S.K said:
Hi,
So the pot have to be connected at the 1st stage OPA to control the gain?
Where does the Vref comes from?
And by using R1 and R2, i can control the Vhi and Vlo?
S.K
Hi,
I would recommend that you have a pot on the 1st stage to control the Gain of the instOPA while you are experimenting with sensor/circuit.
The Vref comes from a resistor potential divider [Ra.. Rb], choose say, to have 1mA flowing thru the divider from the +3V supply [Ra+Rb=3K].
You can then calculate the value of the low end resistor Rb, so that you have +0.5V at the junction of Ra/Rb, with respect to the 0V.[Rb=0.5/0.001=500R] You may have to use preferred values of resistors. Ra=2K7 , Rb=560R, will give +0.51V..
You will have to calculate a resistor divider for the Vref on the Comparator.
If for example, you wanted the Comparator to switch at about +0.25V it would require a Vref of about +0.25V
For the initial test you can leave off R2, until you get the comparator working.
Your problems are due to having to many unknowns in the project.
eg: you dont know the strength of the hearts magnetic field and the direction of the magnetic field relative to the sensor.
I would connect the mag sensor to a high sensitivity oscilloscope to determine what magnetic field strength/direction,
I would expect to see close to the heart.
From that, I would know what level of Gain I would require and what the compartor threshold would have to be.
REMEMBER: If you do carry out trials on humans with your project, get qualified advice on any potential electrical hazards
before working close to the human heart.
Eric