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ECG Patient Simulator

A low-cost solution

created by Frank Weithner

One of the most important test equipment in the biomedical workshop is the ECG Tester or

Patient Simulator. The Patient Simulator is connected to the ECG monitor and delivers the

typical ECG signal. Only with such a tester an ECG monitor can be repaired, the functions

and alarm settings checked and loose connections of the patient cables be located. A Patient

Simulators usually costs several hundred dollars and is unaffordable for small hospital

workshop specially in developing countries.

But the realization of an electronic circuit which creates an ECG signal must not be too

difficult and expensive. Here I want to introduce you my solution. Only a handful cheap

electronic devices are used. No special or exotic IC is needed. All parts should be available in

the nearest electronic shop or can be found on old electronic boards from your workshop

store.

This circuit consist of a handful electronic devices which delivers a quartz crystal stable ECG

signal for 60 and 120 heart beats. Only common electronic parts are needed and the building

costs are below 20 $.

Function:

The above shown ECG signal is complex and will be created by different single signals. The P,Q,R,S,T signals are formed in different steps and then are put together in the right

sequence. A shift register does the sequence job, RC combinations the frequency and

amplitude of the single waves.

IC1 contains an oscillator and a shift register. At the output of pin10 a signal with 16 Hz

triggers IC2. IC2 is a counter with 10 outputs. When output 0 of IC2 is active (pin3) the R-C

combination R8, C5 creates the P-wave. When the counter jumps to output 3 (pin7) the R-

wave is created by R4, C4. The negative part is reduced by the two diodes and simulate the

following S-wave. When output 5 is active (pin1) the T-wave is created by R7 and C5. The

outputs which are not connected create the needed pauses between the signals. All signals

are put together through R3 and R6 which level the respective amplitudes.

Pgina 1 de 3Frank's ECG Simulator

29/08/2011http://www.frankshospitalworkshop.com/electronics/diy-ecg_simulator.html

When one sequence is finished the shift register stops. Output 9 (pin11) is connected with

EN-input (pin13). Only when a reset pulse reaches the counter (pin15) the counter starts

again. This reset is also created by IC1. Because in addition to the 16 Hz trigger signal the IC

also provides a 1 Hz and a 0.5 Hz signal at pin14 and pin15 which correlate a heart beat rate

of 60 and 120 (switch 2). Therefore the square signal has to be transformed in a positive

needle pulse. This is the duty of the combination C6, R11, D4, R10. Because this pulse

comes earlier or later (0.5 Hz or 1 Hz) only the lengths of the U period is shorter or longer.

The PQRST wave form is not effected.

A small LED D3 with resistor R5 connected to output 3 (pin7, IC2), flashes during the

R- period.

The final resistor combination R12-R15 converts the bipolar signal from the electronic board

into the needed three pole output signal.

Note: The circuit is designed for common electronic devices. All parts can be found on old

electronic boards or at the nearest electronic shop. But if you have problems to find the clock-crystal of 4.1943 MHz you can take a 4.43 MHz PAL-crystal from a TV. Your output signal is

as good as with the clock-crystal but the heart rate will change to 63 and 127 beats per

minute.

(large image) (large image)

Part list:

R1 = 4K7

R2, R8 = 1M

R3, R4, R9, R10, R11, R12, R13 = 100K

R5 = 1K

R6, R7 = 470K

R14, R15 = 220

C1 = 22 p

C2 = 82 p

C3, C4, C5, C6 = 220n

IC1 = 4521

IC2 = 4017

D1, D2, D4 = 1N4148

cristal = 4.1943 Mhz

D3 = LED 3 mm

2 x IC sockets 16 pin



Here the first design:

Here the second version:

(large image) (large image)

(large image)

http://en.wikipedia.org/wiki/Electrocardiography

http://de.wikipedia.org/wiki/QRS-Komplex

4521

4017

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