1. ECG Measurement System By Nick Rose Under guidance of Dr. Jack Ou Summer 2012 Built off of Chia-Hung Chen, Shi-Gun Pan, and Peter Kinget’s design for an ECG Measurement System from the Columbia Integrated Systems Lab

2. Full Circuit R=10 M Potentiometer 9 V Gain= 200

3. Bandpass Filter Transfer Function

4. Op-Amp Purpose: To bias voltage at output of AD624

5. Opto-Coupler

6. V(1) versus V(2)V(1) versus V(3)

7. Instrumentation Amplifier Gain of 200

8. Gain of 1000

9. V(3) of op-amp versus: 2 nd Harmonic Distortion3 rd Harmonic Distortion

10. Gain of 200, V(3) of 741 op-amp = -4.4 V Adjusted V(3) to -4.4 V to minimize 2 nd and 3 rd harmonic distortion Magnitude of input sine wave versus gain (gain includes gain of opto coupler)

11. Power Dissipation The entire circuit (AD624, 741, optocoupler).. Current draw: 114 mA Voltage: dual power supply (+-9V)

12. Shielded Versus Unshielded Cables Untwisted cable, shielded by aluminum foil Aluminum shield is grounded

13. Unshielded AD624 Output

14. Shielded AD624 Output

15. Unshielded ECG Output

16. Shielded ECG Output

17. Shield Input of ECG

18. Unshield Input of ECG

19. Shielded AD624 Output at DC

20. Shielded AD624 Output (0 -12.5 Hz)

21. Shielded AD624 Output at 60 Hz

22. Unshielded AD624 Output at 60 Hz

23. Unshielded ECG Output

24. Shielded ECG Output

25. Extra Components for stabilizing the Output Voltage of the AD624 10 Mohm resistors were used at pin 1 and 2 of AD624 in order to provide bias current transistors in the pre-amplifier stage An input offset potentiometer with the middle pin attached to +9 V was used to reduce offset voltage. The voltage at pin 9 was used.

26. Different Design Iterations Breadboard PCB Equipment

27. Future Work: Active Grounding Technique Problems observed: – Common mode sensing resistors attached to node 16 and 3 of AD624 can affect of node 9 of AD624. 25 Kohms, DC voltage at node 9 is disturbed. 1 Mohm, DC voltage at node 9 is stabilized. – Large values of Rf makes it difficult to for negative feedback to pin node 2 of 741 op-amp to ground. – What is the right ratio of Rf/Ra?