PROMPT - Project for Recording, Observing, and Measuring Parachute Tube

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The pressure inside a standard parachute bay should be between 8 and 15 PSI when the parachutes deploy. In case that value is incorrect, a significantly overrated sensor was chosen. The selected sensor also has considerations for the attachment of a measuring tube, to allow the sensor to be situated away from the bulkhead, therefore reducing wiring complexity. This measurement tube will be run through the bulkhead and to PROMPT wherever it is mounted.

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Data Reporting:

PROMPT will be connected to the backplane through the standard RS485 interface provided on the sensor board. This interface also provides a 5-volt supply for PROMPT. In the event that an RS485 connection cannot be established, PROMPT will log its data locally.

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PROMPT is primarily intended to operate off of the regulated 5v provided from the backplane through the sensor board's connection. To allow for PROMPT to be utilized independently, the power system should be rated to allow for the direct connection of a 1S LiPo battery. This will include all the requisite battery protection circuits, such as reverse-polarity protection and over-current protection. Current consumption is expected to be <100mA, closer to 30-50mA. A jellybean priority mux circuit will be implemented to force a selection between the 5v and battery connections. The output of this mux will then go through a boost converter to regulate it to a clean 5 volts.

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Human Interface:

2 debug LEDs will show the state of PROMPT at a glance. A CP2102N is integrated on the board to act as a UART-USB bridge, providing both a debugging interface and a means of downloading data from the board if it is being operated independently of the backplane. 

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Component Selection:

0-60PSI pressure: ABP2LANT060PG2A3XX

• Used by Sparkfun
• i2C interface
• Not on JLCPCB

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Thermocouple Amplifier: MAX31855 

• Used by Adafruit
• 3-Wire SPI interface
• Cannot be used with grounded thermocouples
• JLCPCB: C52028

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Memory: W25Q128JVSIQ

• Same as most other devices on the backplane
• JLCPCB: C97521

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• Widely used by Adafruit and similar
• Input range from 0.5 to 5.5v
• Output adjustable from 2.2 to 5.5v
• 3.7A max current
• Pass-through mode when VIN > VOUT
• JLCPCB: C919459

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