2 What’s a CricketSat? Operation Description Produces tone or pulses related to changing temperatureTransmits the tone wirelessly over a radio frequency (RF) linkReceived tone frequency measured with an instrument or computer softwareCalibration graph used to convert tone frequency back to temperatureDescriptionWireless temperature sensorUsually flown on a balloonSimple circuitEasy to buildEasy to modifyLow cost (~$10)
3 The CricketSat Program at UVM Freshman introduction to engineeringSensor and system developmentHELiX / EPSCoR High School Outreach program2003: Waldorf High School, VT2004: Milton, VT and JDOB Boston, MA2005: Milton and Brattleboro, VTUniversity collaborationMedgar Evers College, City University of New YorkUniversity of AlaskaAwards (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 OriginsDeveloped at Stanford UniversitySpace Systems Development LaboratoryPart of the NASA student satellite programCrawl, Walk, Run, FlyTeach fundamentals of space hardware developmentSpace Grant Fellowship ProgramFunded supportVermont Space Grant Consortium (VSGC)Student Satellite ProgramsCricketSatLowest cost - disposableLive telemetryBalloonSatLarger balloonExpensive instrumentsGPS tracking systemCanSatDropped by parachute from plane or rocketMany instrumentsTest bed for CubeSatCubeSatEarth-orbit satellite
5 CricketSat Sensor Circuit Oscillator frequency determined by temperatureOscillator output signal modulates RF carrier frequencyReceiving StationReceiver extracts oscillator frequency from radio signalOscillator frequency measured by instruments or softwareCalibration charts used to determine temperature
6 CricketSat Schematic Diagram Power SupplyTransmitterTemperature Sensitive Oscillator
8 Sensing the Temperature Thermistor DeviceResistance changes with temperature as shown in the graphRequires additional circuitry to produce an measurable electrical responseUse with an oscillator circuit provides a simple and low cost solutionThermistor
9 Temperature Sensitive Oscillator ThermistorProduces an oscillation that changes with temperatureCircuit based on the popular 555-Timer ICOscillator frequency determined by two resistors and a capacitorResistive and capacitive type sensors may be substitutedIn our case, the upper resistor is replaced with the thermistorChanges in temperature affect the oscillator frequency as shown in the chart
10 Frequency vs Temperature Oscillator FrequencyIncreases with warmer temperaturesDecreases with colder temperaturesFinding the TemperatureA 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 cycleOscillator frequency is mixed with radio (RF) carrier frequency to provide the wireless connection
13 Power Supply Operation 9 Volts unregulated supplyMax power to RF transmitter for maximum range.5.0 Volts regulated supply5-Volt regulator (U2), Volts input, 5.0 Volts outputProvides constant output as battery discharges (dies).Required by oscillator circuit for consistent operation.May be required for student-added circuity.Short-circuit protectionPrevents damage with reverse battery connection.5-Volt regulator has built-in protection.Diode D2 added to protect RF transmitter module.
15 Oscillator Demo 555 Timer IC Voltage on capacitor C1 LED Vcc Time ThermistorR1555 Timer ICVccLEDR2Digital Output SignalVoltage on capacitor C1Not UsedC1Capacitor Charge & Discharge WaveformTimeSimulation courtesy of Williamson Labs:
16 Oscillator Circuit Operation Based on the popular 555 timer IC design.Timing componentsCapacitor 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 operationVoltage level on C1 oscillates between 1/3 and 2/3 of the supply voltage (5 Volts).Charging intervalVoltage 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 intervalThe 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 OutputThe 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 RelationshipThe 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 SupplyTransmitterTemperature Sensitive Oscillator
20 RF Transmitter Operation PurposeModulate (mix) 434 MHz “carrier” signal and 555-Timer output signalAmplify and transmit signal through antenna sized for 434 MHzCommon Types of ModulationFM: Frequency ModulationPM: Phase ModulationAM: Amplitude ModulationAnalogEx: AudioDigital (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 RepairSoldering 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.TestingDigital multi-meterOscilloscope (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 directionsThere 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 orientationMany 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 componentsThe components outlined in Blue on the following page are not polarized, and may be installed in either direction.OrganizationMake 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.
