The timer electronics controls a small electric motor which turns a ball valve to let water flow. The motor turns clockwise (with normal power polarity, ie +ve to red), and the ball valve is fully open just before the cam driven micro-switch is triggered and closes the NO (normally open) contacts. As the motor continues to turn, the ball valve slowly closes, and is fully closed when the cam releases the micro-switch (so it goes open-circuit, back to NO condition).

As the motor is driven in one direction only (ie doesn't have to reverse to close the valve), it makes driving it slightly simpler - it just needs a single transistor instead of an H-bridge driver.

The motor is geared down by a series of 6 reduction gears. The motor has 14 teeth, the gears have 40/14, so a reduction of approx 544:1. So if the motor does something like 6000 RPM then it would take about 3 seconds to do one cycle from on to off (half a revolution of the ball valve).

This example is damaged, the LCD has broken down (water leakage?) and the battery cover, and front cover are missing.

The whole thing is held together via four screws hidden under the front panel label. The label can be pealed off to reveal the screws, but that label contains a flexible printed circuit for the front panel keypad which can be easily damaged.

• GardenMate user manual.
• Groundwork Automatic Water Timer photo.

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