1. Monday July 14, 2014IC 5551 What is that little black arachnid that was in your baggie?

2. IC 555 Monday July 14, 2014IC 5552 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.

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. Monday July 14, 2014IC 5553 DIP chip (Dual-Inline package)

4. IC 555 – Why 555? Monday July 14, 2014IC 5554 Control Voltage (5) Trigger Voltage (2) Ground (1) Vcc (8)Discharge (7) Reset (4) Output (3) -+-+ -+-+ RESET SET Q Q Comparator 1 Comparator 2 Flip-Flop T1 4 Threshold Voltage (6) 5 kΩ

5. IC 555 timer Time Delay Mode 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) 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) Monday July 14, 2014IC 5555 This presentation will discuss how to use a 555 timer in the oscillator mode.

6. IC 555 timer Monday July 14, 2014IC 5556 Oscillator mode = astable multivibrator 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 LO You can be a two state device too……

7. IC 555 timer Astable multivibrator mode schematic Notice: 2 resistors and 1 capacitor OUTPUT is square wave pulses LESSON 15 “How the 555 Timer Works” Monday July 14, 2014IC 5557

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 Monday July 14, 2014IC 5558

9. Experiment a bit Monday July 14, 2014IC 5559 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! 1.How does reducing the temperature of the thermistor change the output of the IC 555 timer? 2.What evidence do you have to support this?

10. NTC thermistor Monday July 14, 2014IC 55510

11. Output = High Monday July 14, 2014IC 55511 t HIGH : Calculations for the Oscillator’s HIGH Time T HE O UTPUT I S HIGH W HILE T HE C APACITOR I S C HARGING T HROUGH R A + R B.

12. 12 t LOW : Calculations for the Oscillator’s LOW Time 5v 3.333 v VcVc 1.666 v 0 v  t LOW  Output HIGH LOW T HE O UTPUT I S LOW W HILE T HE C APACITOR I S D ISCHARGING T HROUGH R B. Output = Low Monday July 14, 2014IC 555

13. IC 555 timer Monday July 14, 2014IC 55513 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?

14. Period The Period is the total time of an on/off cycle and depends on the values of RA, RB, and C Monday July 14, 2014IC 55514 Calculate the period of the flashing light.

15. Frequency The frequency of an oscillation (or anything that exhibits a repeating pattern) is inversely proportional to the period Monday July 14, 2014IC 55515 Calculate the frequency (or blinking rate) of the flashing light. Unit of Measure: cycles/second = Hertz (Hz)

16. Practice Calculate the period and frequency of the blinking LED. Monday July 14, 2014IC 55516 μ = 10 -6

17. Solution PeriodFrequency Monday July 14, 2014IC 55517

18. Practice Monday July 14, 2014IC 55518 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.

19. CricketSat Schematic Monday July 14, 2014IC 55519

20. Key Points Monday July 14, 2014IC 55520 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)!!!

21. Monday July 14, 2014IC 55521