This thesis addresses realistic ECG-signal simulation for educational use. It focuses on understanding and verifying an existing circuit and on comparing its simulated and hardware implementations. The build is based on the Engineering World Health ECG-simulator design. In the first phase I assembled the circuit on a breadboard and measured it with an oscilloscope. The oscillator section required a fix (both load capacitors set to 22 pF and the series resistor removed) so the crystal would start oscillating. With the hardware running, I prepared an LTspice model in which I replaced part of the CD4521 outputs with time-aligned voltage sources, since the CD4521 could not be simulated directly. I concluded that the circuit consists of three main blocks: a 4.1943 MHz crystal with a CD4521 frequency divider providing the time base; a CD4017 counter that splits this base into timing segments; and resistor–capacitor networks with diodes that shape the P, QRS, and T segments.
The results show that the simulated signal matches a reference ECG well: the wave sequence is correct and the QRS is narrow and steep, with deviations mainly at the overly symmetric peaks of the P and T waves. On the breadboard the deviations are larger: the P wave is too sharp and too high, the R-to-S transition is not perfectly linear, and noise is present. The causes are primarily parasitic capacitances/inductances, long wiring, and imperfect contacts.
The project goals (hardware assembly, block-level analysis, and verification via measurements and simulation) were achieved. The main added value is educational: the modular simulator lets students swap components and directly observe their effect on the P, QRS, and T segments while also learning about cardiac function. Limitations: realism was assessed visually, and the EWH instructions would benefit from additions (crystal start-up guidance and indicative R/C values). Nevertheless, the outcome is a useful low-cost teaching aid and a solid basis for a PCB version.
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