uvm cricketsat wireless sensor
DESCRIPTION
UVM CricketSat Wireless Sensor. Remote Temperature Measurement. Possible Application Measure temperature in the upper atmosphere 10 km altitude Two challenges: Measure temperature indirectly Long-range wireless transmission of data. Thermistor Temperature Sensor. - PowerPoint PPT PresentationTRANSCRIPT
UVM CricketSat Wireless Sensor
Remote Temperature Measurement
• Possible Application
– Measure temperature in the upper atmosphere
– 10 km altitude
• Two challenges:
– Measure temperature indirectly
– Long-range wireless transmission of data
Thermistor Temperature Sensor• Resistance changes with
temperature• Problem: Resistance
cannot be measured directly
• Requires additional circuitry to produce an electrical response
• Oscillator circuit is the simplest and lowest cost solution
• Produces an oscillation that changes with temperature
• Circuit based on the popular 555-Timer IC
• 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 a thermistor
Temperature Sensitive Oscillator
555-Timer Oscillator Demo
Click on picture for online demo
Frequency vs Temperature
• Thermistor resistance increases with colder temperature, reducing charging current
• Charging time increases, reducing the frequency
The Wireless Connection
• Timer output signal enables transmitter during charging interval of the timing cycle
• Oscillator frequency is mixed with RF carrier frequency• Antenna is sized for carrier frequency -> short
Receiving Station
• Receiver extracts oscillator frequency
• Frequency measured by instrument or software
• Calibration charts used to determine temperature
CricketSat Sensor
•Oscillator frequency determined by temperature
•Oscillator output signal modulates RF carrier frequency
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 D1 - 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-Orange-Gold
Blue-Gray-Brown-Gold
Completed CricketSat
Prototype Development
Area
Thermistor
Test Points
Dipole Antenna
RF Transmitter
Module
Timing Capacitor
5-Volt Regulator
IC
555 Timer
IC
Flashing LED
9-Volt Battery Leads
Timing Resistor
Primary Features
Output Jack
Noise Decoupling Capacitor
Series Isolation Resistor
Current Limiting Resistor (LED)
Noise Decoupling Capacitor
Protection Diode (Reverse Battery
Connection)
Noise Decoupling Capacitors
Secondary Features