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What is that little black arachnid that was in your baggie?

What is that little black arachnid that was in your baggie?. IC 555. I can calculate the charging and discharging time for a capacitor. I can calculate the period and frequency for a 555 Timer Oscillator .

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What is that little black arachnid that was in your baggie?

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  1. What is that little black arachnid that was in your baggie? IC 555

  2. IC 555 • I can calculate the charging and discharging time for a capacitor. • I can calculate the period and frequency for a 555 Timer Oscillator. • I can describe how the 555 Timer Oscillator can be used to produce temperature information. IC 555

  3. What is the IC 555? The IC 555 is an 8-pin Integrated Circuit (IC) that is capable of producing accurate time delays and/or oscillations. DIP chip (Dual-Inline package) IC 555

  4. IC 555 – Why 555? Vcc (8) Discharge (7) 5 kΩ T1 Control Voltage (5) Comparator 1 Flip-Flop - + Threshold Voltage (6) 5 kΩ RESET Q Output (3) Comparator 2 Trigger Voltage (2) - + SET Q 5 kΩ Ground (1) Reset (4) IC 555 4

  5. IC 555 timer Time Delay Mode Oscillator Mode In the oscillator mode, the frequency of oscillation are controlled with two external resistors and one capacitor. Example: Can make a light flash a specific rate.(Can turn on and off repeatedly) • In the time delay mode, the delay is controlled by one external resistor and capacitor. Example: Turn a light on in a delayed amount of time.(Just turn on or off once) This presentation will discuss how to use a 555 timer in the oscillator mode. IC 555

  6. IC 555 timer Oscillator mode = astablemultivibrator mode Translation: in this mode the IC 555 will continue to put out pulses until you remove the battery. (your choice of resistors and capacitors determines the vibration frequency) The 555 timer is a two state device: HI and LOYou can be a two state device too…… IC 555

  7. IC 555 timer Astablemultivibrator mode schematic Notice: 2 resistors and 1 capacitorOUTPUT is square wave pulsesLESSON 15 “How the 555 Timer Works” IC 555

  8. Thermistors What do you predict will happen to the resistance of the thermistor as it ascends into the atmosphere? Temperature dependent Resistors R = resistance T = temperature k = temperature coefficient Two types of Thermistors k = positive (PTC) K = negative (NTC) Our resistor is an NTC thermistor with a range of 10 kΩ – 80 kΩ IC 555

  9. Experiment a bit Experiment by using the Thermistor in place of R2. You may use the spray coolant to cool the thermistor – but be careful it can get super cold! • How does reducing the temperature of the thermistor change the output of the IC 555 timer? • What evidence do you have to support this? IC 555

  10. NTC thermistor IC 555

  11. Output = High tHIGH : Calculations for the Oscillator’s HIGH Time The Output Is HIGH While The Capacitor Is Charging Through RA + RB. IC 555

  12. Output = Low tLOW : Calculations for the Oscillator’s LOW Time The Output Is LOW While The Capacitor Is Discharging Through RB. IC 555

  13. IC 555 timer Visit this link to view a simulation of the IC 555 in astable mode http://www.williamson-labs.com/pu-aa-555-timer_slow.htm How does the charge and discharge of the capacitor relate to the blinking LED? IC 555

  14. Period The Period is the total time of an on/off cycle and depends on the values of RA, RB, and C Calculate the period of the flashing light. IC 555

  15. Frequency The frequency of an oscillation (or anything that exhibits a repeating pattern) is inversely proportional to the period Unit of Measure: cycles/second = Hertz (Hz) • Calculate the frequency (or blinking rate) of the flashing light. IC 555

  16. Practice Calculate the period and frequency of the blinking LED. μ = 10-6 IC 555

  17. Solution Period Frequency IC 555

  18. Practice Calculate the period and frequency of the blinking light assuming the resistance in the frequency is 10 kΩ. Assume Elsa from frozen just walked in and room temperature just dropped to 0 ̊C and the resistance on the thermistor is 30 kΩ. PREDICT – will the light blink faster or slower? Calculate the period and frequency of the blinking light now. IC 555

  19. CricketSat Schematic IC 555

  20. Key Points The 555 timer works with 2 resistors (one of which is temperature dependent) and 1 capacitor to establish an oscillation in the circuit. The 555 timer output has two modes: ON and OFF and it turns whatever device it is connected to ON and OFF at a rate that depends on the changing resistance of the thermistor (which depends on temperature)!!! IC 555

  21. IC 555

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