UVM CricketSat Manual

What’s a CricketSat?Description

• Wireless temperature sensor

• Usually flown on a balloon

• Simple circuit– Easy to build– Easy to modify

• Low cost (~$10)

Operation• 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

Receiving Station• Receiver extracts oscillator

frequency from radio signal• Oscillator frequency measured

by instruments or software• Calibration charts used to

determine temperature

CricketSat Sensor Circuit • Oscillator frequency

determined by temperature• Oscillator output signal

modulates RF carrier frequency

CricketSat Schematic Diagram

Power Supply Transmitter Temperature Sensitive Oscillator

CricketSat Circuit Board

Power SupplyTransmitter Oscillator

Custom Circuit Prototype Area

Sensing the TemperatureThermistor 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

• 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

Thermistor

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– 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

Capacitor Charge & Discharge Waveform

LED

Digital Output Signal

555 Timer IC

Time

Not Used

R1

R2

C1

Thermistor

Vcc

Vol

tage

on

cap

acit

or C

1

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:

121 2

44.1)( CRRHzf

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

– 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• 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 C3C2C4 C5 C6

U2R1

D1DIP

Socket

Notch

U1: 555 Timer

IC

Dimple

Pin 1

Flat Side Up

1 2 31 2 3 4

8765

1234

U3: RF Transmitter

5-Volt Regulator

10K Ohm Thermistor

Printed Circuit Board (PCB)

47 micro-Farad Electrolytic Capacitors

Longer Lead

+ - + - + -

Longer Lead+-

Light Emitting

Diode (LED)

0.1 micro-Farad Capacitors

+-

Black Band D2 - Diode

+-

B1: 9-Volt Battery

Pins: Pins:

Antenna Wires

Battery Snap Connector

+

-

Red Lead is Positive

R4: 100 Ohm

R2: 3300 Ohm

R3: 680 Ohm

Brown-Black-Brown-Gold

Orange-Orange-Red-Gold

Blue-Gray-Brown-Gold

Negative White Band

On/Off Switch

SW1

Velcro

Non-Polarized Components

Printed Circuit Board

• 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.

• Purpose– To provide mechanical support and

electrical connectivity for components.

Assembly Techniques• Inserting Devices

– 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– 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 ™.

• Snipping leads– Use safety glasses to protect your eyes.

– Hold lead while cutting or point downward.

Bend lead close to board

45 degree angle is best

Snip just above solder joint

Power Supply Circuit Assembly

Power Supply Assembly (1of 3)Gather these components (parts).

Insert socket at location U1, notch end up. All eight pins must pass through the holes.

Solder the socket into place.

Tape socket flat to board to prepare for soldering.

Notch up

Thread battery clip wires through center holes as shown. Red lead closer to center of board.

Poke bare ends of wires up through B+ and B- holes.

Bend bare leads outward to prepare for soldering.

D2

Printed Circuit Board (PCB)

9-Volt battery clip

U2

DIP Socket

C2

C3

Switch

Step 1

Step 2

Step 3

Step 5

Step 4

Step 6

Power Supply Assembly (2 of 3)Pull center wires up until small loops remain as shown. Make sure that all of the bare wire extends up through the holes.

Solder the bare leads on the topside of the board. Clip wires close above

solder joints.

Place switch onto the circuit board as shown.

Pull remaining wire through board. Only insulated wire should pass through center holes.

Tape the switch flat to board to prepare for soldering.

Solder all eight switch pins into place.

Step 7

Step 8

Step 9

Step 10

Step 11

Step 12

Power Supply Assembly (3 of 3)Insert U2 as shown. Push into board deep enough so that wire leads are below top of switch.

Solder into place and clip the leads close the solder joint.

Push capacitors tight to board and bend leads. Solder in place and clip leads

above solder joint.

Install two blue capacitors, C2 and C3. C2 and C3 are Polarized. White stripes face the outside edge of board.

Bend the leads on D2 diode and insert into board as shown. Diode is polarized. See note to the left.

Bend, solder and clip leads close to board.

Leads

Top of switch

Flat side faces this way.

White stripes.

Black band lines up with white band on the board.

D2

U2

Step 13

Step 15

Step 17

Step 20

Step 19

Step 18

Power Supply Testing (1of 2)

1) Slide the CricketSat power switch to the ON position.

2) Set the multimeter to the Ohms setting.3) Touch the meter leads to the terminals of the

battery clip as shown.4) Wait a few seconds for reading to stabilize.5) Meter should display O.L or O.F for overflow.6) Reverse the leads and repeat the test7) If meter indicates a near-zero reading, check for

solder shorts or incorrectly installed components.8) Do not connect the battery to the CricketSat until

the short circuit has been resolved.

Short Circuit Test

1) Set the meter to the VDC setting (Volts DC).2) touch the red meter lead to the positive (+) battery

terminal and the black lead to the negative (-) terminal.

3) A fully charged 9-Volt battery should read between 9 and 10 volts.

4) Reversing the leads should indicate a negative voltage of the same value. Why?

9-Volt Battery Test

Power Supply Testing (2 of 2)

1) Connect the battery to the CricketSat. Make sure the switch is in the ON position.

