|A comparitor as the name suggests compares 2 voltages and rapidly changes
from either fully saturated (positive) or fully saturated (negative).
Most experiments made using a comparitor use a 741 op amp, this
is a very common chip that is used in electronics, whilst not a specialist
comparitor chip, the very high gain makes it suitable for this application.
Not part of GCSE electronics syllabus it is useful to know how to wire
up such a device, any further studies will definitely require this.
The power supply going to the 741 op amp(comparitor) is provided using
a dual volt power supply, both the negative 9 volt and positive 9 volt
can be used to provide the supply to the chip.
You could if necessary wire 2 batteries together, wiring the + and -
terminals together (see below), the remaining output terminals being used
to supply the 741 chip.
Also be aware that the output will be signal will swing between + and
- 9 volts unlike a more conventional output of 9 volts and ground.
Temperature controlled comparitor
The circuit below shows a 741 op amp connected to sense the the temperature
(using a thermister) in a green house.
When the temperature reaches a certain temperature then the comparitors
output will change.
An LED will light up but it could also trigger a motor connected to
a window to allow the greenhouse to be ventilated.
You will need to understand the layout of a comparitor
ciruit and the effects of the voltages on the inverting and non inverting
When the non-inverting input (V+) is at a higher
voltage than the inverting input (V-)
The output saturates at the highest positive
When the non-inverting input (V+) drops below
the inverting input (V-)
the output saturates at the most negative voltage
it can output
Try filling in the following form
You should also be able to label the inverting,
non inverting and output of the comparitor
Hint - The inverting is marked (-) input A, the
non inverting (+) input B, the output marked Vout