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Amplifications to USB PIC32 Starter Kit II

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Saraa

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Hello Everyone,

I am working on a project which deals with PIC32 starter kit, I/O Expansion Board and an amplifier.. I am actually running the ADC10 code on my micro-controller and taking an Analog input from a function generator then display it on the computer...

According to my specifications, I am entering a sine wave with an amplitude of 10 mVp-p (offset = 0 mV, from -5.0 to 5.0 mV) and frequency is 50 Hz .. Since PIC32 doesn't deal with negative (-ve) values due to its internal reference voltage (0-3V), it shows an output of half sine waves which is correct and as expected...

However; using the amplifier by inputting those half sine waves result in producing complete sine waves?!!! is this correct or is it an abnormal behavior ?!! ... In other words, does the amplifier amplifies the signal and shift it ?!!!

Thanks...
~ Sara
 

FoxyRick

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That would depend entirely on your amplifier - it certainly can do so if that's the way it's designed, and adding a voltage offset to the signal is the easy way to get all of it into your PIC without having to resort to a negative rail and external ADC.

I take it you mean that you are connecting your signal generator directly to the amplifier, thus giving the amplifier the full-range AC signal.

What exactly is the amplifier - do you have a schematic for it?
 

Saraa

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I am using the SA02 Amplifier,
**broken link removed**
 

FoxyRick

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I've had a look - while there's no schematic, we can assume a few things from its specifications and intended use.

It's a single-ended design intended for applications which can obviously be AC. The 4Hz minimum input hints that the input is AC coupled with a capacitor, then it is probably biased at half the supply voltage at the input to the first op amp. Effectively, the AC 'zero' line has been shifted up to a few volts.

So, it is doing exactly what you have guessed - offsetting the whole input signal into positive, then amplifying the result.
 

Saraa

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Thanks a lot for your replies, I really appreciate it :)
 

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