The ECG UConn BME 290

Buffers

What is a buffer? –Non-inverting amplifier with a gain of 1 Why use a buffer? –Buffers provide a high input impedance

C2 and C3

At high frequencies a capacitor acts as a: A.Short circuit B.Open circuit At Low frequencies a capacitor acts as a: A.Short circuit B.Open circuit

C2 and C3 What do they do? –C2 and C3 act to remove any DC component of the signal Why would you need to do that? –If the signal received from the body has a DC offset it will be multiplied by the diff amp

Differential amplifier

Differential Amplifier V1 & V2 are in the microvolt range We need it to be in the milivolt range so Rf/R1 is set to ~1,000 If C2 and C3 had not existed, it is possible that a 10mv offset could exist between V2 and V1 This 10mv offset would then be multiplied by 1,000 (Gain) which would set to 9VDC

1 st Order LPF

The ECG is known to be a low frequency signal A LPF can be used to remove the high frequency noise in the signal How do you pick Fc?

T Filter design using Fast Fourier Transform (FFT) Problem –How to find a suitable cutoff frequency for the ECG filter Solution –Use the FFT –The signal exists below 40 Hz –Noise at 60 Hz?

Summing Amplifier

The ECG signal Goes below 0 VDC Microprocessor has an input range from 0 to 5 VDC Need to add a dc offset to the signal so that the signal stays within the input range of the microprocessor

Microprocessor

Provides Analog to Digital (A/D) conversion Transmits digital data serially to the Isolator

Digital Isolator

Isolates the patient from the computer

RS232 Converter

Converts Serial digital signal from TTL 0,5 VDC to RS232 format 10,-10 VDC