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

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The temperature sensing inside the parachute bay will be accomplished using a temperature sensor screwed directly into the bulkhead between the avionics and payload bays. For the booster, the temperature sensor will be on a set of breakaway wires through both bulkheads. The most likely approach that will be taken to implement this is to put a barrel jack on the bulkhead of the booster, which is then connected to with a barrel plug. This will provide the greatest chance of a proper pull-out, but may not provide a reliable connection and may introduce errant resistance, skewing measurements. 

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Pressure Sensing:

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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Remote Connection:

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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Power Systems:

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 2S LiPo battery. This will include all the requisite battery protection circuits, such as reverse-polarity protection and over-current protection. This will be achieved using an LDO.

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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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RS485 Transceiver: MAX487

• Slew-rate limited
• UART interface
• JLCPCB: C9953

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Microcontroller: 

• Unknown, probably STM32

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Memory: W25Q128JVSIQ

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

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