[scorpio]

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.

[docvette]

Doc here,

Are you doing this HERE (USA ) or Singapore?

Here, the power company's are beginning to send DATA over the power lines..is why I ask..and in Singapore,have been doing it for some time:

FROM NETWORK MAGAZINE:
==========================
Powerline around the world

There are currently two main technology providers Switzerland's Ascom and Israel's Main.net PLC. Between them, they have helped to start PLC services in many countries including Germany, Sweden, Singapore and even the remote ski-resort cities in the Austrian Tyrolean mountains. In Singapore, the incumbent utility company Singapore Power (SP) started technical trials last November, using a test-site at the Singapore Polytechnic. Initial speeds of 800 Kbps and later 2.25 Mbps were achieved. Complete Text
========================


To isolate the cause, run your circuit on a Dedicated DC source only..and move as far away from power lines as the bench will allow..you can also "Sniff" the air with an AM radio on dead air..and listen for the oscillation.

Doc