Year 8 - Moisture Tester Project

In this page you will find all the information you need to complete the moisture tester project.

The circuit

  • In this section the components are soldered onto the pre-drilled PCB board.

  • The photo to the left shows the part of the circuit which goes into the soil, and where all the components are soldered into.

  • This side of the board has tracks of wire etched on to it and they conduct the current around the circuit.

  • In the photos below you can see the circuit at various stages of manufacture. 

  • In order to make the battery clip more secure in the PCB a 1.5mm hole is drilled and the red and black wires are fed through and soldered.  The reason for drilling these holes is so that the battery clip is more secure and should not pull out as easily.  The wires will pull out if you have a battery plugged into the clip and it is hanging as you carry the circuit around the room, so be careful and do not let this happen.

  • When you are making this project all the components are located in one box. When all the components are soldered onto the PCB the extra leads need to be cut off, as you can see from the photograph these leads are not needed and can be dangerous and are sharp.


How does the circuit work?

When the circuit is inserted into the soil it will detect if there is any moisture in the soil by turning on the LED (Light Emitting Diode). If the LED does not come on then there is no moisture in the soil and you need to water your plants.

Circuit components





Tools required to build a circuit


















Making the housing


In this section several pieces of equipment were used:

Vacuum Forming:

  • The Vacuum former was used to create the main part of the housing.

  • There was a wooden mould placed into the machine and lowered.

  • A plastic sheet was secured above the mould and the heating element turned on.

  • The plastic was allowed to heat for approximately 1 minute.

  • The moulds were then brought up to the plastic and the vacuum pump was turned on, this allowed the air to be sucked out between the plastic and the mould, thus forming the required shape.

Using the Gerbil:

  • The Gerbil was then used to cut out the plastic mould.

  • To use the Gerbil you need to wear goggles/face protector and make sure that your hands are well away from the rotating blade.

  • As you can see from the picture the blade comes through the surface of the plastic and is potentially dangerous if not used correctly.

The Moulds:

  • In order to Vacuum Form properly a good mould is essential.

  • In class you had the choice of three moulds.

  • These moulds are made from hard wood or plywood or a mixture of both, which is essential if the mould is to survive a large number of mouldings.

  • The hardwood will allow the mould to give a lot of details and you can see that detail in all three moulds.

Assembling the moisture tester

To assemble the moisture tester together:

  • The edges of the vacuum formed plastic were cleaned with sand paper to remove any excess material. 

  • A slot was cut out of the vacuum formed piece for the circuit. 

  • Both pieces of vacuum formed plastic are put together and a hole is created using a "punch" or the "cordless drill."

  • The circuit is then put in place and the housing is held together by either screws or paper fasteners. 

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