DARCI (Data Recording Instrument) is a clinical data collection and research quality assurance tool designed and built by Champlin Technologies LLC for Seattle Children’s Research Institute (SCRI). DARCI measures differential pressure of air from -5 to 30 cm-H2O on its inlet port (Luer lock taper fitting) with a resolution of 0.05 cm-H2O at 125 samples/second. DARCI has internal non-volatile memory for storing up to 120 days of continuously collected data. Through a USB virtual com port, a Windows program configures DARCI and downloads recorded data. The DARCI enclosure measures 4.5 x 3.5 x 3.5 inches (LWH) with a standard ISO19054 pole mount fitting attached on the back. A medical-grade plug-in AC transformer provides electrical power (5 Vdc) to DARCI. An internal battery and on-board non-volatile memory provide continuous recording and storage of data for up to 24 hours in the event of an AC power interruption or loss. A start button with a green LED and a stop button with a red LED provide the operational interface to the user or medical staff. Except for a small pressurization vent hole, the lid interface and all connectors and switches are sealed and installed with gaskets to support wipe-down.
DARCI has been used successfully during SCRI’s studies of its Seattle-PAP. For each of the premature infants enrolled in the latest study, one DARCI unit measured air pressure in the esophageal catheter (Pes) and a second unit measured air pressure at the patient airway/nasal interface (Paw). DARCI recorded air pressure data on internal memory for download and analysis. DARCI performed reliably and consistently throughout the various studies.
DARCI functionality is provided by two main components:
The on-board micro-controller is an Atmel SAM3X8E. The SAM3X8E is a 32-bit ARM Cortex-M3 RISC processor with an internal clock rate of 84 MHz and several power management features to support battery applications. On-chip features include 512 Kbytes of flash memory, 100 Kbytes of SRAM, high-speed (HS) USB port, 5 serial ports, 2 TWI interfaces, 4 SPI interfaces, 9 general purpose 32-bit timers, a Real-Time Clock (RTC), and 12-bit ADC and DAC. More than enough for this application. The 144-pin QFP package was used for the DARCI PCB. The SAM3X8E uses a JTAG interface for device programming.
The differential pressure sensor is a Honeywell HSCMRRN001PD2A3. It is a piezo-resistive silicon pressure sensor with a serial bus digital output for reading pressure measurements at 14-bit resolution. This is a high-end pressure sensor with on-board ASIC for calibration measurements and temperature compensation over 0 °C to 50 °C. The sensor used in DARCI measures pressure over the range of +/- 70 cm-H2O (+/- 1psi) and operates from a supply voltage of 3.3V. The pressure sensor is housed in an 8-pin DIP package with two ports for measuring differential pressure.
All of the internal electronic circuitry resides on a single two-layer circuit board measuring approximately 10 x 7 cm. Schematic capture and circuit board layout were created in Altium Designer. The bare PCB was fabricated by Sunstone Circuits located in Mulino Oregon.
The enclosure that houses DARCI is made of moulded high-impact ABS material. The LID and base incorporate a tongue and groove seal using a neoprene gasket. The lid is attached with four screws located outside the sealing area to avoid ingress of moisture and dust. A thermal screen process was used to fuse the ink into the ABS material keeping the surface smooth. Plastic Sales and Service Inc., located in Seattle WA, did the high-quality labeling on the lids.
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