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circuit of voltage shifter

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Alberta

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Hello,

I'm working on project of ECG signal processin and using PIC controller. But the problem is that PIC doesnot take negative signals. So i've thought to use voltage shifter (i.e add a dc level in ECG signal). Can some one refer me some circuit for shifting the voltage by an amount of 1 or 2 volt. If some one has better idea than this then also tell me.
Thanks
 

As most simple solution, you can either use a voltage divider with two resistors, one connected to your signal and the other to VCC respectively the ADC reference. This implies a signal level reduction, e. g. by -20 percent for 1 V shift or -40 percent for 2 V (assuming 5V VCC). Or you can use AC coupling with a voltage divider at ADC input to define the bias level. RC has to be choosen large enough for undistorted signal transmission. I guess, ECG amplifier also has an AC coupling in the front end. Or you can use an OP circuit, that allows to set signal gain and offset independently.
 

Alberta,
You can use an instrumentation amplifier such as the Analog Devices AD524. Connect a positive voltage to the reference input pin to shift the output by the desired amount. This provides a very accurate method. The accuracy is limited by the accuracy of the reference voltage, and the offset voltage of the IA, which typically will be very small.
Regards,
Kral
 

Kral said:
Alberta,
You can use an instrumentation amplifier such as the Analog Devices AD524. Connect a positive voltage to the reference input pin to shift the output by the desired amount. This provides a very accurate method. The accuracy is limited by the accuracy of the reference voltage, and the offset voltage of the IA, which typically will be very small.
Regards,
Kral
Click to expand...

I think the idea of the reference voltage in the instrumentation amplifier ic is a very good idea. AD620 is also a great instrumentation amplifier.
I wanna ask about the best way for interfacing the ecg signal to pc ?? Is USB is better or Parallel port or Serial ??? And what about using the sound card in the pc as an ADC ??? I'm waiting for an answer .
 

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