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

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

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

The Block Diagram Input Process 1 Process 2 Process 3 Output

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

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

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

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

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

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

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

Lamps Connecting a lamp to the 555 Output by ‘sourcing’ current Output 0V Lamp Output

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

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

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

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

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

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

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

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

Monostable Timing Diagram Trigger Input Output Monostable Triggered Time period T

The Timing Components Vs 0V Resistor R Capacitor C

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

Astable Timing Diagram Output Tmark Tspace

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

The Timing Components

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

Breadboard

Stripboard

Printed Circuit Board (PCB)

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

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

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%

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

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

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

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

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

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

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

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

Construction – The LED LED D4: Green 3mm LED

Construction – The 555 Timer IC1: 555 IC Holder

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

Capacitors Metallised Polyester Capacitors Electrolytic Capacitors (polarised) - +

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

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

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

Construction – Variable Resistor Variable Resistor VR1: 100kΩ

Construction – Terminal Blocks Terminal Blocks TB1 and TB2

Construction – The Relay Relay RL1

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