UVM CricketSat Manual
What’s a CricketSat?
Description
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•
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Wireless temperature sensor
Usually flown on a balloon
Simple circuit
– Easy to build
– Easy to modify
•
Operation
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Low cost (~$10)
•
Produces tone or pulses related to
changing temperature
Transmits the tone wirelessly over a
radio frequency (RF) link
Received tone frequency measured
with an instrument or computer
software
Calibration graph used to convert
tone frequency back to temperature
The CricketSat Program at UVM
• Freshman introduction to engineering
• Sensor and system development
• HELiX / EPSCoR High School Outreach program
– 2003: Waldorf High School, VT
– 2004: Milton, VT and JDOB Boston, MA
– 2005: Milton and Brattleboro, VT
• University collaboration
– Medgar Evers College, City University of New York
– University of Alaska
• Awards (2005)
– Massachusetts State Science Fair, 1st Place (JDOB School)
– HELiX Symposium Poster Presentation, 1st Place (Shared, Milton
and JDOB schools, presenting separate posters)
CricketSat Background
CricketSat Origins
• Developed at Stanford
University
– Space Systems Development
Laboratory
• Part of the NASA student
satellite program
– Crawl, Walk, Run, Fly
– Teach fundamentals of space
hardware development
– Space Grant Fellowship
Program
• Funded support
• Vermont Space Grant
Consortium (VSGC)
Student Satellite Programs
• CricketSat
– Lowest cost - disposable
– Live telemetry
• BalloonSat
– Larger balloon
– Expensive instruments
– GPS tracking system
• CanSat
– Dropped by parachute from
plane or rocket
– Many instruments
– Live telemetry
– Test bed for CubeSat
• CubeSat
– Earth-orbit satellite
CricketSat Sensor Circuit
• Oscillator frequency
determined by temperature
• Oscillator output signal
modulates RF carrier
frequency
Receiving Station
• Receiver extracts oscillator
frequency from radio signal
• Oscillator frequency
measured by instruments
or software
• Calibration charts used to
determine temperature
CricketSat Schematic Diagram
Power Supply
Transmitter
Temperature Sensitive Oscillator
CricketSat Circuit Board
Transmitter
Custom Circuit
Prototype Area
Oscillator
Power Supply
Sensing the Temperature
Thermistor Device
• Resistance changes
with temperature as
shown in the graph
• Requires additional
circuitry to produce an
measurable electrical
response
• Use with an oscillator
circuit provides a simple
and low cost solution
Thermistor
Temperature Sensitive Oscillator
Thermistor
• Produces an oscillation that
changes with temperature
• Circuit based on the popular
555-Timer IC
• Oscillator frequency
determined by two resistors
and a capacitor
• Resistive and capacitive type
sensors may be substituted
• In our case, the upper resistor
is replaced with the thermistor
• Changes in temperature affect
the oscillator frequency as
shown in the chart
Frequency vs Temperature
• Oscillator Frequency
– Increases with warmer
temperatures
– Decreases with colder
temperatures
• Finding the Temperature
– A calibration graph, similar to the
one shown right, allows the
temperature to be determined
The Wireless Connection
• Oscillator output signal enables radio transmitter during charging
interval of the timing cycle
• Oscillator frequency is mixed with radio (RF) carrier frequency to
provide the wireless connection
Detail Operation – Power Supply
Power Supply Operation
• 9 Volts unregulated supply
– Max power to RF transmitter for maximum range.
• 5.0 Volts regulated supply
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5-Volt regulator (U2), 5.5-20 Volts input, 5.0 Volts output
Provides constant output as battery discharges (dies).
Required by oscillator circuit for consistent operation.
May be required for student-added circuity.
• Short-circuit protection
– Prevents damage with reverse battery connection.
– 5-Volt regulator has built-in protection.
– Diode D2 added to protect RF transmitter module.
Detail Operation - Oscillator
Oscillator Demo
Thermistor
R1
555 Timer IC
Vcc
LED
R2
Voltage on capacitor C1
Digital
Output
Signal
C1
Not Used
Capacitor
Charge &
Discharge
Waveform
Time
Simulation courtesy of Williamson Labs: http://www.williamson-labs.com
Oscillator Circuit Operation
• Based on the popular 555 timer IC design.
• Timing components
– Capacitor C1 is the electrical charge storage vessel.
– Resistors R1 and R2 behave as electrical conduits for the
charge to flow into and out of the C1 capacitor.
– R1 is a thermistor whose resistance (conductivity) varies
with temperature.
– The timer, U1, monitors the operation and the discharging
of the C1.
– Timing is completely controlled by R1, R2 and C1
represented by the formula:
f ( Hz )   1.44  R1 2 R 2 C 1 
Oscillator Circuit Operation
• Oscillator operation
– Voltage level on C1 oscillates between 1/3 and 2/3 of the
supply voltage (5 Volts).
