Digital Pca; Microcontroller; Thermistor Circuit - Respironics Alice PDx Service & Technical Reference Manual

D PCA
IGITAL
M
ICROCONTROLLER
Refer to Alice PDx Digital Board Schematic sheet 3 located in the
Schematics section beginning on page 53.
The system microcontroller is a Microchip dsPIC33FJ256GP710. Key features of this part include:
•
256 KB Flash program memory
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32 Kbytes static RAM
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32 Analog inputs
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2 UARTS
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2 SPI ports
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2 I2C ports
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The ability to access many peripherals via DMA
The microcontroller is responsible for coordinating the operation of Alice PDx system. Analog signals are
received from the various sensors and processed by their respective conditioning circuits. These signals are
then passed to the microcontroller where they are further processed for storage on the SD memory card.
T C
HERMISTOR IRCUIT
Refer to Alice PDx Digital Board Schematic sheet 1 located in the
Schematics section beginning on page 53.
The thermistor circuit provides the interface between a nasal or oral thermistor and the system microcontroller.
Current flow through the thermistor, via resistor R137 causes a voltage to be developed across the thermistor.
Slight variations will occur in the voltage across the thermistor in response to resistance changes due to patient
respiration. These voltage variations will be coupled through a low pass filter, consisting of R155 and C50 and
then through a highpass filter consisting of R145 and C210. The filtered signal is then amplified by U38A and
low pass filtered by R293 and C211 before being sent to the LT1867L 16 bit ADC.
A THERM_GOOD signals the microcontroller when a plug is inserted into jack J6.
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Amplifier gain: 31
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Lowpass filter cutoff: 16 Hz
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Highpass filter cutoff: 0.033 Hz
P 18
AGE
NOTE
NOTE
TM
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Alice PDx Service & Technical Reference Manual
1054417, V . 01
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