Transcript LAICE Photometer Payload

Group # 21
TA: Kevin Bassett
David Schlais, Jamie Barber, Robbie Wankewycz
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Mission: Launch low-Earth-orbit satellite Jan.
2016
Study of how gravity waves deliver energy
from lower to upper atmosphere
◦ Can modify the structure of the upper atmosphere
◦ Can lead to added noise and disruptions in radio
wave propagation
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Gravity waves observed through “airglow”
Cubesat main objectives:
◦ Systematically observe gravity waves
◦ Create a global map of where gravity waves are
active
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Payload
◦ Photometers and Temperature Sensors
 Photometers: detecting photons of given wavelength
 Temperature: used for calibration (on the ground) of
what photon wavelengths passed the optical filters
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Objective
◦ Build control board to collect, process, and transmit
photometer and temperature data to satellite CDH
 Temperature sensors: <1 degree Celsius resolution
 Photon Counters: < 0.1% accuracy
 Power all items on the board using only the regulated
3.3v and unregulated 7.4v lines supplied by satellite bus
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Features
◦ PMT Fault detection
◦ Individual PMT shutdown during operation
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Signal
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Power
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Three objectives
◦ Photon counting
 Detect and count voltage pulses from 7 PMTs
 2V voltage spikes, 10ns in width
◦ Temperature collection
 Collect data from temperature circuit’s ADC
 SPI interface
◦ UART Serial Communication
 Transmit temperature and photon data packets
 8N1protocol, 152000 baud rate
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Photomultiplier Tubes (PMT’s) and optical
filters detect airglows
Temperature-dependent devices
◦ PMT signals become noisy at high temps.
◦ Optical filter bandpass varies with temp.
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Temperature sensing circuit will monitor
temperature of devices directly
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Operating temp. range:~(-5°C-+60°C); As
wide as possible
Steady excitation current of 300µA (or
.3mA) ± 50µA
Voltage output range of 0V - 1.5V ± 85mV
Temperature Resolution of 0.5°C ± 0.3°C
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Chosen for:
◦ Linearity
◦ Range and Accuracy
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Lead wires impact accuracy
US Sensor PPG102A1
◦ Accuracy of ±0.15 °C
◦ Increase of 4 Ω for every 1°C
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ADC provides temp.
resolution
Dynamic range
choices
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Translates resistance
into voltage
Can also use voltage
divider network
Ensures steady 300 µA
current
VoutU 11  VoutU 10
 300 A
RREF
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3-wire RTD configuration
Resistance of LEAD1 and
LEAD3 cancel
Voltage follower ensures
no current flow through
LEAD2
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Prepares sensor output to be converted by ADC
Temperature [ºC]
Resistance
[Ω]
Vin
[RTD]
Vout
[ADC]
175
1666.27
499.881 mV
0V
0
1000
300 mV
342mV
-50
803.14
240.942 mV
1.5V
VOUT  (5.794) VIN  1.396
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Incorrect values derived from simulation
Unable to employ exact resistor values
Imprecise resistor values
PCB imperfections
Measured: VRTD vs VOUT
2
VOUT [V]
1.5
1
0.5
0
0.25 0.27 0.29 0.31 0.33 0.35 0.37 0.39 0.41 0.43 0.45 0.47 0.49 0.51
VRTD [V]
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Connect circuit to ADC
Correct for hardware imperfections through
software (i.e. voltage offset)
Incorporate measured data into software
Optimize
Utilize and verify subsequent circuits with
measured results chart
Voltage Regulation and Power Switching
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Supplied by satellite’s power bus:
◦ ~7.4V (nominal) unregulated battery line
◦ 3.3V regulated line
◦ 300mA max
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Requirements for payload:
◦ 5V with 5% tolerance delivered to each of 7 PMTs
◦ 3.3V to each of 11 temperature sensor circuits
◦ 3.3V to FPGA
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PMTs are sensitive and expensive
Require protection schemes to allow
switching
◦ Over-light protection
◦ Over-voltage protection
◦ Over-current protection
◦ Control-loss protection
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Switching regulator for efficiency
Buck conversion with wide input range
Low dropout voltage
Output tolerance of 5%
PowerGood signal
fsw
Vin(min)
Duty Cycle
(max)
L
Iout
(max)
Cout
1 MHz
6.47v
.85
5.5 μH
1.325 A 20 μF
35.7 kΩ
.8 MHz
6.25v
.88
6.8 μH
1.31 A
49.9 kΩ
.6 MHz
6.04v
.91
9.17 μH
1.295 A 33.3 μF
71.5 kΩ
.4 MHz
5.85v
.94
13.8 μH
1.28 A
118kΩ
.2 MHz
5.67v
.97
27 μH
1.265 A 100 μF
25 μF
50 μF
Rt
255 kΩ
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Voltage Regulator Output vs Time with
fluctuating voltage input
Vout
Vout (reg)
OverCurrent
PowerGood
CurLim EN
Reg EN
Vin
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High current loops
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Trace resistances
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Ground plane
interferences
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Thermal dissipation
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Sensitive regulator in non-ideal conditions
◦ Layout
◦ heat
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Verification of chip damage and other issues
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Output voltage
Switching frequency
Internal reference voltage
Pin shorts
Drawn current
Drawn Current
160
Current (mA)
140
120
100
Over-current
80
60
40
20
0
0
20
40
60
80
100
Load Resistance (ohms)
120
140
160
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For prototyping and testing of FPGA code
prior to final PCB, we used a Mojo v3
Spartan6 dev board.
Same FPGA as final flight board
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Detected pulses from actual PMT (10ns width)
Test: 20ns pulses, 5MHz
◦ Sampled every 10 seconds via stopwatch
◦ Averaged over 11 repetitions
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Expected: 50,000 counts / 10 seconds
Results: 100,042.5 counts /10 seconds
◦ Max-Min within 1.6% of each other -- consistent
 0.16sec can be explained by reaction time
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Conclusion: software is double counting
0.022% accuracy < 0.1% tolerance
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SPI interface with ADC
◦ Never interfaced with ADC itself
◦ Inputs/Outputs follow SPI protocol
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FPGA acts as master in the SPI interface
MISO mapped to a pin directly for testing
Shifts in 0s and 1s accordingly based on pin
Still need control to implement MOSI
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Note:
◦ USB – RS422 breakout
◦ RS422 transceivers
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Based of Xilinx-based IP that comes with
Picoblaze 8-bit microcontroller
◦ Modified in this project to work without Picoblaze
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Works with 8N1 protocol
Detects four separate commands accurately
◦ 0x01, 0x02, 0x04, 0x08
◦ Ignores/deletes all other commands
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Sends 21 and 22 byte packets accurately
◦ Sends 21B photon count upon 0x04 command
◦ Sends 22B temperature data upon 0x08 command
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Single channel PMT (demo)
Multiple channels PMT
ADC_in tied to Vcc (during demo)
ADC_in tied to function generator
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Intra-project Integration
◦ Full PCB layout
◦ ADC integration
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Integration with rest of satellite
◦ Getting PCBs made
◦ Control and Data Handling (project group #12)
◦ Installation on satellite