– Charging interval
• Voltage increases on the capacitor with charge entering from the
series combination of R1 and R2.
• The timer IC monitors the voltage on the capacitor waiting for it
to rise to 3.33 Volts.
• Once it does, it begins to discharge it through R2 alone.
– Discharging interval
• The timer now monitors the voltage on the capacitor until it drops
to 1.67 volts.
• At this point, it ceases the discharge and allows the charging cycle
to repeat.
Oscillator Circuit Operation
• Timer Output
– The timer also provides a digital output relating to
capacitor charging and discharging .
– The output pin is high during the charging interval and
low during the discharge interval.
– The output drives an LED for visual cue as well as the RF
transmitter.
• Temperature Relationship
– The resistance of R1 increases with colder temperatures
causing the charging interval to increase, and thereby
reducing the oscillator frequency.
– The opposite effect occurs for warmer temperatures.
Detail Operation – Transmitter
Power Supply
Transmitter
Temperature Sensitive Oscillator
RF Transmitter Operation
• Purpose
– Modulate (mix) 434 MHz “carrier”
signal and 555-Timer output signal
– Amplify and transmit signal through
antenna sized for 434 MHz
• Common Types of Modulation
– FM: Frequency Modulation
– PM: Phase Modulation
– AM: Amplitude Modulation
• Analog
– Ex: Audio
• Digital (CricketSat)
– Amplitude Shift Keying (ASK)
– Also known as….
– On-Off Keying (OOK)
AM and FM Waveforms: Washington State University,
http://cbdd.wsu.edu/kewlcontent/cdoutput/TR502/page21.htm
Assembly Equipment List
• Assembly and Repair
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Soldering iron and solder.
Wet sponge or paper towel to clean the soldering tip.
Diagonal cutters for snipping excess wires and leads.
Small portable vise to hold board while working.
Solder wick or a solder sucker for removing excess solder.
• Testing
– Digital multi-meter
– Oscilloscope (optional)
– UHF radio receiver
Assembly Preparation
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Safety
– Use safety glasses while assembling the CricketSat. Hot solder and flying leads can
injure your eyes.
– Most surfaces of the soldering iron are very hot, will burn you and leave a blister.
Hold the soldering iron by the handle.
•
Follow the directions
– There are plenty of opportunities to mess up this project by rushing the assembly or
winging it on your own.
– Components that are soldered in place incorrectly are nearly impossible for an
untrained person to reinstall correctly.
•
Component orientation
– Many components are polarized or have pin-outs requiring proper orientation in the
circuit board.
– Pay close attention to instructions concerning the proper placement of those
components
– The components outlined in Blue on the following page are not polarized, and may be
installed in either direction.
•
Organization
– Make a hard copy print-out of the following page to assist your CricketSat assembly.
– Placing the actual components on top of the corresponding images will help identify
components and orientation markings.
C1
C2
R4: 100 Ohm
C3
C4
C5
C6
Negative
White
Band
Non-Polarized
Components
Brown-Black-Brown-Gold
R2: 3300 Ohm
0.1 micro-Farad Capacitors
Black Band
+
-
+
-
+
Longer Lead
Pin 1
U3: RF Transmitter
+
Notch
47 micro-Farad Electrolytic Capacitors
R3: 680 Ohm
Dimple
1
2
3
4
DIP
Socket
SW1
Pins: 1 2 3 4
Orange-Orange-Red-Gold
D2 - Diode
Blue-Gray-Brown-Gold
8
7
6
5
U1: 555
Timer
IC
D1
U2
R1
Flat Side
Up
Pins: 1 2 3
On/Off Switch
5-Volt
Regulator
Velcro
10K Ohm
Thermistor
B1: 9-Volt Battery
Printed Circuit Board (PCB)
+
Red Lead is Positive
Battery Snap Connector
Antenna Wires
-
+
Longer
Lead
+
Light
Emitting
Diode (LED)
Printed Circuit Board
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Purpose
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Composition
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To provide mechanical support and
electrical connectivity for components.
Circuit board composed of metal layers
(conductors) on epoxy (insulator) board.
Metal traces provide the wiring connections
between electrical components.
Via holes connect the two metal layers
Green insulating layer covers metal, except
at pads and holes.
Front side of board
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Install components on this side of board.
White silkscreen
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Component placement outlines.
Reference designators to associate
components to schematic diagram.
Back side of board
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Most of the soldering is done on this side of
the circuit board.
Assembly Techniques
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Inserting Devices
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45 degree angle is best
Soldering
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Bend leads at a right angle on diodes and
resistors to allow insertion into board.
