to control flow through each delivery channel.

Whale GP1392 inline water pump
I'm using a pump is required to increase the water pressure. For the initial testing, we are using a 12V in-line pump, which can pump 12 litres per minute. A power feed is taken from the input to each valve (via a diode), to drive the pump when each valve is switched open.

This pump is surprising powerful and can pump against quite a high static pressure. Ideal for this application.

12V inline valve
These are the 12V diaphragm valves I'm using in this project. I bought them from Virtual Village. These valves are not designed for gravity fed systems but the pump ensures they operate as expected. There is no obvious polarisation to the input as far as I can see. Maybe I just got lucky!

Controller

For testing purposes and to allow manual control, we have added single pole, double throw (on-off-on) switches (Maplin part no. JK28F) inside the enclosure. These means we set the zones to on, off or auto.

The enclosue is linked to the Home Control System (HCS) I/O board using a 7-way cable and a 7-way DIN plugs/socket. The Ethernet output board lives is in our garage. The pins are:

  1. Zone 1
  2. Zone 2
  3. Zone 3
  4. Zone 4
  5. +12V
  6. 0V
  7. Soil humidity feedback (+12V = dry)

Because the controller is essentially part of our Home Control System (HCS), we can fully control the operation of each zone. The zones can also be manually controlled via our iPhone/iPod web app but, this is more for gimmick factor than being a useful thing to do!

12V Drivers

The controller needs to switch 12V power at fairly high current. To achieve this we have used a relay output board to switch the 12V power to the valves and pump.

12V Power

Our irrigation system is actually powered by a 12V solar charged battery bank in our shed. All of the garden-side elements are fed through a 12V regulator though, since the humidity sensor needs a regulated supply. The whole system is optically isolated from our .

Soil Humidity Sensor

One thing we quickly realised is that there is no point in watering the plants if it is raining outside. In an ideal world, you would have a soil humidity sensor in each zone providing feedback on a zone by zone basis. This will then enable optimum use of the water in the store but, this is overkill for our situation.

Soil humidity sensor
To achieve this function we have a single Maplin module connected back to the enclosure and reporting back soil humidity status as a binary signal to the Home Control System (HCS). Note that this requires a 12V DC [UR] (regulated) power supply. This module is made by Kemo.

This module can work in two modes since it has been designed to directly control an irrigation system in isolation. The first involves a delay timer to test the soil moisture levels and activate the water delivery. The second (test mode) provides an instant and constant feedback on soil humidity and we have used the sensor in this mode.

Soil humidity sensor probe
The sensor probe is attached via a length of wire to the sensor electronics. We use a single soil humidty sensor and this probe sits outside the zones and reports back the general moisture content in our garden soil. This means we can determine if it has been raining recently and not activate the zones.

Delivery

4mm T-piece
We are also planning to 4mm t-pieces within individual pots and tubs to enable water to be distributed better.

180° mister
This 4mm Hozelock 'Micro Irrigation' (part no. 2722) attachment provides a 180° fine mist spray with a claimed radius of 1.0m. They come is packs of 6 and cost about £3.70 per pack. These fittings have provided the best results so far. They can be fitted into a normal piece of hose by drilling a 2mm hole in my hose pipe and simply screwing them in. Each zone can easily supply six of these to the claimed 1.0m reach and beyond. We have used the taps on the splitter to lower the pressure.

360° spray
This 4mm attachment provides a 360° spray. To be honest, these have not worked well for us. They seem to need a very high pressure to work effectively.

Progress

Water Pressure

Initial testing has shown that the existing head of water can drive water out of approximately six of the 180° mist sprayers but, it can't drive water out of the 360° sprays. This has led us to re-think my design and to use one single pump to drive all of the delivery channels.

Having tested with the pump in place, the water pressure is now a bit too high for the 180° mist sprayers but we can use the taps on the splitters to restrict the flow slightly.

Enclosure

All of the main elements are now mounted in a enclosure, ready to install in the garden. The 'water-side' components are mounted in a separate box to the electronics, to ensure they are kept dry. The enclosure is made out of wood, to blend in with the surroundings and features a lift up sloping lid, which allows us to lift out the boards holding the main components.

All of the inlets and outlets are connected via push-fit connectors, which means the enclosure can be removed easily. These connectors are a little bit susceptible to leaks but all have have new seals and washers. These connectors are amazingly cheap when bought from supermarkets and similar stores.

Enclosure open
Enclosure with front rtemoved to show splitter and valves. The pipework above the pump allows me to vent out any air. Above that you can see the four switches mounted on the rear panel for manual over-ride.

Pipes & Distribution

From the main enclosure, we have installed ducting around the perimeter of my garden, in which the hosepipes can run underground and out of sight. So far we've fully installed zone 1, which covers the herb garden and vegetable plot. Where the hosepipes have surfaced, we have mounted them using 15mm pipe clipes. These hold the hosepipe nice and tight (to stop it rotating) and allow us to insert the misters and microbore pipes off to the other distribution components.

This is zone 1 in action, a small vegetable plot.

Further Reading

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