How Can an Op-Amp Comparator Circuit Monitor Soil Moisture Levels?

[natural]

A botanical laboratory requires an op.amp. alarm circuit which will indicate when the soil in a plant pot is not moist enough. With the assistance of the in information below design such a circuit remembering to include suitable values for any resistors used.
when two copper probe wires are inserted into the soil 15cm and the soil is wet, the resistancw between them is 1.3kohms. However as the soil dries out the resistance increases and reaches a value of 85kohms when the soil is too dry.

All i know is to use a wheatstone bridge. from here i am lost can someone please help.

 

[berkeman]

Hint1: Form a voltage divider with that soil resistance and some other fixed, appropriate value resistor. Then sense the mid-point voltage of this voltage divider, using an opamp in the comparator configuration (just guessing this is what you are supposed to do, based on your thread title).

Do you know how to hook up an opamp to serve as a comparator? Hint2: positive feedback is the key (why?). Hint3, use google or wikipedia or your textbook if you don't know what a voltage divider or comparator configuration are.

Then show your work here if you are still having problems, and well see if we can offer more hints.

 

[m2003]

I would recommend using a comparator op.amp circuit to design the alarm system for the botanical laboratory. This type of circuit compares two input voltages and outputs a signal based on their relationship. In this case, the two input voltages would be the resistance values of the soil when wet and when dry.

To start, we can use the information provided about the resistance values of the soil to determine the suitable values for the resistors in the circuit. Since the resistance between the copper probe wires is 1.3kohms when wet and 85kohms when dry, we can choose resistors with similar values to create a voltage divider circuit. This will allow us to convert the resistance values into corresponding voltage values for the comparator to compare.

For example, we can use a 1kohm resistor and a 100kohm resistor in series with the copper probe wires. This will create a voltage drop of 1.3V when the soil is wet and 8.5V when the soil is dry. These voltages can then be fed into the comparator circuit.

Next, we can set a reference voltage for the comparator to compare the input voltages against. This reference voltage can be set to a value in between the wet and dry voltages, such as 4V. When the input voltage is higher than the reference voltage, the comparator will output a high signal, indicating that the soil is too dry. When the input voltage is lower than the reference voltage, the comparator will output a low signal, indicating that the soil is moist enough.

Finally, we can use the output signal from the comparator to trigger an alarm or a visual indicator, alerting the laboratory staff when the soil is too dry.

In summary, the comparator op.amp circuit can effectively monitor the moisture level of the soil in the plant pot and provide an alarm signal when the soil is too dry. By carefully choosing the values of the resistors and setting a suitable reference voltage, we can design a reliable and accurate circuit for the botanical laboratory.