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Block Diagrams

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Block Diagrams



Block diagrams are used to understand (and design) complete circuits by breaking them down into smaller sections or blocks. Each block performs a particular function and the block diagram shows how they are connected together. No attempt is made to show the components used within a block, only the inputs and outputs are shown. This way of looking at circuits is called thesystems approach.
Power supply (or battery) connections are usually not shown on block diagrams.


Audio Amplifier System

Block Diagram of an Audio Amplifier System 
The power supply (not shown) is connected to the pre-amplifier and power amplifier blocks.
  • Microphone - a transducer which converts sound to voltage.
  • Pre-Amplifier - amplifies the small audio signal (voltage) from the microphone.
  • Tone and Volume Controls - adjust the nature of the audio signal. 
    The tone control adjusts the balance of high and low frequencies.
    The volume control adjusts the strength of the signal.
  • Power Amplifier - increases the strength (power) of the audio signal.
  • Loudspeaker - a transducer which converts the audio signal to sound.


Radio Receiver System

Block Diagram of a Radio Receiver System 
The power supply (not shown) is connected to the audio amplifier block.
  • Aerial - picks up radio signals from many stations.
  • Tuner - selects the signal from just one radio station.
  • Detector - extracts the audio signal carried by the radio signal.
  • Audio Amplifier - increases the strength (power) of the audio signal. 
    This could be broken down into the blocks like the Audio Amplifier System shown above.
  • Loudspeaker - a transducer which converts the audio signal to sound.


Regulated Power Supply System

Block Diagram of a Regulated Power Supply System 
  • Transformer - steps down 230V AC mains to low voltage AC.
  • Rectifier - converts AC to DC, but the DC output is varying.
  • Smoothing - smooths the DC from varying greatly to a small ripple.
  • Regulator - eliminates ripple by setting DC output to a fixed voltage.
For futher information please see the Power Supplies page.


Feedback Control System

Block Diagram of a Feedback Control System 
The power supply (not shown) is connected to the control circuit block.
  • Sensor - a transducer which converts the state of the controlled quantity to an electrical signal.
  • Selector (control input) - selects the desired state of the output. Usually it is a variable resistor.
  • Control Circuit - compares the desired state (control input) with the actual state (sensor) of the controlled quantity and sends an appropriate signal to the output transducer.
  • Output Transducer - converts the electrical signal to the controlled quantity.
  • Controlled Quantity - usually not an electrical quantity, e.g. motor speed.
  • Feedback Path - usually not electrical, the Sensor detects the state of the controlled quantity.

Starter kit of components

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Starter kit of components

Also see: Tools for electronics | Making a workbench 
componentsIf you are new to electronics and would like to try adapting published projects, or designing and building your own circuits, you need to have a small stock of components available. However, there is a very wide range of components and it can be difficult to know which ones you really need! I hope the list below will help you choose a sensible selection which is within your budget. Remember that circuits built on breadboard can be dismantled after use and the components re-used.
It is usually cheapest to buy components by mail order and several suppliers are listed on the Links page. Send for a catalogue first, even if you have to pay for it, because most include a great deal of useful information as well as listing part numbers and prices. Kits of assorted components may be available and this is a great way to start if you can afford the initial cost. Remember that you will need to organise storage of the components! 




Essential components

These are the components used in most projects. The individual components are quite cheap, but the total cost of the set will be significant! One way to spread the cost is to add a few items from this list every time you buy the components for a particular project. Click on the titles for further information.

Resistors

resistor0.25W carbon film resistors are the cheapest type. Choose ones with 4-band colour codes because these are easier to read (the precision of 5-band codes is unnecessary).
Ideally you need a good selection of values over the range 100ohm to 1Mohm such as the E6 or E12 series, but that is a large number of resistors! As a minimum I suggest: 470*, 1k*, 2k2, 4k7, 10k*, 22k, 33k, 47k, 100k, 220k, 470k and 1Mohm. Buy at least 10 of each value and 20 of those marked *. The 470ohm resistors are for use with LEDs, even if a project specifies a slightly different value.
Resistors may be combined in series and parallel to obtain extra values, for example 100kohm and 220kohm in series is 320kohm which is close enough to 330kohm

small value capacitors
electrolytic capacitor

Capacitors

Low values: 0.01µF and 0.1µF metallised polyester, 10 of each.
High values: 1µF 63V, 10µF 25V, and 100µF 25V electrolytic with radial leads, 10 of each; 220µF 25V and 470µF 25V electrolytic with axial leads, 3 of each. 

