2. Presented by Tim Surtell in association with
Kelsey Park School Electronics Club
Computer & Software Services Limited

3. Lecture Outline In this lecture we’ll look at… The ‘black box’ concept
Using the 555 timer IC
Three 555 timer circuits
Practical matters
After the break…
Hands-On session: Build your 555 monostable circuit

4. The ‘Black Box’ of Electronics
Power
Process
Input(s)
Output(s)

5. The Block Diagram
Input
Process 1
Process 2
Process 3
Output

6. The 555 Timer – A Black Box!
555 1 8 2 7 3 6 4 5
Eight connections called ‘pins’
Little white dot and dimple denote pin 1

7. The 555 Timer – A Black Box! 0V 1 8 Vs 2 7 555 3 6 4 5
The 555 uses a 3 – 18V DC power supply

8. The 555 Timer – A Black Box! 0V 1 8 Vs Trigger 2 7 555 3 6 Reset 4 5
The Trigger and Reset inputs

9. Switches Connecting a switch to the Trigger input: 1st attempt!0V
Switch
Trigger input

10. Switches Connecting a switch to the Trigger input: 2nd attempt! Vs
Bang!

11. Switches
Connecting a switch to the Trigger input of the 555 using a pull-up resistor Vs
1kΩ resistor 0V
Switch
Trigger input

12. The 555 Timer 0V 1 8 Vs Trigger 2 7 555 Output 3 6 Reset 4 5
The 555 Output

13. Lamps Connecting a lamp to the 555 Output by ‘sourcing’ current Output0V
Lamp
Output

14. Lamps Connecting a lamp to the 555 Output by ‘sinking’ current Vs

15. Light Emitting Diodes (LEDs)0V
LED
Output
Resistor R

16. Relays 0V
Diode
Output
Relay Coil Vs
Motor
Relay Switch M

17. The 555 Timer 0V 1 8 Vs Trigger 2 7 Discharge 555 Output 3 6 Threshold
Reset 4
5 Offset
Connections for the timing components

18. 555 Timer Circuits Three basic circuits… The bistable The monostable
The astable

19. Bistable Block Diagram
Trigger Input
555
Output
Reset Input
The bistable Output is stable in both states, high and low

20. Bistable Timing Diagram
Trigger Input
Output
Reset Input
Bistable Triggered
Bistable Reset

21. Monostable Block Diagram
Trigger Input
555
Output
Timing Components
The monostable Output is stable in the low state only
Triggering makes the Output go high for a set length of time

22. Monostable Timing Diagram
Trigger Input
Output
Monostable Triggered
Time period T

23. The Timing Components Vs 0V
Resistor R
Capacitor C

24. Astable Block Diagram Output
555
Output
Timing Components
The astable Output is not stable at all. It repeatedly goes high for a set time and then low for a set time

25. Astable Timing Diagram
Output
Tmark
Tspace

26. The Timing Components Vs 0V
Resistor R1
Capacitor C
Resistor R2

27. The Timing Components

28. Practical Matters Three ways to build circuits…
Breadboard for prototypes
Stripboard to produce final design
Printed Circuit Board (PCB) to produce final design

29. Breadboard

30. Stripboard

31. Printed Circuit Board (PCB)

32. Lecture Summary What you have learned…
How to treat a system as a ‘black box’ with inputs, a process, and outputs
How to break a problem into small blocks
How to use the 555 timer IC inputs and outputs
What the bistable, monostable and astable circuits do
How to test and construct circuits

34. Resistors Resistance is measured in Ohms (Ω)
Most resistors have four coloured bands
Band 2
2nd Digit
Band 3
Multiplier
Band 4
Tolerance
Band 1
1st Digit

35. The Resistor Colour Code
Band 1 1st Digit   
Band 2 2nd Digit
Band 3 Multiplier
Band 4 Tolerance
     
Black
x 1 -
Brown 1
x 10 1%
Red 2
x 100 2%
Orange 3
x 1,000
Yellow 4
x 10,000
Green 5
x 100,000
Blue 6
x 1,000,000
Violet 7
Grey 8
White 9
Gold 5%
Silver
10%

36. Construction – The Resistors
The 1kΩ resistors
Brown
Black
Red
Gold 5% 1 00

37. Construction – The Resistors
Resistors R1 and R2: 1kΩ (brown, black, red, gold)

38. Construction – The Resistors
Grey
Red
Brown
Gold 5% 8 2

39. Construction – The Resistors
Resistor R3: 820Ω (grey, red, brown, gold)

40. Diodes Diodes only let current flow through them in one direction
1N4001 Rectifier Diode + -
1N4148 Signal Diode + -

41. Construction – The Diodes
Diode D1: 1N4001 (black with grey band)

42. Construction – The Diodes
Diodes D2 and D3: 1N4148 (orange with black band)

43. Light Emitting Diodes (LEDs)
Like diodes, current only flows through them in one direction
Three ways of identifying negative lead:
The shortest lead - +
Largest ‘triangle’ inside the LED
Flat on the LED package

44. Construction – The LED
LED D4: Green 3mm LED

45. Construction – The 555 Timer
IC1: 555 IC Holder

46. Construction – The Jumper Pins
J1 and J2: ‘Smoothing’ and ‘Relay’ jumpers

47. Capacitors Metallised Polyester Capacitors
Electrolytic Capacitors (polarised) - +

48. Construction – Capacitors
Capacitors C1 and C2: 0.01μF (blue)

49. Construction – Capacitors
Capacitor C3: 220μF (smallest black)

50. Construction – Capacitors
Capacitor C4: 1000μF (largest black)

51. Construction – Variable Resistor
Variable Resistor VR1: 100kΩ

52. Construction – Terminal Blocks
Terminal Blocks TB1 and TB2

53. Construction – The Relay
Relay RL1

54. Time to Power Up! 0V
+12V
Button M
Motor