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Build A USB-Controlled Electrocardiograph

It's controlled by a USB port on your PC or laptop and displays a person's electrocardiogram (ECG) on the monitor or LCD screen

By Jim Rowe

An Electrocardiograph is a piece of medical equipment used to measure and record the voltages (ECG) produced as a result of heart muscle activity.

By attaching electrodes (or ‘leads’ as they are known in the trade) to the skin of your wrists, ankle or chest, our PC-Driven ECG project can display, record or print out the same kind of ECG waveform on your personal computer.

Why would you want to build one? Well, looking at the waveforms generated by your heart can be both fun and educational.

Click for larger image
The complete ECG setup using our new Electrocardiograph, a laptop PC (with USB) and home-made electrodes. You can also use commercial ECG pads.

You can monitor changes to your heart under various conditions, as your heart is affected by many factors such as emotions, mental and physical activity – even breathing.

All of these things have a demonstrable effect on the heart’s ECG waveform. Being able to show this easily, safely and at low cost is an added bonus.

Professional ECG machines can cost anything from $4000 up, and while this project is not intended to be used as a diagnostic device, the displayed, recorded and printed waveforms are of a quality approaching that of professional machines.

Our new PC-based electrocardiogram is smarter than previous models because its operation is under the control of an inbuilt PIC microcontroller. It’s also faster and compatible with modern PCs, because it’s linked to the PC via a standard USB cable – thanks to the use of an Elexol USBMOD3 interface module.

And finally it’s easier to use, because all functions are controlled using a Windows-based GUI program, written in Visual Basic.

Both the PIC microcontroller’s firmware program and the Visual Basic PC program will be available on the SILICON CHIP website (www.siliconchip.com.au).

The PIC program (ECGSAMPL.HEX) is in hex code form ready for PIC programming, while the VB program (ECGCONTR.ZIP) is in the form of a zipped-up installation package. We imagine that kit suppliers will have already programmed the PIC for you.

You’ll also need a special USB virtual COM port driver which the PC needs to communicate with the ECG via a USB cable. This will also be available on the SILICON CHIP website, as R9052154.ZIP. Both the latter items can be installed directly on a PC running Win98SE or newer USB-compatible operating systems. Note that it won’t work with Win NT-based systems – not through any shortcoming in the design but the simple fact that NT doesn’t recognise the USB port.

PLEASE NOTE:
This project has not been designed for medical diagnosis. Correct interpretation of ECG waveforms and tracings is a complex and skilled procedure and requires medical training. The USB/ECG is presented here as an instructive and educational device only. If you are concerned about the health of your heart, consult your GP or a heart specialist.

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