I'm doing an ECG project where I've built most of the front in circuit and once finished I want to sample with an ADC and then either plot or calculate heartbeat from.
Set up
This is the set up right now. Its running off two 9 volt batteries in series for positive and negative voltage. The diff amp's gain is set to 125 and the non inverting op amp is set to 19.5. This gives me a signal around -1 to 3.5 V's.
ECG wave
This photo is when the gain was a little higher for testing but shows the general wave.
The problems, I'm having are that the signal "moves"; its not always centered around 0. This is an example of when it drifted down Then I only have the peaks being read by the ADC. The second problem is the negative part of the wave. I've tried to add in a DC offset by a voltage divider on the output but just lose my signal. Any idea why the signal moves besides noise and only being a 3 lead electrode and more importantly can someone tell me what I need to do to add some DC offset to this configuration.
I'll either be using the arduino's or the mbed's ADC to sample the signal. Any help is greatly appreciated!
Set up
This is the set up right now. Its running off two 9 volt batteries in series for positive and negative voltage. The diff amp's gain is set to 125 and the non inverting op amp is set to 19.5. This gives me a signal around -1 to 3.5 V's.
ECG wave
This photo is when the gain was a little higher for testing but shows the general wave.
The problems, I'm having are that the signal "moves"; its not always centered around 0. This is an example of when it drifted down Then I only have the peaks being read by the ADC. The second problem is the negative part of the wave. I've tried to add in a DC offset by a voltage divider on the output but just lose my signal. Any idea why the signal moves besides noise and only being a 3 lead electrode and more importantly can someone tell me what I need to do to add some DC offset to this configuration.
I'll either be using the arduino's or the mbed's ADC to sample the signal. Any help is greatly appreciated!