Moisture Tester | clounaghtechnology

Year 8 - Moisture Tester Project

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

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

PCB Circuit This is the circuit before any components are added to it.	Circuit with components in place The components have now been put into position.	Components Box This is the component box. Here you will find everything you need to build your circuit.
The Soldered Circuit This photo shows the circuit with all the components soldered in position. Now the excess wires need to be removed.

Transistor Transistors can be regarded as a type of switch, as can many electronic components. They are used in a variety of circuits and you will find that it is rare that a circuit built in a school Technology Department does not contain at least one transistor. A Transistor has three legs these are called a base, emitter and collector. It is important that they are put in the correct position in the circuit.	LED (Light Emitting Diode) LEDs produce red, green, yellow, or orange light. LEDs are part of the diode family. The LED has one long leg and a short one. The long leg is POSITIVE and the short leg is NEGATIVE. It is important that the LED is connected the correct way otherwise current will not be able to flow through the component and it will not work.	Component Display Boards This is a display board explaining LEDs and Transistors. These boards located in are in each of the Technology workshops.
Resistor Resistors determine the flow of current in an electrical circuit. Where there is high resistance then the flow of current is small, where the resistance is low the flow of current is large. Resistance, voltage and current are connected in an electrical circuit by Ohm’s Law.	Resistor Colour Code Chart Resistors are too small to have numbers printed on them and so they are marked with a colour of coloured bands. Each colour stands for a number. Three colour bands shows the resistors value in ohms and the fourth shows tolerance. We can calculate the value of a resistor using this chart.

Soldering Iron This is a soldering iron. It is used to melt solder wire and help make an electrical connection within a circuit. (You can read more about soldering by clicking the button below.)	Wire Strippers Wire strippers are used to remove the plastic coating and expose the metal wire so it can be soldered to components/circuits.	Long Nose Pliers These pliers are used for both cutting and gripping wires. Their namesake long gripping nose provides excellent control and reach for fine work in small or crowded electrical enclosures.
Side Cutters These pliers are used to cut the wire to the correct length.

Read More about Soldering

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.

Vacuum Former	Vacuum Formed Plastic	Moulds Loaded into Vacuum Former
Moulds	Gerbil Cutter	Gerbil cutting out moulded plastic

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.

The Moisture Tester This picture shows the completed moisture tester. The LED is located on the body of the ladybird and the circuit is held inside the housing.	Drilling a Hole in Plastic For the ladybird mould a hole was drilled in the side of the housing and it is held in place using small screws.	Punching a Hole in Plastic For the man and owl moulds this hole punch was used to create a small hole in both pieces of vacuum formed plastic. Paper fasteners were used to hold the housing in position.

Year 8 - Moisture Tester Project

PCB Circuit

This is the circuit before any components are added to it.

Circuit with components in place

The components have now been put into position.

Components Box

This is the component box. Here you will find everything you need to build your circuit.

The Soldered Circuit

This photo shows the circuit with all the components soldered in position. Now the excess wires need to be removed.

Transistor

LED (Light Emitting Diode)

Component Display Boards

This is a display board explaining LEDs and Transistors. These boards located in are in each of the Technology workshops.

Resistor

Resistors determine the flow of current in an electrical circuit. Where there is high resistance then the flow of current is small, where the resistance is low the flow of current is large. Resistance, voltage and current are connected in an electrical circuit by Ohm’s Law.

Resistor Colour Code Chart

Resistors are too small to have numbers printed on them and so they are marked with a colour of coloured bands. Each colour stands for a number. Three colour bands shows the resistors value in ohms and the fourth shows tolerance. We can calculate the value of a resistor using this chart.

Soldering Iron

This is a soldering iron. It is used to melt solder wire and help make an electrical connection within a circuit. (You can read more about soldering by clicking the button below.)

Wire Strippers

Wire strippers are used to remove the plastic coating and expose the metal wire so it can be soldered to components/circuits.

Long Nose Pliers

These pliers are used for both cutting and gripping wires. Their namesake long gripping nose provides excellent control and reach for fine work in small or crowded electrical enclosures.

Side Cutters

These pliers are used to cut the wire to the correct length.

Vacuum Former

Vacuum Formed Plastic

Moulds Loaded into Vacuum Former

Moulds

Gerbil Cutter

Gerbil cutting out moulded plastic

The Moisture Tester

This picture shows the completed moisture tester. The LED is located on the body of the ladybird and the circuit is held inside the housing.

Drilling a Hole in Plastic

For the ladybird mould a hole was drilled in the side of the housing and it is held in place using small screws.

Punching a Hole in Plastic

For the man and owl moulds this hole punch was used to create a small hole in both pieces of vacuum formed plastic. Paper fasteners were used to hold the housing in position.