Development of resistor decade

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Gájász Zoltán
Department of Automation and Applied Informatics

The project of my thesis was to design an electrical test circuit for an impedance measuring unit of the CA306B defibrillator designed by Innomed Medical Zrt. The task of my electrical circuit was to represent the human body’s resistance thats value differs in a wide range. I had to be able to produce a resistance value in the 0-16383 Ω interval with 1 Ω resolution. I can set the resistance by pushbuttons or by a PC.

The first step was that me and my consultant discussed the specification, then I created the plan of the system in which I defined the tasks of the units of the circuit.

After that I was searching for the appropriate components for my circuit. For this I had to ckeck the voltage and current levels of the components to be able to use the ones that can handle enough electric power.

I started the designing of the hardware by creating the resistance unit. After that I managed the connection between the microcontroller and the resistance unit via a relaydriver IC.

Then I designed the microcontroller, the pushbutton and the PC interface units. Finally I created the unit of the power source. I was taking care of preventing polarity problems and of filtering the voltage source. I used the Pads 3.1. circiut designer software for drawing the block diagram and the printed circuit.

After that I made the software that operates the circuit. The first component of the software is for setting the right resistance value, the second is for handling the pushbuttons, the third is for handling the PC connection.

In my thesis I describe the construction of the system and the operation of the units. I will describe the hardware units in 3 parts, the software units in 4 parts.


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