As you can see I've now built the voltage follower and driven-right-leg circuitry. I've connected the 390kOhm resistor at the O/P of A2 through two 40kOhm resistors to each input of the INA. Is this what you were suggesting?
With this setup I get the following voltage readings (again measured with the negative end of the probe connected to the negative of my power supply):-
Pins 1 & 8 are at ~2.5V.
Pins 2 & 3 are at ~3V.
Pins 4 & 5 are at 0V.
Pin 7 is at 5V.
Pin 6 (the output pin) is at ~40mV but this without any inputs connected to the inverting and non-inverting inputs. All I have connected to them at the moment is the resistors and the right-leg feedback you suggested. Do these values look ok or are they unexpected?
FYI, the source for my bias voltage is a voltage divider. I'm using a voltage regulator to insure that the voltage from the power supply is at 5V, then I've connected two 100kOhm resistors between the 5V and ground, and I'm tapping the bias voltage from the centre point...
hi,
This is in line with what I would expect, the inst amp 'cancels' the common mode input voltage of ~ +2.5V and so the amp output should be near zero.
This is what you have measured.
Taking Ron's point, which inst amp are you working with.???
Please advise and if necessary post the correct datasheet.
If you look at the ECG cct you have posted, you will see that on the patients ankle is ~ +2.5Vdc.
This is the same voltage at the junction of the 40K's on the circuit.
The 40K's you have added, simulate the resistance of the patients body, between the ankle point
and the other two points on the patients chest.
Ideally the 'bridge' formed by these 4, 40K's should be in balance and both ints amp inputs should be identical, ~ near +2.5V.
Your task now is to 'inject' a low level voltage into the bridge, so that the amp senses and amplifies
the 'difference' on the inst amp INV & NI inputs.
You could simulate this by having a variable resistor in place of one of the 40K that you have added.
eg: a 39K and a 2K multiturn pot in series.
This will give ONLY a dc level change in the output of the amp..
The remainder of the circuit expects a 'pulse' [ac] signal from the patients heart...
To fully test it you will need to inject low level pulses into the input bridge.
DONT use +/-12V on this circuit as some has suggested.
Do you follow.?
Why have you taken on such a complex project.?