While pressing component to board, bend
leads outward at 45 degree angle.
This will hold components in place while
soldering.
Soldering iron must touch component lead and
metal pad on circuit board.
Apply solder to intersection of all three.
Once solder melts, feed liberally for about one
second.
Remove the solder first, then the iron last.
Do not dab or paint with the soldering iron.
The soldering iron should stay fixed in position
while feeding the solder quickly.
The finished solder connection should look like
a shiny Hershey’s Kiss ™.
Bend lead close to board
Snipping leads
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Use safety glasses to protect your eyes.
Hold lead while cutting or point downward.
Snip just above solder joint
Power Supply Circuit Assembly
Power Supply Assembly (1of 3)
Step 1
9-Volt battery clip
Notch up
Gather these components (parts).
U2
D2
DIP Socket
Step 2
Switch
Insert socket at location U1,
notch end up. All eight pins
must pass through the holes.
Printed Circuit Board (PCB)
C2
C3
Step 3
Tape socket flat to board to
prepare for soldering.
Step 4
Solder the socket into place.
Step 5
Thread battery clip wires
through center holes as
shown. Red lead closer to
center of board.
Step 6
Poke bare ends of wires up
through B+ and B- holes.
Bend bare leads outward to
prepare for soldering.
Power Supply Assembly (2 of 3)
Step 7
Pull center wires up until small loops
remain as shown. Make sure that all
of the bare wire extends up through the
holes.
Step 8
Solder the bare leads on the topside
of the board. Clip wires close above
solder joints.
Step 9
Pull remaining wire through board.
Only insulated wire should pass
through center holes.
Step 10
Place switch onto the circuit
board as shown.
Step 11
Tape the switch flat to board
to prepare for soldering.
Step 12
Solder all eight switch
pins into place.
Power Supply Assembly (3 of 3)
Step 13
Insert U2 as shown. Push into board
deep enough so that wire leads are below
top of switch.
Flat side faces this way.
U2
Top of switch
Leads
Step 20
Solder into place and clip the leads
close the solder joint.
Step 15
Install two blue capacitors, C2 and C3.
C2 and C3 are Polarized. White
stripes face the outside edge of board.
White stripes.
Step 19
Push capacitors tight to board and bend
leads. Solder in place and clip leads
above solder joint.
D2
Black band lines up with
white band on the board.
Step 17
Bend the leads on D2 diode and insert
into board as shown. Diode is
polarized. See note to the left.
Step 18
Bend, solder and clip leads close to
board.
Power Supply Testing (1of 2)
Short Circuit Test
1)
2)
3)
4)
5)
6)
7)
8)
9-Volt Battery Test
1)
2)
3)
4)
Set the meter to the VDC setting (Volts DC).
touch the red meter lead to the positive (+) battery
terminal and the black lead to the negative (-)
terminal.
A fully charged 9-Volt battery should read between
9 and 10 volts.
Reversing the leads should indicate a negative
voltage of the same value. Why?
Slide the CricketSat power switch to the ON
position.
Set the multimeter to the Ohms setting.
Touch the meter leads to the terminals of the
battery clip as shown.
Wait a few seconds for reading to stabilize.
Meter should display O.L or O.F for overflow.
Reverse the leads and repeat the test
If meter indicates a near-zero reading, check for
solder shorts or incorrectly installed components.
Do not connect the battery to the CricketSat until
the short circuit has been resolved.
Power Supply Testing (2 of 2)
9-Volt (V+) Test
1)
2)
3)
4)
5)
Test Points
5-Volt Regulator Test
1)
2)
3)
4)
5)
Now touch the red meter lead to the 5V test point
directly below the V+ test point.
The meter should display around 5 Volts. This
voltage is derived from U2, a 5-Volt regulator.
It has an accuracy of 4.75 to 5.25 volts. Everything
is fine if your measurement is in this range.
If the voltage is out of this range, check to make sure
that U2 is oriented with the flat face towards the left.
Also, check that the negative end (white stripes) of
the capacitors C2 and C3 face the top of the board.
Connect the battery to the CricketSat. Make sure
the switch is in the ON position.
Set the multimeter to the VDC setting.
Touch the meter leads to the GND and V+ test
points on the CricketSat board as shown to the left.
The meter should indicate nearly 9 volts for a fully
charged battery.
If the voltage is absent, check to make sure that
nearby diode D2 is installed with the black band
oriented to the left..
Oscillator Circuit Assembly
Before Proceeding
1. Turn off power to the CricketSat
2. Disconnect the battery
3. Wear safety glasses
Oscillator Assembly (1of 2)
C1
D1
C4 C5
Step 1
Gather these parts.
R1
U1
R2
R3
R4
Step 2
Bend the resistor leads
at right angles to the
Step 3
body.
