TEST NANOSAT PHOTOMETER TEAM

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TEST NANOSAT PHOTOMETER TEAM

• Illinois Nano-Satellite
• UIUC
• Ahmad A. Moatesim
• Mobeen A. Chaudhry
• Rodrigo Martinez Duarte

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TEST Thunderstorm Effects in Space Technology
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Block Diagram Interaction with other units
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Engineering Project Goals

• Ultimate goal of project
• - Design counter circuit to count number of
  photons hitting PMTs and relay counts to main
  computer.
• - Design additional sub-systems to enable
  computer- controlled, and light-activated,
  shutdown of the various PMTs, and other
  power-consuming systems.
• Relationship to other projects
• - Systems will be incorporated with instruments
  that Matt is designing.

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Description

• Nano-Sattelite works in the dark side of the
  orbit (around the earth). That is the active
  region since too much light will damage the
  PMTs.

FOR MORE INFO...
http//courses.ece.uiuc.edu/cubesat/
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Team
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Photo Multiplier Tubes
Mobeen A. Chaudry
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Photometers

• Two Kinds
• Background Photometer
• Two Hertzberg Photometers

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Background Photometer

• Important Features
• Operates in visible region
• Gain 0.75M to 1M
• Dark count
• min80
• max400

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Hertzberg Photometers

• Bigger in size and weight
• Features
• Work in UV to Visible region
• 185nm to 680nm
• Output Pulse
• 2.0 V to 2.2V

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ISSUES

• Wavelength problem
• Solutions
• 1) Make circuit for Bare Tube photometer
• 2) Swap the tube into built module
• 3) Use Filter to cut the visible light region
• 4) Get it manufactured by Hammamatsu

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Counter Circuit

• Rodrigo Martinez

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Introduction

• The counter has various purposes
• Determine the number of photons hitting the PMT
  in a given time. These readings will allow the
  ground station to determine the activity of the
  airglow layers in the atmosphere. Regular counts
  are expected to be 20, 000 to 100,000 in 1 sec.
• The counters are overdesigned and are capable
  to count up to 16 MHz. This consideration will
  serve us to know when we have entered the
  inactive region of orbit (when the sun bombards
  the PMT with far more photons).
• The count will also help the processor to take
  the decision whether or not to shutdown the PMTs
  when the light sensor detects excessive light.

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Objectives

• Counter with the capability to count up to 224
  photons in each sample period.
• The smaller the size the better due to spacecraft
  available space. Height has to be less than 3.9
• Max number of output lines 16.
• Max number of input lines 10.
• Count has to be accurate within square root of
  the signal.
• Small power possible, preferably below 3 W.

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General schematic
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One counter schematic
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Decoder and Shutdown Circuit
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Performance Against Objectives

• It can count up to 224 photons in a given
  period. In our case the sampling period is one
  second, making it capable to count up to a photon
  frequency of 16.777 Mhz.
• Maximum height given by the BNC connector 0.5
• Dimensions of the board 4.5 by 3.5
• Because of the counter IC chosen we could cut the
  output lines in half (8). Also the reading
  process becomes straight forward and very quick.
• The input lines were reduced to 7. Use of a
  decoder to reduce input lines.

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Performance Against Objectives

• Error of 0.08 for counting frequencies from 1 Hz
  to 16.5 MHz.
• Accuracy stays within the square root of the
  signal with frequencies up to 1.5 MHz.
• 2.5 W of maximum power required for operation at
  5V.
• Introduced a shutdown circuit controlled by the
  processor in order to save power in the inactive
  region.
• Introduced a voltage regulator for the power
  input making it possible to work in a wide range
  of voltage supplies (min 7 V max 35 V).
• BNC interface to PMTs.

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Functional Test

• Worked with different frequencies and had
  switches acting as inputs. Manually controlled.
  At this stage the OR stage at the first counter
  wasnt implemented.
• 1 KHz for 1 minute 60,225
• 100 KHz for 60 sec 5,995,413 5,930,259
• 1 MHz for 10 sec 9,924,308
• 7Mhz for 2 sec 14,828,742
• V ARIABLE ERROR FROM 5 TO 10

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TEST With Processor

• First test with the processor
• 3.333 MHz for 1 sec 4,287,656
• ERROR 8.63

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Functional Tests

• Add of the OR stage at the FIRST counter input.
  Tested with the processor. With frequencies below
  255 Hz the count came out right except at very
  low frequencies (1 to 100 Hz) counter wasnt
  cleared completely and just kept adding counts
  in every sample.
• From 255 Hz to 64KHz got an offset of 255 pulses
  approx.
• From 64 KHz to 16 MHz got an offset of 65,800
  pulses approx.

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Design Stage
We were getting the wrong output from the
counter. The right count is stuck just before
the register inputs. It is necessary to give one
pulse to the REGISTER to get the right count.
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Functional Tests

• Also the counters clear is synchronous so it
• was necessary to add an auxiliary clock to all
  the CLK
• and REG inputs of the counter in order to clear
  all the
• counters. This made necessary to add two more
  input
• lines to the four we got at the beginning.
• Tested with the processor getting the final
  readings
• 10 Hz for 1 sec 10
• 20 KHz for 1 sec 20,015
• 100 KHz for 1 sec 100,080
• 16 MHz for 1 sec 16,012,949
• 16.5 MHz for 1 sec 16,513,353

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Final Board made, GERBER Files also made
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Shutdown Circuit

• Rodrigo Martinez

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Introduction

• The shutdown circuit purposes are
• Protect the PMTs against burn out since they
  will be damaged if exposed to too much sunlight.
• Save power in the inactive region of orbit.
• Detect when the satellite has entered the
  inactive region of orbit.
• Shutdown the PMTs at any given time.

