BIOPIC Heartbeat Monitor
Approx construction cost US$64
Take a peek at the rhythmic waveforms that keep you ticking!
Before joining EPE, the author was on a short-term contract with a life-support equipment manufacturer. Of particular interest were the heartbeat waveforms displayed on the heart defibrillator screens, which had to match certain software criteria before electric shock treatment could be given to patients. The various categories of waveform could be simulated electronically, but in active service the system would monitor a patient's heart via chest electrodes.
Inspired by the simplicity of the heart monitoring circuits, the author designed one for EPE. This was published in Feb/Mar '93 as the Biomet (which loosely translates as Life Meter). PIC microcontrollers were unheard of to hobbyists at that time and the three-board design required 13 i.c.s. Heartbeats were monitored across the chest using simple electrodes. Pulse rates could be monitored separately by a handheld sensor that detected the opacity of the thumb, which changes as blood pulses through it. A 3.5 digit liquid crystal display (l.c.d.) showed the pulse rate. Data could also be output to a computer for waveform display.
Although heart monitoring techniques may not have changed fundamentally since that design, the methods for processing the data have moved on dramatically. The Biopic design presented here takes advantage of a PIC16F876 microcontroller's capabilities and uses an alphanumeric l.c.d. screen, plus an electrically-isolated serial data link to a PC-compatible computer. There are only five i.c.s. The probes and contact pads used are those sold inexpensively by major chemists for use with proprietary TENS (pain relief) machines.
The design can be used as a handheld unit without using a PC. In this role it outputs heartbeat waveforms to the l.c.d., which is used in the same graphical fashion as with the author's Micro-PICscope (simple oscilloscope) of April '00. The display also shows the heartrate in beats per minute using a program written for QB (QBasic or QuickBASIC). (Note that the Biopic software is self-contained and does not require QB itself to be installed. The QB program can be run in DOS mode or under Windows 3.1, 95, 98 and ME (other Windows versions have not been tested with it and no advice can be offered for them).
More details on this construction project can be found in the June 2002 issue of EPE Online, the world's first web-delivered electronics and computing hobbyist magazine.
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