Install the three resistors
(R2, R3, and R4). Bend,
solder and clip the leads.
Resistors are not polarized.
Orientation does not matter.
Step 4
Install the yellow
capacitors, C4 and C5.
Bend, solder and clip the
leads.
Longer lead (+)
These capacitors are not polarized.
Orientation does not matter.
Step 5
Install the LED at location
D1. The device is Polarized.
The longer lead is positive.
Oscillator Assembly (2 of 2)
Step 6
R1
Install the thermistor
R1 as shown. Solder
and clip the leads.
Step 7
Press the timer IC,
U1, into the socket.
Pin 1 up towards
notch in socket.
Notch
Dimple
Pin 1
Dimple
U1
C1
White stripe
Step 8
Install capacitor C1.
Capacitor is polarized.
Orient C1 with white
stripe as shown.
Oscillator Testing (1 of 3)
Flashing LED
1)
2)
3)
4)
Frequency Measurement
1)
2)
3)
4)
5)
6)
This measurement can only be made by a
multimeter that can measure frequency.
Set the meter to the frequency measurement setting,
Hertz (Hz).
Touch the red meter lead to the OUT test point.
Touch the black meter lead to the GND test point.
The meter will indicate the frequency in Hertz.
One Hertz = 1 cycle per second or in our case,
flash per second.
Connect the 9-Volt battery.
Slide the CricketSat power switch to the ON
position.
Observe the red or green LED.
It should be flashing on and off about once or twice
per second.
Oscillator Testing (2 of 3)
Timing Capacitor Waveform
Oscilloscope test probe
1)
2)
3)
4)
5)
6)
7)
This procedure allows the signal on the timing
capacitor to be viewed on an oscilloscope.
Turn ON the CricketSat circuit board.
Connect the oscilloscope ground lead to one of the
four corner holes in the CricketSat board. These
are connected to the ground (GND) wiring plane.
Touch the oscilloscope probe to the VC1 test point.
Adjust the gain of the oscilloscope to observe a
rising and falling voltage signal.
The LED should be OFF while the voltage is rising,
and ON while it is falling..
Animation to the left demonstrates analog signal
waveform.
Oscillator Testing (3 of 3)
Digital Output Waveform
Oscilloscope test probe
1)
2)
3)
4)
5)
6)
7)
This procedure allows the signal on the timing
capacitor to be viewed on an oscilloscope.
Turn ON the CricketSat circuit board.
Connect the oscilloscope ground lead to one of the
four corner holes in the CricketSat board. These
are connected to the ground (GND) wiring plane.
Touch the oscilloscope probe to the OUT test point.
Adjust the gain of the oscilloscope to observe a
rising and falling voltage signal.
The LED should be OFF while the voltage is rising,
and ON while it is falling..
Animation to the left demonstrates digital output
waveform.
Transmitter Circuit Assembly
Before Proceeding
1. Turn off power to the CricketSat
2. Disconnect the battery
3. Wear safety glasses
Transmitter Assembly (1)
Step 1
Gather these remaining parts.
Antenna Wires
U3
Step 2
C6
Bend the bare ends of the antenna
wires at a right angle.
Step 3
Insert bare wire ends from the
back side of board. Use masking
tape to hold in place.
Use outer holes.
Step 4
Solder and trim exposed wires.
Step 5
Route free ends of antenna wires
up through the center holes.
Step 6
Pull remaining wire tightly through
board. (See following photos for
final antenna detail.)
Transmitter Assembly (2)
Step 7
Install capacitor C6. Bend, solder
and clip the leads.
Step 8
Install the RF transmitter module
U3, facing the metal can towards the
antenna as shown.
Step 9
Bend, solder and clip the
transmitter’s leads.
Final Inspection
White bands up
Dimple on IC
Black band
Flat face
Wire clipped
close to board
Metal can facing outward
Insulation through holes.
Insulation through holes.
All component leads clipped short
Final Assembly
1)
2)
3)
4)
Turn off power switch
Connect snap connector to battery terminals
Affix battery to bottom of CricketSat using the
Velcro
Secure the connection with a plastic tie-wrap
as shown above
Wireless Testing
Preparing the CricketSat
1)
2)
3)
Turn on the power switch
The CricketSat should transmit around 433.92
MHz.
It may be as low as 433.75 or as high as 434.25
MHz
Testing
1)
2)
3)
4)
5)
Use an amateur radio transceiver such as the
Kenwood THD-7A or a low-cost UHF receiver
similar to the UVM CricketSat unit shown right
Turn the receiver unit on, and tune through the
frequency range specified above listening for
the clicks
Adjust the volume as needed
For the UVM CricketSat receiver, just turn the
unit on and adjust the volume
Red LED should also flash if CricketSat is
nearby