Integrated Human ECG

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Follow along these 4 easy steps to make an ECG!

Made by: Emilie Chadwell and Madeline Dianis in BME 207 Thursday AM

The ECG we will be using has three components, an instrumentation amplifier to amplify the the small electrical impulse of the heart, a notch filter to remove the frequency of 60 Hz, and a low pass filter to filter out high frequencies and remove noise. First, determine the desired gain for the instrumentation amplifier. With an input voltage of 1 mV, the gain should be around 1000 to get an output voltage of 1 V. With the gain determined, use the equations that relate resistors to voltage to determine the four resistor's values. Next, determine the frequency to be removed with notch filter, in this case 60 Hz should be where the filter notches. 60 Hz is the interference from power lines. With the frequency determined, center frequency can be determined and subsequently the resistor and capacitor's values can be determined using the equations provided. For the lowpass filter, a cutoff frequency needs to be determined. 150 Hz was chosen to prevent higher frequencies from interfering with the signal of the ECG.

Following the provided schematics in the previous step, model the three components of the ECG individually in LTSpice and include the resistor and capacitor values found in step 1. The ECG will have the instrumentation amplifier, then the notch filter, then the low pass filter. The initial input for the instrumentation amplifier should be small, around 1 mV to mimic the heart's electrical impulse. The output of this simulation should be the input of the notch filter, and the output of the notch filter should be the input of the low pass filter. Run each circuit to get a simulated output. This will be useful when building the physical circuit and determining if the circuit components are working correctly.

Following the LTSpice schematics, build the physical circuits one at a time. Start with the instrumentation amplifier, then build the notch filter, then build the low pass filter. Each component of the ECG should be connected to the function generator and oscilloscope to track its functioning. For the instrumentation amplifier, ensure that the input voltage is amplified and the gain is close to the predicted gain. For the notch filter, ensure that the output voltage decreases at 60 Hz and increases above and below 60 Hz. If the circuit is not notching at 60 Hz, the resistor values will have to be tampered with until the notching occurs at 60 Hz. For the low pass filter, test at multiple frequencies. Low frequencies should pass through and at high frequencies the voltage should drop. Once each component of the circuit is tested, connect the three components. This can be done by using a wire to connect the output of the instrumentation amplifier to the input of the notch filter, and the output of the notch filter to the input of the low pass filter.

Attach three ECG electrodes to a human subject on both ankles and the right wrist. Connect these leads to the ground, input, and output of the integrated circuit. Connect the circuit to the oscilloscope. The output should be the subject's ECG. From here, you can measure the amplitude and distance between QRS impulses to determine BPM.