If you want to generate 2.5V, then use a 1:1 voltage divider from 5V and feed it to in+ of OPAMP.
Connect OPAMP output to IN-.
Maybe you can use "virtual ground"
Your DRL circuit with C4 connected to R1/R2 will influence ECG signal.
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If you want to build an active voltage generator, then don´t use the high ohmic IN- inputs of the INA. Use the outputs instead.
The instrumentation amplifier is supposed to have its inputs biased at half the supply voltage or at 0V when using a dual polarity supply. Your inputs are not biased.
The opamp picks up the common mode signal (electrical hum) picked up by both electrodes and is fed out-of-phase to the patient's leg to cancel the hum.
Here is an ECG circuit that uses a dual-polarity supply:
The instrumentation amplifier is supposed to have its inputs biased at half the supply voltage or at 0V when using a dual polarity supply. Your inputs are not biased.
The opamp picks up the common mode signal (electrical hum) picked up by both electrodes and is fed out-of-phase to the patient's leg to cancel the hum.
Here is an ECG circuit that uses a dual-polarity supply:
Keep in mind for any Op Amp to be linear the inputs must be at the same voltage and that voltage MUST be within the linear input range of the IC. Some can go to both rails, but not both your IC's
INA spec's
Linear Input Voltage Range
(V+) – 1 to (V+) – 0.65 upper limits
(V–) + 1.1 to (V–) + 0.95 lower limits
Note your design with TLC277 (+in) is grounded with a single supply.
That only works with a split supply , same as audioguru's example.
Therefore change gnd to V/2 for +in on DRL amp (pin3)
You do not need a TLE2426 "rail splitter" IC that has an output current as high as 20mA because the load in your circuit at half the supply voltage is almost no current. Wwo resistors and a capacitor will replace it.
Thanks to all of you for your suggestions. I took them into account and learned some usefull things about in-amps.
Seems like the problem was with the active electrodes. I replaced them with some wet electrodes and the signal seems fine now.