Diodes

diodes1N4148 signal diode and 1N4001 rectifier diode, 5 of each. 

LEDs

LEDRed, yellow and green 5mm standard LEDs, 10 of each. 

transistors

Transistors

About 5 general purpose, low power, NPN transistors. These should have a maximum collector current (Ic max) of 100mA, and a minimum current gain (hFE min) of 200. 
For example: BC548B (BC108 equivalent).
About 5 general purpose, medium power, NPN transistors. These should have a maximum collector current (Ic max) of 1A, and a minimum current gain (hFE min) of 30.
For example: BC639 (BFY51 equivalent). 

Integrated circuits ('chips') and holders

555 timer IC
IC holder
NE555 timer IC, at least 3 (10 if you plan to solder projects). It is not worth ordering other ICs at this stage unless you know they are needed for some of the projects you wish to try.
If you are planning to solder circuits on stripboard or PCB you will also need 8-pin, 14-pin and 16-pin DIL sockets (IC holders), at least 10 of each. 

Variable resistors

variable resistor
Standard Variable Resistor

Presets are cheaper than standard variable resistors but most have pins which are too large for breadboards. For breadboard circuits is is probably best to buy standard variable resistors and solder short single core 1/0.6mm wires onto them.
The useful values are: 10k LIN, 100k LIN and 1Mohm LIN, buy 2 of each. A 1Mohm LOG potentiometer is useful too. Knobs are optional because it is easy to turn the spindles by hand. If you buy presets the horizontal style are best, all presets are LIN. 

battery clip

Battery clips

Clip for a 9V PP3 battery, buy 3 (or 10 if you plan to solder projects). Remember to buy a battery too! 

Wire

single core wire
stranded wire
Red and black 7/0.2mm stranded wire, one colour of single-core 1/0.6mm wire, 10m (or a reel) of each. If you are planning to build projects on breadboard buy extra colours of the single-core wire, including red and black. 

Crocodile clips

crocodile clipinsulated crocodile clip

Buy at least one standard crocodile clip to use as a heat sink when soldering. Miniature red and black crocodile clips (buy about 10 of each) are useful for making your own test leads using 7/0.2mm stranded wire. 

push-to-make switchSPDT toggle switch

Switches

Switches are not essential for breadboard circuits because you can make or break links with pieces of wire. The on/off switch from soldered projects can also be omitted if you are willing to unclip the battery instead.
If you wish to buy a few switches the most useful types are push-to-make and miniature SPDT toggle switches, 3 of each. 

stripboard

Stripboard

Buy a large sheet (or two) and cut it up as required. You can cut it neatly to size using a junior hacksaw, cutting along the lines of holes is easiest. For quickness you can break it over the edge of a workbench along the lines of holes - take care though because this needs a fairly large force and the edges will be rough. You may need to use a large pair of pliers to nibble away any jagged parts.
Avoid handling stripboard that you are not planning to use immediately because sweat from your hands will corrode the copper tracks and this will make soldering difficult unless you clean the board first. 

breadboard

Breadboard

A small breadboard (such as the Protobloc 1 shown in the picture) is suitable for simple circuits with up to two ICs, but if you intend to build more complex circuits such as counters it is best to buy a larger breadboard (such as the Protobloc 2).
Breadboards do not require soldering so the components used on them can be re-used many times. They are ideal for testing your own circuit designs and trying out ideas such as adapting a published project. 

Other components to consider

piezo transducer
Miniature piezo transducer

Buy these if you can afford them, or wait until they are needed for a project.
  • A light dependent resistor (LDR), ORP12 or NORPS12.
  • A thermistor, miniature disc type, NTC about 5kohm@25°C.
  • A piezo transducer with flying leads.
  • A buzzer or bleeper.
  • A miniature loudspeaker 8ohm.



