STRIPBOARD

Stripboard circuit (copper tracks side)

Stripboard has parallel strips of copper track on one side. The tracks are 0.1" (2.54mm) apart and there are holes every 0.1" (2.54mm).

Stripboard is used to make up permanent, soldered circuits. It is ideal for small circuits with one or two ICs (chips) but with the large number of holes it is very easy to connect a component in the wrong place. For large, complex circuits it is usually best to use a printed circuit board (PCB) if you can buy or make one.

Stripboard requires no special preparation other than cutting to size. It can be cut with a junior hacksaw, or simply snap it along the lines of holes by putting it over the edge of a bench or table and pushing hard, but take care 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. If the copper looks dull, or you can clearly see finger marks, clean the tracks with fine emery paper, a PCB rubber or a dry kitchen scrub before you start soldering.

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Placing components on stripboard

Components are placed on the non-copper side, then the stripboard is turned over to solder the component leads to the copper tracks.

Stripboard layouts are shown from the component side, so the tracks are out of sight under the board. Layouts are normally shown with the tracks running horizontally across the diagram.

Placing components on stripboard requires care. The large number of holes means it is very easy to make a mistake! For most small circuits the best method is to very carefully place the IC holder(s) in the correct position and solder in place. Then you can position all the other components relative to the IC holder(s).

Minor position errors left and right will not usually be a problem because the component will still be connected to the correct tracks. However, up and down position errors must be avoided because just one hole too high or too low will connect the component to the wrong track and therefore the wrong part of the circuit.

Some people like to label the holes with letters (up/down) and numbers (across) to give each hole a 'grid reference' but this still requires careful counting of holes.

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Cutting stripboard tracks

Track cutter

Most stripboard circuits will need to have some tracks cut to break the connection at that point. This is always necessary under ICs, except for the rare cases where opposite pins must be connected. The tracks are cut with a special track cutter tool or a 3mm drill bit.

Places where the tracks must be broken are usually shown with a cross (X). The cuts are made on the underside (copper side) so extra care is needed to identify the correct hole. It is best to cut the track after soldering because the solder joints will make it easier to identify the correct position.

Place the track cutter on the correct hole and twist it to and fro using moderate force. The aim is to break the copper track, not drill a hole through the board! Inspect the cut closely to ensure there is no fine thread of copper left across the break, because even the tiniest piece will conduct.

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Planning a stripboard layout

Converting a circuit diagram to a stripboard layout is not straightforward because the arrangement of components is quite different. Concentrate on the connections between components, not their positions on the circuit diagram.

Collect all the parts you will be using in the circuit so you can use a piece of stripboard to work out the minimum space they require. For some components (such as IC holders) the space required is fixed, but for others you can increase the space to obtain a better layout. For example most resistors require at least 3 hole-spacings if they are to lie flat on the board, but they can easily span across a greater distance.

If necessary resistors can be mounted vertically between adjacent tracks (0.1" spacing) as shown in the diagram. This arrangement can help to produce a simpler layout but the tracks are more likely to be damaged if the resistor is knocked. If you are designing a stripboard layout for a serious long-term purpose it is best to mount all resistors horizontally.

Plan the layout with a pencil and paper (or on computer if you have suitable software) and check your plan very carefully against the circuit diagram BEFORE you attempt to solder any part of the circuit. The best way to explain the planning process is by example, so there is a step-by-step example to follow below.

Download a Stripboard Planning Sheet

To make planning easier it is best to use paper marked with a 0.1" grid to match the spacing of stripboard holes. You can use graph paper or try our Stripboard Planning Sheet which you can download and print out.

Working 'real size' on a 0.1" grid makes it easy to allow the correct space for components, but you will need to draw very neatly. If you prefer to work at an enlarged scale you can use a piece of stripboard for measuring component sizes in 'number of holes'.

IC pin numbers

IC pins are numbered anti-clockwise around the IC starting near the notch or dot. The diagram shows the numbering for 8-pin and 14-pin ICs, but the principle is the same for all sizes.

Components without suitable leads

Some components such as switches and variable resistors do not have suitable leads of their own so you must solder some on yourself. Use stranded plastic-coated wire, single-core wire is not suitable unless the circuit is going to be permanently mounted in a box with no flexing of the wires.

