Hello all,
Ive been learning about op-amps in class and came across an EEG block diagram that uses a common reference(IE the earlobe electrode) and cant figure out how they did this. I thought it would be cool to have an EMG and a EEG device as a fall project.



In eagle this is what ive tried: Note this is with an AD623, single supply, with a voltage diver TLE2426(had to make a custom footprint in eagle).


Would I still need to bia's the input even though VREF sets the midpoint? Been trying in lab for past few days now, to no avail. Any help or reference to get this up and running would be much appreciated. After I plan on adding second order butterworth filters to help with noise.

 

The arrangement shown does not match what I have seen

 

For starting out learning to monitor biological signals, I suggest measuring EKG with a single differential instrumentation amplifier. Follow safety guidelines for connecting electrodes to humans and two 9 V batteries to create a split power supply isolated from AC mains.

 

Certainly using 9 volt batteries to power an EKG measurement system would avoid any probable shock hazard.
Once again, the circuits shown thus far are not similar to what I have read from reliable sources. I suggest reading the applications literature from a semiconductor manufacturer, such as Analog Devices or Texas Instruments. I would not trust ANY information from the cartoon channel, although a bit of it might be correct.

 

Do you understand the purpose and function of the reference connection??
It is to keep the input voltages centered within the operation range of the inputs. A second purpose is to protect from over-voltage to the inputs.

 

@feryuu
a little history,
ecg, eeg et all
there have been some posts over time on the forums,
some of them have been very dangerous, the poster not listening to the forum members.
in general, be very carefull ,

 

NOT ON THIS THREAD!!! Only 9 volts from a weak radio battery. No shock hazard in this thread!!

 

NOT ON THIS THREAD!!! Only 9 volts from a weak radio battery. No shock hazard in this thread!!

I read that as well @MisterBill2

but as you might be aware , other threads have started similar, and ended up with potentially dangerous circuits,
and wanted to make certain @feryuu was aware of this, as Im certain you remember in detail @MisterBill2