Storage systems for components

snap-top plastic bags
Snap-top plastic bags
drawers cabinet
Drawer cabinet
You can store all your components in a single container, such as a plastic food box, but as you accumulate more items it will become increasingly difficult to find the smaller components! A cheap solution is to organise the parts into small snap-top plastic bags which can be labelled, in fact you may find that some components are supplied like this.
Probably the best storage system is a cabinet of plastic drawers. These can be expensive, but you do not need many drawers because there is no need to have a drawer for every single component value. Many parts can be grouped together, such as decades of resistor values. For example you could organise a 15-drawer cabinet like this:
  1. Resistors 10ohm+ (third band blackonly a few, but they tend to be large
  2. Resistors 100ohm+ (third band brown)
  3. Resistors 1kohm+ (third band red)
  4. Resistors 10kohm+ (third band orange)
  5. Resistors 100kohm+ (third band yellow)
  6. Resistors 1Mohm+ (third band green) and 10Mohm (third band blue)
  7. Presets, also variable resistors if they will fit in the drawer
  8. Capacitors low values, less than 1µF
  9. Capacitors electrolytic 1µF+
  10. Diodes and transistors
  11. LEDs and lamps (also LED clips and lampholders)
  12. ICs (chips) and their holders (DIL sockets)
  13. Switches and relays
  14. Connectors (crocodile clips, plugs and sockets)
  15. Other components (battery clips, piezo transducers, LDRs, thermistors)

Tools required for electronics

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Tools required for electronics

Also see: Starter kit | Workbench | Soldering guide





Soldering iron, photograph © Rapid Electronics

Soldering iron

For electronics work the best type is one powered by mains electricity (230V in the UK), it should have a heatproof cable for safety. The iron's power rating should be 15 to 25W and it should be fitted with a small bit of 2 to 3mm diameter.

Other types of soldering iron 
Low voltage soldering irons are available, but their extra safety is undermined if you have a mains lead to their power supply! Temperature controlled irons are excellent for frequent use, but not worth the extra expense if you are a beginner. Gas-powered irons are designed for use where no mains supply is available and are not suitable for everyday use. Pistol shaped solder guns are far too powerful and cumbersome for normal electronics use.

Soldering iron stand, photograph © Rapid Electronics

Soldering iron stand

You must have a safe place to put the iron when you are not holding it. The stand should include a sponge which can be dampened for cleaning the tip of the iron.


Solder sucker, photograph © Rapid Electronics

Desoldering pump (solder sucker)

A tool for removing solder when desoldering a joint to correct a mistake or replace a component.


Solder remover wick (copper braid)

This is an alternative to the desoldering pump shown above.


Solder reels, photograph © Rapid Electronics

Reel of solder

The best size for electronics is 22swg (swg = standard wire gauge).


Side cutters, photograph © Rapid Electronics

Side cutters

For trimming component leads close to the circuit board.


Wire strippers (automatic), photograph © Rapid Electronics

Wire strippers

Most designs include a cutter as well, but they are not suitable for trimming component leads.
Photograph © Rapid Electronics 

Snipe nose pliers, photograph © Rapid Electronics

Small pliers

Usually called 'snipe nose' pliers, these are for bending component leads etc. If you put a strong rubber band across the handles the pliers make a convenient holder for parts such as switches while you solder the contacts.


Screwdriver, photograph © Rapid Electronics

Small flat-blade screwdriver

For scraping away excess flux and dirt between tracks, as well as driving screws!


Crocodile clip, photograph © Rapid Electronics

Heat sink

You can buy a special tool, but a standard crocodile clip works just as well and is cheaper.


Track cutter, photograph © Rapid ElectronicsThe following tool is only required if you are using stripboard:

Track cutter

A 3mm drill bit can be used instead, in fact the tool is usually just a 3mm drill bit with a proper handle fitted.


PCB rubber, photograph © Rapid ElectronicsThe following tools are only required if you make your own PCBs:

PCB rubber

This is an abrasive rubber for cleaning PCBs. It can also be used to clean stripboard where the copper tracks have become dull and tarnished.

PCB drill in stand, photograph © Rapid Electronics

Small electric drill

Ideally this should be mounted in a drill stand. You will need a range of small drill bits, but for most holes a 1mm bit is suitable. Larger holes can be drilled with a hand drill but 1mm bits are too fragile to use reliably in a hand drill.