I am trying to design a proximity sensor that works only in the dark using LDR and IR transmitter and receiver. I have looked at some circuits (this tutorial and this video) and some people have used MOSFET or om-amps in their circuit, is there a voltage signal that has to be amplified? I am still confused why do we need them? Why can't one just make a circuit with few resistors and a potentiometer that will control the sensitivity of the circuit?
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\$\begingroup\$ Amplification (of voltage or current) is just half of the story. More often than not, you need a transistor or an op-amp to make the (biasing/sensing) circuit as much as independent as possible from its load (the rest f the circuit that uses the voltage or current produced from the sensor). \$\endgroup\$– Sredni VashtarCommented Nov 28, 2016 at 1:36
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\$\begingroup\$ What type of (fairly simple and mostly unuseful) circuit might you be referring to? \$\endgroup\$– Andy akaCommented Nov 28, 2016 at 8:42
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\$\begingroup\$ @Andyaka Well as a beginner I am trying to boost my skills in electronics so the circuit may be unuseful but good enough for a noob to start with. I am looking to make a circuit similar to the one in the tutorial link and then move to a circuit that is in the video link. \$\endgroup\$– Hamza HussainCommented Nov 28, 2016 at 8:59
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2 Answers
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Many (most?) kinds of transducers are not capable by themselves to interface to the Real World. They produce rather "fragile" signals which must be amplified (or maybe at least "buffered") to maintain signal integrity perhaps over a long distance back to a controller, etc.
Or in many cases a local circuit is used to produce a "threshold calculation" to send a binary/digital signal. We don't really want to know what is the ambient light level. We only need to know whether the light beam is interrupted or not.
answered Dec 3, 2016 at 15:48
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Opamp is not used for only amplifying. Basic functions of opamps are to suppress common mode noise, to amplify of course etc.
When you implement this circuit on breadboard you will see the difference between circuit with opamp and without opamp.
