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In this project, we will be simulating an EEG (or ECG) amplifier circuit using LTSpice. Other circuit simulation software can be used. (Figure below can be downloaded. Right click and save image.)
Figure 1. Schematic of an EEG amplifier circuit, which can be found in the resource link above.
Additional Resources:
Spice model for AD620N chip that is used in the circuit.
https://www.analog.com/en/products/ad620.html#product-tools
LM 358 Spice model
https://www.st.com/en/amplifiers-and-comparators/lm358.html#cad-resourcesPin numbers for LM 358
https://www.st.com/resource/en/user_manual/um0065-macromodels-user-manual-for-standard-linear-products-stmicroelectronics.pdf
example of nodal assignment Pin 1: negative input
Pin 2: positive input
Pin 3: Out
Pin 4: Vcc+
Pin 5: Vcc-
EEG Project with resources & step-by-step instructions
https://github.com/ryanlopezzzz/EEG (Alternative version of the amplifier circuit, shown below.)
Figure 2. Schematic of an alternative version of the EEG amplifier circuit.
Instructions:
Use the above link under ‘Additional Resources’ that refer to generating a spice model for an AD620N chip. The link explains how to create a new circuit symbol in LTspice for the AD620N chip.
For the input signal to the amplifier circuit, there are two sinusoidal inputs. For the amplitude of the sinusoids, a good range of values would be around anywhere from 50uV to 100uV. You can change the amplitude and phase of the two sinusoids. The amplifier amplifies the difference of the two sinusoids. The two sinusoids can have different amplitudes, phase, and frequency. The amplifier will amplify the difference.
Probe the node where the sound card is supposed to be, to view what the output signal looks like.
The frequency of the input signal can range anywhere in the range of EEG brain waves. Alpha waves: 8-13 Hz
Beta waves: 15-40 Hz
Delta waves: 0.1-3.5 Hz
Theta waves: 4-8 Hz
When setting up the transient analysis in LTspice, the stop time can be anywhere from 1us (microsecond) to 5us (microseconds). You can leave the step size and other parameters blank. Just the stop time is sufficient. Depending on the computer, CPU, and RAM, the simulation time can vary. When running the simulation, by pressing the ESC key, you can view the output voltage in real-time as LTspice is running the simulation. (Note: 5u stands for 5 microseconds and 5m stands for 5 milliseconds in LTspice.)
After running the simulation, you can probe the output node and/or the node where the audio connector goes that connects to the speaker.
Take a screenshot of this output graph.
Also, probe the input signals, and plot the difference of the input signals. Or, you can simply plot the two input signals separately.
Report submission:
Copy and paste the screenshots of the following:
Circuit schematic
Output voltage graph
Input voltage graphs (or a graph of the difference of the input voltages)
A short one sentence description under each figure describing what the that figure is about. (E.g. Under the output voltage graph, ‘Graph of output voltage of xx amplifier circuit that amplifies the difference of two input sinusoidal signals with amplitudes of 20mV and 18mV and frequency of 10Hz.’)
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