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Moisture detector

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Electronics Coursework Aim: For my project I plan to build a moisture detector which can be used too see if the ground on the cricket crease is too moist or dry. It will measure the level of water in the ground and show the moisture level by lighting a different LED. So if it was a hot day with less water in the ground the moisture detector will only light up a green LED, then as the water in the ground increased another LED will light. Yellow for when the moisture level is in the middle of the scale and red for when the ground is too moist and so unsuitable to play any cricket. The first sub-system to consider is the input. I will put two contacts in my circuit so the processor can compare the resistance of the water. ...read more.


The diagram above is my preliminary investigation using LED's, by changing the 5K potentiometer the light will have more voltage or less voltage. The 100 ? resistor protects the LED, so not too much current is allowed through. By doing this preliminary investigation I knew that I could use LED's in my circuit, as I would have between 1.8V and 5V for them to run off. Secondly, I have also investigated the Op-Amp before. In a circuit with an Op-Amp (see diagram below) there are two resistors which hold the voltage for the non-inverting input (pin 3), these two stay the same. Then for the inverting input (pin 2) there is one resistor and a variable resistor, which can change the voltage allowed through it. As the voltage between the two resistors for the inverting input changes, from high to low then the output will change. ...read more.


Then at wetter levels more LED's will light, then when it is too wet the circuit will turn on three red LED's, warning the user. * Draw as little current as possible, less than 50mA. This will increase the amount of time the circuit can be run off a single battery. Block diagram of proposed system: The input will just be the two contacts that are put in the ground. Depending on the resistance of the water a signal is feed into the Op-Amp. Then the Op-Amp will send a high or low signal into an IC chip that will display the relevantly coloured LED. My circuit is restricted, as I could build a circuit that has an Op-Amp for each LED. But this would take too long and make fault finding extremely difficult. Only the cost is not restricting, as even if I built an Op-Amp for each it would still be very cheap to do so. Graham South Electronics - 1 - ...read more.

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