2) Set the multimeter to the VDC setting.3) Touch the meter leads to the GND and V+ test

points on the CricketSat board as shown to the left.4) The meter should indicate nearly 9 volts for a fully

charged battery.5) If the voltage is absent, check to make sure that

nearby diode D2 is installed with the black band oriented to the left..

9-Volt (V+) Test

1) Now touch the red meter lead to the 5V test point directly below the V+ test point.

2) The meter should display around 5 Volts. This voltage is derived from U2, a 5-Volt regulator.

3) It has an accuracy of 4.75 to 5.25 volts. Everything is fine if your measurement is in this range.

4) If the voltage is out of this range, check to make sure that U2 is oriented with the flat face towards the left.

5) Also, check that the negative end (white stripes) of the capacitors C2 and C3 face the top of the board.

5-Volt Regulator Test

Test Points

Oscillator Circuit Assembly

Before Proceeding

1. Turn off power to the CricketSat

2. Disconnect the battery

3. Wear safety glasses

Oscillator Assembly (1of 2)

Gather these parts.

Install the three resistors (R2, R3, and R4). Bend, solder and clip the leads.

Install the LED at location D1. The device is Polarized.

The longer lead is positive.

Install the yellow capacitors, C4 and C5. Bend, solder and clip the leads.

Longer lead (+)

Resistors are not polarized. Orientation does not matter.

These capacitors are not polarized. Orientation does not matter.

U1

C4 C5

R1

D1

R2

R3

R4

C1 Step 1

Step 3

Step 4

Step 5

Bend the resistor leads at right angles to the body.

Step 2

Oscillator Assembly (2 of 2)

Install the thermistor R1 as shown. Solder and clip the leads.

Press the timer IC, U1, into the socket.

Pin 1 up towards notch in socket.

Pin 1

Dimple

U1

Notch

Dimple

Install capacitor C1. Capacitor is polarized. Orient C1 with white stripe as shown.

R1

C1

White stripe

Step 6

Step 7

Step 8

Oscillator Testing (1 of 3)

1) Connect the 9-Volt battery.2) Slide the CricketSat power switch to the ON

position.3) Observe the red or green LED.4) It should be flashing on and off about once or

twice per second.

Flashing LED

1) This measurement can only be made by a multimeter that can measure frequency.

2) Set the meter to the frequency measurement setting, Hertz (Hz).

3) Touch the red meter lead to the OUT test point.4) Touch the black meter lead to the GND test point.5) The meter will indicate the frequency in Hertz.6) One Hertz = 1 cycle per second or in our case,

flash per second.

Frequency Measurement

Oscillator Testing (2 of 3)

1) This procedure allows the signal on the timing capacitor to be viewed on an oscilloscope.

2) Turn ON the CricketSat circuit board. 3) 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.

4) Touch the oscilloscope probe to the VC1 test point.5) Adjust the gain of the oscilloscope to observe a

rising and falling voltage signal.6) The LED should be OFF while the voltage is

rising, and ON while it is falling..7) Animation to the left demonstrates analog signal

waveform.

Timing Capacitor WaveformOscilloscope test probe

Oscillator Testing (3 of 3)

1) This procedure allows the signal on the timing capacitor to be viewed on an oscilloscope.

2) Turn ON the CricketSat circuit board. 3) 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.

4) Touch the oscilloscope probe to the OUT test point.

5) Adjust the gain of the oscilloscope to observe a rising and falling voltage signal.

6) The LED should be OFF while the voltage is rising, and ON while it is falling..

7) Animation to the left demonstrates digital output waveform.

Digital Output WaveformOscilloscope test probe

Transmitter Circuit Assembly

Before Proceeding

1. Turn off power to the CricketSat

2. Disconnect the battery

3. Wear safety glasses

Transmitter Assembly (1)

C6U3

Gather these remaining parts.Step 1

Bend the bare ends of the antenna wires at a right angle.

Step 2

Antenna Wires

Insert bare wire ends from the back side of board. Use masking

tape to hold in place.

Step 3

Solder and trim exposed wires.Step 4

Use outer holes.

Route free ends of antenna wires up through the center holes.

Step 5

Pull remaining wire tightly through board. (See following photos for final antenna detail.)

Step 6

Transmitter Assembly (2)

Install capacitor C6. Bend, solder and clip the leads.

Step 7

Install the RF transmitter module U3, facing the metal can towards the

antenna as shown.

Step 8

Bend, solder and clip the transmitter’s leads.

Step 9

Final Inspection

Black band

All component leads clipped shortInsulation through holes.

Insulation through holes.

White bands up

Flat face

Wire clipped close to boardMetal can facing outward

Dimple on IC

Final Assembly

1) Turn off power switch2) Connect snap connector to battery terminals3) Affix battery to bottom of CricketSat using the

Velcro4) Secure the connection with a plastic tie-wrap

as shown above

Wireless Testing

1) Turn on the power switch2) The CricketSat should transmit around 433.92

MHz.3) It may be as low as 433.75 or as high as 434.25

MHz

Preparing the CricketSat

Testing

1) 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

2) Turn the receiver unit on, and tune through the frequency range specified above listening for the clicks

3) Adjust the volume as needed4) For the UVM CricketSat receiver, just turn the

unit on and adjust the volume5) Red LED should also flash if CricketSat is

nearby