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Integrated Circuits (Chips)

Also see: 4000
Series ICs |
74 Series ICs | 555 and
556 Timer Circuits

Integrated Circuits are usually called ICs or chips. They are complex
circuits which have been etched onto tiny chips of semiconductor (silicon). The
chip is packaged in a plastic holder with pins spaced on a 0.1" (2.54mm) grid
which will fit the holes on stripboard and breadboards. Very fine wires inside
the package link the chip to the pins.

Pin numbers

The pins are numbered anti-clockwise around the IC (chip)
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.

IC holders (DIL sockets)

ICs (chips) are easily damaged by heat when soldering and their short pins
cannot be protected with a heat sink. Instead we use an IC holder, strictly
called a DIL socket (DIL = Dual In-Line), which can be safely soldered onto the
circuit board. The IC is pushed into the holder when all soldering is complete.

IC holders are only needed when soldering so they are not used on
breadboards.

Commercially produced circuit boards often have ICs soldered directly
to the board without an IC holder, usually this is done by a machine which is
able to work very quickly. Please don't attempt to do this yourself because you
are likely to destroy the IC and it will be difficult to remove without damage
by de-soldering.

Removing an IC from its holder

If you need to remove an IC it can be gently prised out of
the holder with a small flat-blade screwdriver. Carefully lever up each end by
inserting the screwdriver blade between the IC and its holder and gently
twisting the screwdriver. Take care to start lifting at both ends before you
attempt to remove the IC, otherwise you will bend and possibly break the pins.

Static precautions

Many ICs are static sensitive and can be damaged when
you touch them because your body may have become charged with static
electricity, from your clothes for example. Static sensitive ICs will be
supplied in antistatic packaging with a warning label and they should be left in
this packaging until you are ready to use them.

It is usually adequate to earth your hands by touching a
metal water pipe or window frame before handling the IC but for the more
sensitive (and expensive!) ICs special equipment is available, including earthed
wrist straps and earthed work surfaces. You can make an earthed work surface
with a sheet of aluminium kitchen foil and using a crocodile clip to connect the
foil to a metal water pipe or window frame with a 10k

Antistatic bags for ICs
resistor in series.

Photograph © Rapid
Electronics

PDF files

To view and print PDF files you need an Acrobat Reader which may
be downloaded free for

Windows,

Mac, RISC OS,
or

UNIX/Linux computers. If you are not sure which type of computer you
have it is probably Windows.

Datasheets

Datasheets are available for most ICs giving detailed
information about their ratings and functions. In some cases example circuits
are shown. The large amount of information with symbols and abbreviations can
make datasheets seem overwhelming to a beginner, but they are worth reading as
you become more confident because they contain a great deal of useful
information for more experienced users designing and testing circuits.

Datasheets are available as PDF files from:

DatasheetArchive.com

Datasheets.org.uk

DatasheetCatalog.com

Sinking and sourcing current

IC outputs are often said to 'sink' or 'source' current. The terms refer to the

direction of the current at the IC's output.

If the IC is sinking current it is flowing into the output.
This means that a device connected between the positive supply (+Vs) and the IC
output will be switched on when the output is low (0V).

If the IC is sourcing current it is flowing out of the output.
This means that a device connected between the IC output and the negative supply
(0V) will be switched on when the output is high (+Vs).

It is possible to connect two devices to an IC output so that one is on when
the output is low and the other is on when the output is high. This arrangement
is used in the
Level Crossing project to make the red LEDs flash alternately.

The maximum sinking and sourcing currents for an IC output are usually the
same but there are some exceptions, for example
74LS TTL logic
ICs can sink up to 16mA but only source 2mA.

Using diodes to combine outputs

The outputs of ICs must never be directly connected together. However, diodes
can be used to combine two or more digital (high/low) outputs from an IC such as
a counter. This can be a useful way of producing simple logic functions without
using logic gates!

The diagram shows two ways of combining outputs using diodes.
The diodes must be capable of passing the output current. 1N4148 signal diodes
are suitable for low current devices such as LEDs.

For example the outputs Q0 - Q9 of a
4017 1-of-10
counter go high in turn. Using diodes to combine the 2nd (Q1) and 4th (Q3)
outputs as shown in the bottom diagram will make the LED flash twice followed by
a longer gap. The diodes are performing the function of an
OR gate.

Example projects:
Traffic Light
| Dice |
Model Lighthouse

The 555 and 556 Timers

The 8-pin 555 timer IC is used in many projects, a popular
version is the NE555. Most circuits will just specify '555 timer IC' and the
NE555 is suitable for these. The 555 output (pin 3) can
sink and
source up to 200mA. This is more than most ICs and it is sufficient to
supply LEDs, relay coils and low current lamps. To switch larger currents you
can connect a transistor.

The 556 is a dual version of the 555 housed in a 14-pin
package. The two timers (A and B) share the same power supply pins.