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Planning an example stripboard layout

When planning a stripboard layout you must concentrate on the connections between components, not their positions on the circuit diagram. The best way to explain the planning process is by example, so the section below explains the process step-by-step for a 555 astable circuit which flashes an LED.

The stripboard tracks are horizontal in all the diagrams.

Astable Circuit Diagram

The circuit diagram

The circuit diagram is the starting point for any stripboard layout, even if you have already built a trial circuit on breadboard.

The LED flashes at a rate determined by the resistors R1 and R2 and the capacitor C1. R1 must be at least 1k and both R1 and R2 should not be more than 1M. To select a value for the LED resistor R3 please see the LEDs page.

LED on time: Tm = 0.7 × (R1 + R2) × C1
LED off time: Ts = 0.7 × R2 × C1
T = Tm + Ts = 0.7 × (R1 + 2R2) × C1
Frequency (flashes per second), f = ¹/_T
Tm and Ts are about equal if R2 is much larger than R1.

Planning the layout

1. Place the IC holder near the centre of your planning sheet with pin 1 at the top left (as in the diagram). You may find it helpful to number the pins.

2. Mark breaks in each track under the IC holder with a cross (X). The breaks prevent opposite pins of the IC being connected together. The track beside each pin of the IC is connected to that pin, the diagram shows this for pins 3 and 6.

3. Mark the power supply tracks +Vs and 0V, choose tracks which are 2 or 3 spaces above and below the IC holder as shown in the diagram.

4. Now add the wire links. Draw a 'blob' () at each end of a link. The links are vertical because the stripboard tracks make the horizontal connections. Tinned copper wire (with no insulation) can be used for these links unless there is a risk of them touching other wires (in which case use single core insulated wire). Work round the IC pin-by-pin from pin 1.
   • Draw all the direct links to the supply tracks (+Vs and 0V). The diagram shows pin 1 connected to 0V and pins 4 and 8 connected to +Vs.

   • Draw any links required between pins on the same side of the IC. There are none in the example, but these links are straightforward to add.

   • Links to pins on the other side of the IC require more thought. If the pins happen to be opposite one another you can erase the track break (X) between them. Otherwise the pins can be linked by connecting both of them to an unused track above or below the IC. The diagram shows pins 2 and 6 linked in this way. Another method is to link them with insulated wire bent around the IC.
   
   

   

5. Add components which will be mounted on the stripboard such as resistors, capacitors and diodes. Make sure you allow for their size which determines the minimum number of holes, and sometimes the maximum as well. This is usually the most difficult stage of planning a layout so expect to change your plan several times! Remember to label the components, otherwise it will become confusing once there are several on the plan.

   Connections which do not involve the IC are made using an unused track. For example resistor R3 and the LED are connected by an unused track above the IC.

   Watch for alternative arrangements using the links you have already made. For example the LED needs to connect to 0V but it is a long stretch to the 0V track. It is easier to connect the LED to the same track as pin 1 of the IC because that track is already connected to 0V by a wire link.

   Resistor R2 needs to connect from pin 7 to pin 6 and it could do this directly by mounting it vertically. However, it has been connected from pin 7 to the track used to link pins 2 and 6, the extra space this gives allows R2 to lie horizontally on the board.

   
   

6. Add wires to components which will be off the stripboard such as switches. These should normally be on the left and right at the edges of the board. Start by adding the battery clip or power supply leads to the +Vs and 0V tracks. Connections for the other off-board components are usually easy because you do not need to allow for their size, just draw wires to the correct tracks.

7. Check your plan very carefully by checking every connection shown on the circuit diagram. A good way to do this is to work round the IC pin-by-pin. Check all the connections and components connected to pin 1, then move on to pin 2, and so on.

   
   

8. Look for ways to improve your plan. For example it may be possible to eliminate an unused track by moving a supply track nearer to the IC - but make sure there is still sufficient space for the components. It may also be possible to move links and components closer to the IC horizontally to make the area of board required a little smaller.

   Unused tracks above and below the IC have been eliminated in the example. This affected two components, resistor R1 and capacitor C1, but both will still fit in the reduced space. The plan could be compressed a little further by moving components and links closer to the IC horizontally but this has not been done.

