Balloon Sensor Node Specs

The balloon sensor node is a configurable sensor package designed to be strung up the middle of a balloon envelope, returning valuable pressure and temperature data from our vehicle. Each sensor node has the capability to support one TMP100 Temperature Sensor, and two MPX50XX Family pressure sensors in the surface-mount package. Limits on I2C bus length are eliminated through the use of the P82B96 chip from NXP, boosting the voltage on the I2C lines to 12V, and decoupling our extended I2C bus from the main I2C bus. The pressure sensor values are converted to discrete digital data with an AD7992 I2C analog-to-digital converter. Voltages on the board are regulated by a Micrel Low-Dropout linear regulator. These boards feature solder jumpers to select I2C address for the AD7992 and TMP100 sensors. Up to 8 TMP100 addresses may be selected, and up to 3 AD7992 addresses may be selected (expandable to 5 with careful parts selection). These strings will be attached to eachother using 30 AWG stranded wire. 4 lines connect this bus together: 12V, Gnd, SDA and SCL.

PCB designs may be found here: http://github.com/Zuph/LVL1-Transatlantic-Balloon

The configuration of each variant will be described here.

Possible Mission Failure Points

  1. Sharp edges ripping envelope
    1. Concern
      1. During take-off or flight, horizontal acceleration might cause
        the PCB to come in contact with envelope
    2. Countermeasure
      1. Round PCB edges
      2. Wrap with heat shrink
  2. Sensor string or tubing entering gas exhaust vent
    1. Concern
      1. During take-off or flight, vertical acceleration might cause
        the sensor string or tubing to coil at the bottom of the balloon
        possibly entering the gas exhaust valve
    2. Countermeasure
      1. Place mesh over gas exhaust vent
  3. Sensor string or tubing tangling
    1. Concern
    2. Countermeasure

Weight Breakdown

Component Unit Weight Units Total Weight
30 AWG Wire .32 g/ft 200 ft 64 grams*
PCBS 4.3 g/board 3 boards 13 grams*
Pressure Sensors 1.4 g/Sensor 4 Sensors 7 grams
Tubing 1.75 - 2.16 g/ft 50 feet 87 - 108grams
Chips .5g .5g*
Fittings 1g / fitting 5 5 grams
Heatshrink .2 grams/tube 3 tubes .6 grams
Total 177 Grams - 198 Grams

White Star Bill of Materials

The following google spreadsheet details the parts we need for a complete sensor string, as well as their order status:

BOM Spreadsheet for Sensor Nodes

General Bill of Materials

The following table lists the parts needed to assemble a single sensor node:

Part Package Quantity Notes
P82B96 TSSOP 1 Requred to interface with >5v Bus. If bus is 5v, may omit and use jumper wires across appropriate surface mount pins.
TMP100 SOT23 1 Optional, up to 8 addresses configurable with solder jumpers.
Micrel 5205 SOT23-5 1 Required to regulate on board voltages. If incoming power is the desired voltage, may omit and use jumper wires across appropriate surface mount pins.
AD7992 MSOP 1 Up to 3 addresses configurable with solder jumpers. 5 addresses possible using combination of AD7992-0 and AD7992-1 parts. Required to interface with pressure sensors. If no pressure sensors desired, may omit.
MPXV50XX Pressure Sensors CASE 1351-01 Up to 2 May use any part numbers in this family with this package number, up to 2. May omit any or all.
10K Ohm Resistor 0804 2 R3 and R4 for AD7992
4.7k Ohm Resistor 0804 2 R1 and R2 for I2C bus (low side)
750 Ohm Resistor 0804 2 Filter Resistors for Pressure Sensors (Omit if sensor is unused)
.1 uF Capacitor 0804 3 C2, C3 and C5 Decoupling Capacitors
.01 uF Capacitor 0804 2 C7 and C9 Decoupling Capacitors for Pressure Sensors (Omit if sensor is unused)
1 uF Capacitor 0804 2 C6 and C8 Decoupling Capacitors for Pressure Sensors (Omit if sensor is unused)
.33 uF Capacitor 0804 2 C10 and C11 Filter capacitors for Pressure Sensors (Omit if sensor is unused)
470 pF Capacitor 0804 1 C1 Bypass Capacitor for Micrel 5205
10uF Capacitor 0804 1 C4 Decoupling Capacitor for AD7992

Balloon Sensor Node: Top

Major Parts

  • MPXV5050GP - 0-7PSI Differential Pressure Analog Sensor, plumbed to sense positive internal pressure
  • TMP100 - I2C addressable temp sensor
  • AD7992 - I2C addressable A/D converter for pressure sensor
  • P82B96 - I2C bus buffer - drops the 12v balloon signal bus down to 5v
  • Micrel 5205 - LDO regulator drops the 8-12v balloon power bus down to 5v

I2C Configuration Addresses

  • Temp Sensor:
  • Pressure Sensor:

Balloon Sensor Node: Middle

Major Parts

  • MPXV5050GP - 0-7PSI Differential Pressure Analog Sensor, plumbed to sense positive internal pressure
  • TMP100 - I2C addressable temp sensor
  • AD7992 - I2C addressable A/D converter for pressure sensor
  • P82B96 - I2C bus buffer - drops the 12v balloon signal bus down to 5v
  • Micrel 5205 - LDO regulator drops the 8-12v balloon power bus down to 5v

I2C Configuration Addresses

  • Temp Sensor:
  • Pressure Sensor:

Balloon Sensor Node: Bottom

Major Parts

  • MPXV5010DP - 0-1.45PSI Differential Pressure Analog Sensor, plumbed to sense positive internal pressure
  • MPXV5010DP - 0-1.45PSI Differential Pressure Analog Sensor, plumbed to sense negative internal pressure
  • TMP100 - I2C addressable temp sensor
  • AD7992 - I2C addressable A/D converter for pressure sensor
  • P82B96 - I2C bus buffer - drops the 12v balloon signal bus down to 5v
  • Micrel 5205 - LDO regulator drops the 8-12v balloon power bus down to 5v

I2C Configuration Addresses

  • Temp Sensor:
  • Pressure Sensor:

Sensor String Assembly

BOM per balloon

  • Tubing 50ft
  • (2) 1/16” barbed Tee fittings
  • (1) Sensor Node: Top
  • (1) Sensor Node: Middle
  • (2) Sensor Node: Bottom
  • (3) Heat shrink covers for sensor boards
hardware/balloonsensenode/v1.txt · Last modified: 2010/10/31 19:20 by tdmart05
 
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