1. UVM CricketSat Manual

2. What’s a CricketSat? Operation Description
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
Description
Wireless temperature sensor
Usually flown on a balloon
Simple circuit
Easy to build
Easy to modify
Low cost (~$10)

3. 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)

4. 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
Test bed for CubeSat
CubeSat
Earth-orbit satellite

5. 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

6. CricketSat Schematic Diagram
Power Supply
Transmitter
Temperature Sensitive Oscillator

7. CricketSat Circuit Board
Custom Circuit Prototype Area
Transmitter
Oscillator
Power Supply

8. 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

9. 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

10. 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

11. 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

12. Detail Operation – Power Supply

13. Power Supply Operation
9 Volts unregulated supply
Max power to RF transmitter for maximum range.
5.0 Volts regulated supply
5-Volt regulator (U2), 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.

14. Detail Operation - Oscillator

15. Oscillator Demo 555 Timer IC Voltage on capacitor C1 LED Vcc Time
Thermistor R1
555 Timer IC
Vcc
LED R2
Digital Output Signal
Voltage on capacitor C1
Not Used C1
Capacitor Charge & Discharge Waveform
Time
Simulation courtesy of Williamson Labs:

16. 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:

17. 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.

18. 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.

19. Detail Operation – Transmitter
Power Supply
Transmitter
Temperature Sensitive Oscillator

20. 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,

21. Assembly Equipment List
Assembly and Repair
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

22. Assembly Preparation Safety Follow the directions
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.

23. Non-Polarized Components
R4: 100 Ohm C4 C5 C6
Negative White Band
Non-Polarized Components
Brown-Black-Brown-Gold
0.1 micro-Farad Capacitors
R2: 3300 Ohm
Orange-Orange-Red-Gold
Black Band
D2 - Diode + - + - + - - +
Longer Lead
R3: 680 Ohm
47 micro-Farad Electrolytic Capacitors
Notch
Dimple
Blue-Gray-Brown-Gold
Pin 1
1234
8765
U3: RF Transmitter D1
DIP Socket
U1: 555 Timer IC R1 U2
SW1
Flat Side Up
Longer Lead
Pins:
1 2 3
Pins:
On/Off Switch
10K Ohm Thermistor - +
5-Volt Regulator
Light Emitting Diode (LED)
Velcro
B1: 9-Volt Battery
Printed Circuit Board (PCB) - +
Red Lead is Positive
Battery Snap Connector
Antenna Wires - +

24. Printed Circuit Board Purpose Composition Front side of board
To provide mechanical support and electrical connectivity for components.
Composition
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
Install components on this side of board.
White silkscreen
Component placement outlines.
Reference designators to associate components to schematic diagram.
Back side of board
Most of the soldering is done on this side of the circuit board.

25. Assembly Techniques Inserting Devices Soldering Snipping leads
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.
45 degree angle is best
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
Use safety glasses to protect your eyes.
Hold lead while cutting or point downward.
Snip just above solder joint

26. Power Supply Circuit Assembly

27. Power Supply Assembly (1of 3)
Step 1
Notch up
9-Volt battery clip
Gather these components (parts). U2
Step 2 D2
DIP Socket
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.

28. 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.

29. 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.
Step 17 D2
Bend the leads on D2 diode and insert into board as shown. Diode is polarized. See note to the left.
Black band lines up with white band on the board.
Step 18
Bend, solder and clip leads close to board.

30. Power Supply Testing (1of 2)
Short Circuit Test
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.
9-Volt Battery Test
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?

31. Power Supply Testing (2 of 2)
9-Volt (V+) Test
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..
Test Points
5-Volt Regulator Test
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 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.

32. Oscillator Circuit Assembly

33. Before Proceeding Turn off power to the CricketSat
Disconnect the battery
Wear safety glasses

34. Oscillator Assembly (1of 2)D1
Step 1
C4 C5
Gather these parts. R1
Step 2 U1
Bend the resistor leads at right angles to the body. R2 R3
Step 3 R4
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.

35. 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
Step 8
Install capacitor C1. Capacitor is polarized. Orient C1 with white stripe as shown.
White stripe

36. Oscillator Testing (1 of 3)
Flashing LED
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.
Frequency Measurement
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.

37. Oscillator Testing (2 of 3)
Timing Capacitor Waveform
Oscilloscope test probe
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.

38. Oscillator Testing (3 of 3)
Digital Output Waveform
Oscilloscope test probe
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.

39. Transmitter Circuit Assembly

40. Before Proceeding Turn off power to the CricketSat
Disconnect the battery
Wear safety glasses

41. Transmitter Assembly (1)
Step 1
Gather these remaining parts.
Antenna Wires
Step 2 C6 U3
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.)

42. 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.

43. Final Inspection White bands up Flat face Black band Dimple on IC
Wire clipped close to board
Metal can facing outward
Insulation through holes.
Insulation through holes.
All component leads clipped short

44. Final Assembly 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

45. Preparing the CricketSat
Wireless Testing
Preparing the CricketSat
Turn on the power switch
The CricketSat should transmit around MHz.
It may be as low as or as high as MHz
Testing
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