1. UVM CricketSat Wireless Sensor

2. 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

3. 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

4. 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

5. 555-Timer Oscillator Demo Click on picture for online demo

6. Frequency vs Temperature Thermistor resistance increases with colder temperature, reducing charging current Charging time increases, reducing the frequency

7. 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

8. 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

10. C1C3C2 C4C5C6 U2 R1 D1 DIP Socket Notch U1: 555 Timer IC Dimple Pin 1 Flat Side Up 1 2 3 1 2 3 4 87658765 12341234 U3: RF Transmitter 5-Volt Regulator 10K Ohm Thermistor Printed Circuit Board (PCB) 47 micro-Farad Electrolytic Capacitors Longer Lead +-+-+- + - Light Emitting Diode (LED) 0.1 micro-Farad Capacitors + - Black BandD1 - Diode + - B1: 9-Volt Battery 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

11. Completed CricketSat

12. 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

13. 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