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Objectives

• The shutdown circuit can be activated either by
  the processor or by the light detectors.
• The processor has to have the final decision to
  whether turn the PMTs on or off.
• The processor has to have the ability to override
  the light detectors in case the later goes wrong.
• Have feedback from the shutdown circuit to the
  processor in order to know when and where too
  much light has been detected.

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General Schematic
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Performance Against Objectives

• The circuit is activated by both
• the light detectors in case of too much light
  detected
• and the processor when we want to save power.
• The processor can activate or deactivate the
  circuit regardless of the light detector output.
• Feedback established. If the circuit is activated
  an interrupt will take place in the processor.

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Functional Tests

• Simulate the PMTs as 100 ohms resistors.
• When circuit deactivated, current through the
  resistor was 52 mA with a constant voltage drop
  of 5V.
• 0 V across resistor when circuit is activated.
• Different Power Supplies can be used, we just
  have to vary the resistance in series with the
  PMT until we get the right voltage drop.
• For now the circuit is using trimpots to vary the
  reference voltage and using power supplies to
  simulate the light detector output.

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Recommendations

• Put high precision resistances to set up the
  reference voltage, once this is determined.
• Use power resistances in series with the PMTs to
  reduce the risk of having too much voltage or
  current through the PMTs.

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Board Made, GERBER files also made
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Temperature Sensors

• Rodrigo Martinez

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Introduction

• The temperature sensors will serve us to make
  better interpretations of the instruments
  readings.

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Objectives

• Sensors have to be analog, since we are
  interfacing them through its analog inputs.
• Working range from 50 C to 35 C.
• Small and robust sensors.

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Design
A voltage divider with a 5V power supply.
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Performance Against Objectives

• The Thermistors have a working range from 50 C
  to 250 C.
• With the correct choice of the fixed resistor a
  linear behavior in certain range can be achieved.
• Fixed resistor value 2400 ohms
• Range -50 C to 35 C

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Performance Against Objectives

• Values of the output voltage were obtained every
  5 C in the range mentioned before. These values
  where stored in the software for post-processing.

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Functional Tests

• Tested thermistors in different environments.
  Store resistance values.
• Compared this values with the table provided by
  the thermistors manufacturer. SAME RESULTS.
• Designed voltage divider. Got voltage outputs.

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Recommendations

• Use High Precision resistors for the fixed ones
  so the voltage output will only be dependant on
  the thermistors resistance

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Software Procedures

• Power up
• EN1
• While(1)
• Send out (F0) //prepare to clear
• Send out (F2) // clear pulse
• Send out (F0)
• Send out (01) // start counting
• Send out (00) // stop counting
• Send out (02) // auxiliary pulse
• Send out (00) // Read LSB first counter
• Send out (10) // Read MSB
• Send out (20) // Read HSB
• Send out (30) // Read LSB (second counter)
• Send out (40) // MSB read (second counter)
• Send out (50) // HSB read (2nd counter)
• Send out (60) // LSB read (3rd counter)
• Send out (70) // MSB read (3rd counter)
• Send out (80) // HSB read (3rd counter)
• // end of while loop!

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A
OUT0 OUT1 OUT2 OUT3 OUT4 OUT5 OUT6
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B
Output Of Processor
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C
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D
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CE
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AC
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EN
ENABLE COUNTER
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Results Every experimental
reading showed a 0.08 error 10
Hz for 1 sec 10 20 KHz for 1 sec
20,015 100 KHz for 1 sec 100,080
16 MHz for 1 sec 16,012,949 16.5 MHz
for 1 sec 16,513,353
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• Temperature Measurement
• How?
• Temperature to corresponding resistance already
  stored in Data Structure, array in my case, in
  sorted, low to high, order.
• Use of binary tree search O(n)log(n)

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0
1
2
3
4
5
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7
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Low Index
Higher Index
Reference Index (H.I. L.I.)/2
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Temperature Measurement

• If(input voltage lt voltage at reference index
  (reference-1) !lower index)
• Higher Indexreference index
• Reference Index(Lower index Higher Index)/2
• else If(input voltage gt voltage at reference
  index (reference index1)!higher index)
• Lower IndexReference Index
• Reference Index(Lower Index Higher Index)/2
• else
• if(data is present at current slot) return
  value
• else if(data is present at the left of current
  slot) return value
• else if(data is present at the right of current
  slot)return value
• else
• DATA NOT FOUND! ESTIMATE BY LINEAR
  INTERPOLATION.

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Results
Analog Temperature Program
Temperature (Centigrade Celsius) Vout
-50 0.131349
-45 0.178784
-40 0.239808
-35 0.317125
-30 0.413223
-25 0.530504
-20 0.671141
-15 0.835887
-10 1.024765
-5 1.236349
0 1.46771
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Questions and Inquiries

• Costs
• Matt Maple mmaple_at_uiuc.edu
• Submit questions
• Software moatesim_at_uiuc.edu
• PMT mobeen_at_uiuc.edu
• Hardware dmartnz_at_uiuc.edu