24 Printed Circuit Board Purpose Composition Front side of board To provide mechanical support and electrical connectivity for components.CompositionCircuit 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 layersGreen insulating layer covers metal, except at pads and holes.Front side of boardInstall components on this side of board.White silkscreenComponent placement outlines.Reference designators to associate components to schematic diagram.Back side of boardMost 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 bestSolderingSoldering 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 boardSnipping leadsUse safety glasses to protect your eyes.Hold lead while cutting or point downward.Snip just above solder joint
27 Power Supply Assembly (1of 3) Step 1Notch up9-Volt battery clipGather these components (parts).U2Step 2D2DIP SocketSwitchInsert socket at location U1, notch end up. All eight pins must pass through the holes.Printed Circuit Board (PCB)C2C3Step 3Tape socket flat to board to prepare for soldering.Step 4Solder the socket into place.Step 5Thread battery clip wires through center holes as shown. Red lead closer to center of board.Step 6Poke 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 7Pull center wires up until small loops remain as shown. Make sure that all of the bare wire extends up through the holes.Step 8Solder the bare leads on the topside of the board. Clip wires close above solder joints.Step 9Pull remaining wire through board. Only insulated wire should pass through center holes.Step 10Place switch onto the circuit board as shown.Step 11Tape the switch flat to board to prepare for soldering.Step 12Solder all eight switch pins into place.
29 Power Supply Assembly (3 of 3) Step 13Insert U2 as shown. Push into board deep enough so that wire leads are below top of switch.Flat side faces this way.U2Top of switchLeadsStep 20Solder into place and clip the leads close the solder joint.Step 15Install two blue capacitors, C2 and C3. C2 and C3 are Polarized. White stripes face the outside edge of board.White stripes.Step 19Push capacitors tight to board and bend leads. Solder in place and clip leads above solder joint.Step 17D2Bend 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 18Bend, solder and clip leads close to board.
30 Power Supply Testing (1of 2) Short Circuit TestSlide 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 testIf 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 TestSet 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+) TestConnect 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 Points5-Volt Regulator TestNow 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.
33 Before Proceeding Turn off power to the CricketSat Disconnect the batteryWear safety glasses
34 Oscillator Assembly (1of 2) D1Step 1C4 C5Gather these parts.R1Step 2U1Bend the resistor leads at right angles to the body.R2R3Step 3R4Install the three resistors (R2, R3, and R4). Bend, solder and clip the leads.Resistors are not polarized. Orientation does not matter.Step 4Install the yellow capacitors, C4 and C5. Bend, solder and clip the leads.Longer lead (+)These capacitors are not polarized. Orientation does not matter.Step 5Install the LED at location D1. The device is Polarized. The longer lead is positive.
35 Oscillator Assembly (2 of 2) Step 6R1Install the thermistor R1 as shown. Solder and clip the leads.Step 7Press the timer IC, U1, into the socket. Pin 1 up towards notch in socket.NotchDimplePin 1DimpleU1C1Step 8Install capacitor C1. Capacitor is polarized. Orient C1 with white stripe as shown.White stripe
36 Oscillator Testing (1 of 3) Flashing LEDConnect 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 MeasurementThis 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 WaveformOscilloscope test probeThis 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 WaveformOscilloscope test probeThis 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.
40 Before Proceeding Turn off power to the CricketSat Disconnect the batteryWear safety glasses
41 Transmitter Assembly (1) Step 1Gather these remaining parts.Antenna WiresStep 2C6U3Bend the bare ends of the antenna wires at a right angle.Step 3Insert bare wire ends from the back side of board. Use masking tape to hold in place.Use outer holes.Step 4Solder and trim exposed wires.Step 5Route free ends of antenna wires up through the center holes.Step 6Pull remaining wire tightly through board. (See following photos for final antenna detail.)
42 Transmitter Assembly (2) Step 7Install capacitor C6. Bend, solder and clip the leads.Step 8Install the RF transmitter module U3, facing the metal can towards the antenna as shown.Step 9Bend, solder and clip the transmitter’s leads.
43 Final Inspection White bands up Flat face Black band Dimple on IC Wire clipped close to boardMetal can facing outwardInsulation through holes.Insulation through holes.All component leads clipped short
44 Final Assembly Turn off power switch Connect snap connector to battery terminalsAffix battery to bottom of CricketSat using the VelcroSecure the connection with a plastic tie-wrap as shown above
45 Preparing the CricketSat Wireless TestingPreparing the CricketSatTurn on the power switchThe CricketSat should transmit around MHz.It may be as low as or as high as MHzTestingUse an amateur radio transceiver such as the Kenwood THD-7A or a low-cost UHF receiver similar to the UVM CricketSat unit shown rightTurn the receiver unit on, and tune through the frequency range specified above listening for the clicksAdjust the volume as neededFor the UVM CricketSat receiver, just turn the unit on and adjust the volumeRed LED should also flash if CricketSat is nearby