What does it do?
| The non-inverting amplifier subsystem is used to amplify an analogue input signal. |
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How does it operate?
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Click on the circuit diagram to download a Livewire file of the circuit that you can investigate and add to your own circuit. |
The non-inverting amplifier circuit uses an operational amplifier, or op amp, to amplify the signal.
The signal is amplified relative to a reference signal, which is fixed at half the power supply voltage by the potential divider R2 and R3.
An alternative is to use a pair of power supplies, +Vs and –Vs, and then the reference signal is 0V. |
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Operational amplifiers have two inputs, an inverting input ('-') and a non-inverting input ('+').
The amount of amplification, or gain, can be varied by changing RF and R1, where RF is the feedback resistor.
In this formula, the input voltage and the output voltage are measured relative to the reference voltage, which is half the supply voltage Vs. |
The LM324 is a suitable inexpensive IC, contains four operational amplifiers and can work from a d.c. power supply with a voltage anywhere between 3 and 32V.
Possible applications
- Increasing the change in the voltage from an analogue sensor, such as a thermistor or a light sensor.
Making
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Pins of LM324IC
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How part of the PCB might look |
In the example PCB, the input signals goes to pin 3, and the output signal comes from pin 1. Any of the other three operational amplifiers in the IC could be used.
Build and test the unit that will provide the input signal before building the comparator.
Use a Dual In Line (DIL) socket for the IC. Before inserting the IC, connect the power supply and use a voltmeter to check that:
- the voltage on pin 11 is low (0V);
- the voltage on pin 4 is high (the supply voltage);
- the voltage on pin 3 (the blue PCB track) varies in response to the unit that provides the input signal.
Insert the IC the right way round.
Testing
Turn the potentiometer to its mid-point. Make sure that the signal going out (on the green PCB track) increases as the input signal increases.
Fault finding
If there is a fault, check that:
- The voltage on pin 11 is low (0V)
- The voltage on pin 4 is high (the supply voltage)
If there is a fault, check the tracks and solder joints.
Alternatives
- A PIC with an analogue to digital converter can respond to changes in an analogue voltage; PICs are more flexible but more expensive than a single LM324.
Web links
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