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chelleteng
04-10-2012, 04:04 AM
Need some help/ideas to solve this issue I'm currently facing with my ECG module:

The TL084 is supposed to work as an amplifier and filter, it keeps giving irregular readings (not sure if it's unfiltered noise, etc) and it wouldn't give a negative value for the ECG reading.
Despite changing the gain at R2, the reading still does not differ much.

Thank you.

Beau Schwabe
04-10-2012, 04:17 AM
Where is your 3rd electrode? typically there is a ground return to the body that allows the instrumentation setup to reject any common mode. In your schematic, this signal would typically be buffered from the mid-point of R2

HShanko
04-10-2012, 08:55 PM
What type of ECG sensor are you using? Vendor source if purchased?

Looks to be nearly what I need for my 'heart pulse display' using Raymans 3.5" touch LCD and pcb. Thanks for any info you can supply.

william chan
04-11-2012, 02:52 PM
Beau,

If the leg ECG sensor is connected to the mid-point of R2, would the voltage reference R8 and R9 still be required?
Should C1 be replaced with a resistor to provide direct DC coupling instead of AC coupling?

Beau Schwabe
04-11-2012, 04:47 PM
I would focus on Figure #14 of this documentation. It's a modification from conventional ECG in that it improves current loop problems created in the leads going to/from the patient... Ra in the schematic could be simplified by halving R1.

Just curious, with your current setup, what is the level of your noise floor? This needs to be extremely low in order to detect micro-volt levels picked up by the electrodes.

william chan
04-12-2012, 01:31 PM
chelleteng,

Could you post a picture of your TV screen to show us what could be the problem?

chelleteng
04-13-2012, 02:36 PM
When both the ECG inputs are short circuited:

916639166491665


When the ECG inputs are attached to both wrists:

9166791668


When the ECG signals are not attached to anything (noise, etc):

916669166991670


The heartbeat captured from the ECG circuit is very irregular. The number on the top left corner is the ADC reading from the Sigma-Delta converter.
Any ideas? Thank you..