AN206

Vishay Siliconix

www.vishay.com

S FaxBack 408-970-5600

6-2

Document Number: 70604

10-Aug-99

Micro

Controller

PC

FIGURE 2. Patient Simulator Block Diagram

Temperature

Oxygen

Saturation

Pulse

Rate

To Patient

Monitor

RS-232

Design Considerations

The temperature parameter was simulated by using a discrete

resistor array and a pair of analog multiplexers as illustrated in

Figure 3. A discrete resistor value representing a known

temperature was placed between the same channel of two

analog multiplexers. Using its I/O lines, the microcontroller

simultaneously selects one of the 16 resistors. A know current

is sent through the resistor. The medical monitor reads the

voltage drop across the resistor and translates it into a

temperature reading.

accurate results, it was necessary to use the multiplexers with

a low on-channel resistance. The temperature simulation

section of the design utilized the DG406, a 16-channel

multiplexer manufactured by Vishay Siliconix. Thus, it was

possible to simulate 16 discrete temperatures by using a pair

of multiplexers. The DG406 was ultimately chosen for its low

measured and confirmed several times. To get the best results

possible, lower resistor values were used and a digital

potentionmeter array was used to get the exact resistance

required including the 40-

Simulating the saturated oxygen level was accomplished

utilizing another DG406 multiplexer. An analog signal was sent

through the selected channel of the multiplexer and attenuated

in a predetermined manner. The resulting signal is then output

to the medical patient monitor modifying the saturated oxygen

parameter. Again an array of digital pots was used to

compensate for the already low on-resistance and to get the

exact resistance values desired.

FIGURE 3. Temperature Simulation Circuit

DG406

DG406

From mC

Monitor

I

Digital Pots