   
   

9. Finally, check your plan again and make a neat copy fully labelled with all the component references or values. Work out the size of stripboard required. Notice that an extra hole has been allowed on the left and right to avoid soldering at the end of a track. Joints made at the end of a track are likely to break because the small piece of track beyond the last hole easily breaks away from the board.

   It is tempting to rush straight into soldering the circuit, but do check your plan carefully first. It is much easier to correct errors on the plan than it is to correct to correct them on the soldered board!

This example plan is just one of the many possible layouts for the circuit. The Flashing LED uses the same circuit, but the stripboard plan is quite different. In this case the aim was to have the minimum number of wire links.

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The completed stripboard layout and the circuit diagram for comparison:

Flashing LED Circuit

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Logic Gates

Introduction to logic gates:

Logic gates process signals which represent true or false. Normally the positive supply voltage +Vs represents true and 0V represents false. Other terms which are used for the true and false states are shown in the table on the right. It is best to be familiar with them all.

The different types of gates are as follows:-

• NOT GATE

  Logic states
  True	False
  1	0
  High	Low
  +Vs	0V
  On	Off

• AND GATE
  
• NAND GATE
  
• OR GATE
• NOR GATE
• EX-OR GATE
• EX-NOR GATE

Logic gate symbols...

There are two series of symbols for logic gates: The traditional symbols have distinctive shapes making them easy to recognise so they are widely used in industry and education.



International Electrotechnical Commission symbols are rectangles with a symbol inside to show the gate function. They are rarely used despite their official status, but you may need to know them for an examination.

Inputs and outputs

Gates have two or more inputs, except a NOT gate which has only one input. All gates have only one output. Usually the letters A, B, C and so on are used to label inputs, and Q is used to label the output. On this page the inputs are shown on the left and the output on the right.

The inverting circle (o)

Some gate symbols have a circle on their output which means that their function includes inverting of the output. It is equivalent to feeding the output through a NOT gate. For example the NAND (Not AND) gate symbol shown on the right is the same as an AND gate symbol but with the addition of an inverting circle on the output.

Truth tables

Input A	Input B	Output Q
0	0	0
0	1	0
1	0	0
1	1	1

A truth table is a good way to show the function of a logic gate. It shows the output states for every possible combination of input states. The symbols 0 (false) and 1 (true) are usually used in truth tables. The example truth table on the right shows the inputs and output of an AND gate.

Logic ICs

Logic gates are available on special ICs (chips) which usually contain several gates of the same type, for example the 4001 IC contains four 2-input NOR gates. There are several families of logic ICs and they can be split into two groups:

NOT gate (inverter)

The output Q is true when the input A is NOT true, the output is the inverse of the input: Q = NOT A
A NOT gate can only have one input. A NOT gate is also called an inverter.

		Input A Output Q 0 1 1 0
Traditional symbol	IEC symbol	Truth Table

AND gate

The output Q is true if input A AND input B are both true: Q = A AND B
An AND gate can have two or more inputs, its output is true if all inputs are true.

		Input A Input B Output Q 0 0 0 0 1 0 1 0 0 1 1 1
Traditional symbol	IEC symbol	Truth Table

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NAND gate (NAND = Not AND)

This is an AND gate with the output inverted, as shown by the 'o' on the output.
The output is true if input A AND input B are NOT both true: Q = NOT (A AND B)
A NAND gate can have two or more inputs, its output is true if NOT all inputs are true.

		Input A Input B Output Q 0 0 1 0 1 1 1 0 1 1 1 0
Traditional symbol	IEC symbol	Truth Table

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OR gate

The output Q is true if input A OR input B is true (or both of them are true): Q = A OR B
An OR gate can have two or more inputs, its output is true if at least one input is true.

		Input A Input B Output Q 0 0 0 0 1 1 1 0 1 1 1 1
Traditional symbol	IEC symbol	Truth Table

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NOR gate (NOR = Not OR)

This is an OR gate with the output inverted, as shown by the 'o' on the output.
The output Q is true if NOT inputs A OR B are true: Q = NOT (A OR B)
A NOR gate can have two or more inputs, its output is true if no inputs are true.

