Subsystem: P6

Task Title:
Moisture Detecting
Op Amp Comparator

Introduction and Aims

By using an Op Amp Comparator (P6) and a Potential Divider (IP1), we will make a system that can detect if water or moisture is present. We will see that the process module P6 produces a very distinct On/Off signal to control the output device. This is useful in digital (logic) systems as they only recognise logic 1's and logic 0's.

Subsystem Circuit and Block Diagram

 

IP1
Moisture
Sensor
P6
Op Amp
Comparator
OP1
Sourced
L.E.D.
   


Investigating the System

Using the "Library of Subsystems" here and the circuit and block diagrams above, complete the following:

1, The moisture probes and VR1 form a Potential Divider circuit. The value of VR1 should be ohms. (See IP1)

2, The resistor R1 in series with the 10K resistor also form a potential divider circuit. If the voltage between them is exactly half the supply voltage then R1 = K Ohms. (See P6- Op Amp Comparator).

3, The "-" input to the comparator is called the input.

4, The "+" input to the comparator is called the input.

Modelling the System/Circuit

There are different ways to model and test circuits before components are soldered to a P.C.B.. Modelling is an important stage as it helps you spot any problems and make modifications more easily.

Method 1: Breadboard

Using this method, components are pushed into the interconnected holes as shown in the diagram below. The lines shown, indicate which holes are internally connected.

Print this page and by using the circuit diagram above, design the breadboard layout for this system.

Method 2: Computer Simulation

To begin, ask your supervisor if circuit simulation software is available on your PC. This method allows you to build up your circuits quickly and cheaply in a virtual environment but will not give you hands-on experience of the components you will be using when finally soldering your P.C.B..

Method 3: Using OnTrack modelling hardware

See P6 project guide.