WEEK SEVEN (2)

Bismillahirrahmanirrahim. 

This week I continue with circuit construction. The EOG circuit I found in the internet has six blocks. There are blocks for virtual ground, instrumentation amplifier, low pass filter, DC filter, amplification filter and block for electrodes.

The virtual ground block in my EOG circuit consists of an amplifier of LM358 with two 10kΩ resistors. In electronics, a virtual ground or virtual earth is a node of a circuit that is maintained at a steady reference potential, without being connected directly to the reference potential. In some cases the reference potential is considered to be that of the surface of the earth, and the reference node is called "ground" or "earth" as a consequence.

Instrumentation amplifier in my circuit consists of two 100kΩ resistors and a 270Ω resistor. The IC used for this block is INA126P. This block also has two input from electrodes.

The DC filter block removes the uneven DC signals to smooth DC signal. This DC filter uses only a 1uF capacitor and a 160kΩ resistor. 

For low pass filter block diagram, it consists of two 27kΩ, and a 2uF capacitor with a LM358 IC.  Basically, an electrical filter is a circuit that can be designed to modify, reshape or reject all unwanted frequencies of an electrical signal and accept or pass only those signals wanted by the circuit designer. In other words they filter-out unwanted signals and an ideal filter will separate and pass sinusoidal input signals based upon their frequency. Low-pass filter is a filter that passes low-frequency signals and attenuates (reduces the amplitude of) signals with frequencies higher than the cutoff frequency. The actual amount of attenuation for each frequency varies depending on specific filter design. It is sometimes called a high-cut filter, or treble cut filter in audio applications. A low-pass filter is the opposite of a high-pass filter. A band-pass filter is a combination of a low-pass and a high-pass. 

The electrode’s block consists of the right and left electrode with V_off, V_amp and frequency of measured value. 

The final amplification block for the output stage is meant to transfer maximum power to the output device. In order to transfer maximum power at high efficiency, push-pull arrangement is employed in the output stage. 

Barakallah.