		Input A Input B Output Q 0 0 1 0 1 0 1 0 0 1 1 0
Traditional symbol	IEC symbol	Truth Table

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EX-OR (EXclusive-OR) gate

The output Q is true if either input A is true OR input B is true, but not when both of them are true: Q = (A AND NOT B) OR (B AND NOT A)
This is like an OR gate but excluding both inputs being true.
The output is true if inputs A and B are DIFFERENT.
EX-OR gates can only have 2 inputs.

		Input A Input B Output Q 0 0 0 0 1 1 1 0 1 1 1 0
Traditional symbol	IEC symbol	Truth Table

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EX-NOR (EXclusive-NOR) gate

This is an EX-OR gate with the output inverted, as shown by the 'o' on the output.
The output Q is true if inputs A and B are the SAME (both true or both false): Q = (A AND B) OR (NOT A AND NOT B)
EX-NOR gates can only have 2 inputs

		Input A Input B Output Q 0 0 1 0 1 0 1 0 0 1 1 1
Traditional symbol	IEC symbol	Truth Table

Combinations of logic gates Logic gates can be combined to produce more complex functions. They can also be combined to one type of gate for another. Input A Input B Output Q 0 0 0 0 1 0 1 0 1 1 1 0 For example to produce an output Q which is true only when input A is true and input B is false, as shown in the truth table on the right, we can combine a NOT gate and an AND gate like this: Q = A AND NOT B Working out the function of a combination of gates Truth tables can be used to work out the function of a combination of gates. Inputs Outputs A B C D E Q 0 0 0 1 0 1 0 0 1 1 0 1 0 1 0 0 0 0 0 1 1 0 1 1 1 0 0 0 0 0 1 0 1 0 0 0 1 1 0 0 0 0 1 1 1 0 1 1 For example the truth table on the right show the intermediate outputs D and E as well as the final output Q for the system shown below. D = NOT (A OR B) E = B AND C Q = D OR E = (NOT (A OR B)) OR (B AND C) Substituting one type of gate for another Logic gates are available on ICs which usually contain several gates of the same type, for example four 2-input NAND gates or three 3-input NAND gates. This can be wasteful if only a few gates are required unless they are all the same type. To avoid using too many ICs you can reduce the number of gate inputs or substitute one type of gate for another. Reducing the number of inputs The number of inputs to a gate can be reduced by connecting two (or more) inputs together. The diagram shows a 3-input AND gate operating as a 2-input AND gate. Making a NOT gate from a NAND or NOR gate Reducing a NAND or NOR gate to just one input creates a NOT gate. The diagram shows this for a 2-input NAND gate. Any gate can be built from NAND or NOR gates As well as making a NOT gate, NAND or NOR gates can be combined to create any type of gate! This enables a circuit to be built from just one type of gate, either NAND or NOR. For example an AND gate is a NAND gate then a NOT gate (to undo the inverting function). Note that AND and OR gates cannot be used to create other gates because they lack the inverting (NOT) function. To change the type of gate, such as changing OR to AND, you must do three things: Invert (NOT) each input. Change the gate type (OR to AND, or AND to OR) Invert (NOT) the output. For example an OR gate can be built from NOTed inputs fed into a NAND (AND + NOT) gate. NAND gate equivalents The table below shows the NAND gate equivalents of NOT, AND, OR and NOR gates: Gate Equivalent in NAND gates NOT AND OR NOR Substituting gates in an example logic system The original system has 3 different gates: NOR, AND and OR. This requires three ICs (one for each type of gate). To re-design this system using NAND gates only begin by replacing each gate with its NAND gate equivalent, as shown in the diagram below. Then simplify the system by deleting adjacent pairs of NOT gates (marked X above). This can be done because the second NOT gate cancels the action of the first. The final system is shown on the right. It has five NAND gates and requires two ICs (with four gates on each IC). This is better than the original system which required three ICs (one for each type of gte). Substituting NAND (or NOR) gates does not always increase the number of gates, but when it does (as in this example) the increase is usually only one or two gates. The real benefit is reducing the number of ICs required by using just one type of gate.

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