Creating a Moisture percentage detector for soil

[Arslan Siddiqui]

Hey Guys !
Actually I am working on a semester project of Automatic Plant Irrigation System ,In this I am adding a device that shows the moisture of the Soil at any time,
I have set the elements as below:
When the voltage across the terminals is 8.0 then the percentage displayed on the two Seven segment display as 99.
When the voltage across the terminals is 6.0 then the percentage displayed on the two seven segment display as 75
When the voltage across the terminals is 4.0 then the percentage displayed on the two seven segment display as 50
When the voltage across the terminals is 2.0 then the percentage displayed on the two seven segment display as 25
When the voltage across the terminals is 00 then the percentage displayed on the two seven segment display as 00
Can somebody guide me how can i implement and design this logic!

 

[Alec_t]

Welcome to EP!
What sort of probe is connected to 'the terminals'?
If your probe is the type which simply senses resistance, then the value measured will depend not only on the moisture content but also on the mineral content of the soil.

 

[Arslan Siddiqui]

Actually i have built the circuit that uses terminals for sensing the change in resistance and gives different values .of voltage at different values of resistances which change due the amount of water the in the soil . I have given above in my post is the Output i want to obtain from the input from the terminals but i cannot find the circuit element(encoder,decoder,..etc) which could implement the logic.

 

[Alec_t]

If the highest voltage is 8V then you could use a 2:1 voltage divider and feed the output to an A/D input of a suitably programmed MCU driving the display.

 

[BobK]

The circuit you need is an analog to digital converter. Look it up.

I agree with Alec that I would use a microcontroller with a built int A/D converter to this since it an handle both the conversion and the driving of the LED display with a single chip.

Bob