Power line interference ?!

[kikilala]

Hi,

I am building my amplifier circuit for ecg and examining it

by using an oscilloscope. The circuit consists of instrumentation

amplifier(gain = 10), high pass filter(0.5Hz, gain = 3)and

low pass filter(150 Hz, gain = 35). The voltage is regulated at 5V.

Without feeding any input to the amplifier, I get the square wave

(or attenuated sine wave) with frequency 50Hz and peak-peak voltage

= 8V on oscilloscope. Is it really due to the power line

interference and why the noise has such a large amplitude?? Will it

affect my ecg signal?? and how to eliminate it? Thank you for

reading my post and hope that you can clear my doubt.

 

[plugwash]

so in other words you've built a circuit with a total gain of 1000 and a freqency band that includes 50hz and you were surprised that you got mains hum?! , to get decent results you are going to need to get the 50hz ripple on your power bus down to well below a millivolt.

the first thing i'd do is stick a bigass electrolytic (say 470uf) accross the power rails.

failing that what exactly does this 5V regulated supply consist of? is it a a lab pack or something you've put together yourself?