Tuesday, December 15, 2015
EOG Amplification Circuit Fritzing Diagram
Ultimately, the Notch and OpAmp circuits never worked correctly. For this semester I will be working with the EOG circuit amplified through the Instrumental Amp IC INA118P. This signal is a bit noisey but does still distinguish left eye movement from right eye movement.
This circuit is not sensitive enough to detect something as small as REM, but is a great starting point for exploring EOG Arduino interface because IT WORKS.
The power supply should be 12V 1A for the L7805s I am using, but the only adapter I have that works with the circuit correctly is 2A. Ideally, the L7805s would also be a different variation of the same regulator, LM7805. Theoretically there is no difference, but in reality I do get an output voltage of 8.6V when it is supposed to give me 5V from one regulator, and a 3.3V from the other. Something here isn't working correctly, but I've studied the circuit intensely and following the instructions for it soundly so my suspicion is either the 12V 2A adapter is effecting it, or the difference between LM7805 and L7805.
The L7805 circuit takes the 12V power supply and regulates it down to a smooth 5V. The reason we are using two supplies is to drive the differential amplification between the two electrode inputs. Thus a power supply ground is created from the 12V supply, and a second, virtual ground, is made from the output voltage of the second regulator.
The INA118P takes the signal input and amplifies it with a gain of +500 (giving us a net gain of +501 to the signal). We use a 100ohm resistor to set the gain. There is a chart on the INA118P's datasheet that shows how to set the gain with different resistors.
When we move our eyes the electrical signal from the skin polarizes the corresponding electrode and raises or lowers the voltage. A GND electrode is connected to the forehead and to the virtual ground of the 7805 series. This signal is output as a single voltage to the Arduino's Analog 0 input and the ATMEGA328P converts it into a digital value we can then use in programming (ADC).