Low power versions of the 555 are made, such as the ICM7555,
but these should only be used when specified (to increase battery life) because
their maximum output current of about 20mA (with 9V supply) is too low for many
standard 555 circuits. The ICM7555 has the same pin arrangement as a standard
555.

For further information please see the page on
555 and 556 timer circuits.

Logic ICs (chips)

Logic ICs process
digital signals and there are many devices, including

logic gates, flip-flops,

shift registers, counters and display drivers. They can be split into two groups

according to their pin arrangements: the

4000 series and

the 74 series

which consists of various families such as the 74HC, 74HCT and 74LS.

For most new projects the 74HC family is the best
choice. The older 4000 series is the only family which works with a
supply voltage of more than 6V. The 74LS and 74HCT families require a 5V supply
so they are not convenient for battery operation.

The table below summarises the important properties of the most popular logic
families:

Property	4000 Series	74 Series 74HC	74 Series 74HCT	74 Series 74LS
Technology	CMOS	High-speed CMOS	High-speed CMOS TTL compatible	TTL Low-power Schottky
Power Supply	3 to 15V	2 to 6V	5V ±0.5V	5V ±0.25V
Inputs	Very high impedance. Unused inputs must be connected to +Vs or 0V. Inputs cannot be reliably driven by 74LS outputs unless a 'pull-up' resistor is used (see below).		Very high impedance. Unused inputs must be connected to +Vs or 0V. Compatible with 74LS (TTL) outputs.	'Float' high to logic 1 if unconnected. 1mA must be drawn out to hold them at logic 0.
Outputs	Can sink and source about 5mA (10mA with 9V supply), enough to light an LED. To switch larger currents use a transistor.	Can sink and source about 20mA, enough to light an LED. To switch larger currents use a transistor.	Can sink and source about 20mA, enough to light an LED. To switch larger currents use a transistor.	Can sink up to 16mA (enough to light an LED), but source only about 2mA. To switch larger currents use a transistor.
Fan-out	One output can drive up to 50 CMOS, 74HC or 74HCT inputs, but only one 74LS input.	One output can drive up to 50 CMOS, 74HC or 74HCT inputs, but only 10 74LS inputs.		One output can drive up to 10 74LS inputs or 50 74HCT inputs.
Maximum Frequency	about 1MHz	about 25MHz	about 25MHz	about 35MHz
Power consumption of the IC itself	A few µW.	A few µW.	A few µW.	A few mW.

Mixing
Logic Families

It is best to build a circuit using just one logic family,
but if necessary the different families may be mixed providing the power supply
is suitable for all of them. For example mixing 4000 and 74HC requires the power
supply to be in the range 3 to 6V. A circuit which includes 74LS or 74HCT ICs
must have a 5V supply.

A 74LS output cannot reliably drive a 4000 or 74HC input
unless a 'pull-up' resistor of 2.2k

is connected between the +5V supply and the input to correct the slightly
different logic voltage ranges used.

Note that a 4000 series output can drive only one 74LS input.

Driving 4000 or 74HC inputs from a

74LS output using a pull-up resistor.

4000 Series CMOS

This family of logic ICs is numbered from 4000 onwards, and from 4500
onwards. They have a B at the end of the number (e.g. 4001B) which refers to an
improved design introduced some years ago. Most of them are in 14-pin or 16-pin
packages. They use CMOS circuitry which means they use very little power
and can tolerate a wide range of power supply voltages (3 to 15V) making them
ideal for battery powered projects. CMOS is pronounced 'see-moss' and stands
for Complementary Metal Oxide Semiconductor.

However the CMOS circuitry also means that they are
static sensitive.
Touching a pin while charged with static electricity (from your clothes for
example) may damage the IC. In fact most ICs in regular use are quite tolerant
and earthing your hands by touching a metal water pipe or window frame before
handling them will be adequate. ICs should be left in their protective packaging
until you are ready to use them. For the more sensitive (and expensive!) ICs
special equipment is available, including earthed wrist straps and earthed work
surfaces.

For further information, including pin connections, please use the quick
links on the right or go to
4000 Series ICs.

Quick links to

individual ICs

4000 4060 4001 4068 4002 4069 4011 4070 4012 4071 4017 4072 4020 4073 4023 4075 4024 4077 4025 4081 4026 4082 4028 4093 4029 4510 4030 4511 4040 4516 4049 4518 4050 4520

4 Series: 74LS, 74HC and 74HCT

There are several families of logic ICs numbered from 74xx00 onwards with

letters (xx) in the middle of the number to indicate the type of circuitry, eg

74LS00 and 74HC00. The original family (now obsolete) had no letters, eg 7400.

The 74LS (Low-power Schottky) family (like the original) uses TTL
(Transistor-Transistor Logic) circuitry which is fast but requires more power
than later families.

The 74HC family has High-speed CMOS circuitry, combining the speed of
TTL with the very low power consumption of the 4000 series. They are CMOS ICs
with the same pin arrangements as the older 74LS family. Note that 74HC inputs
cannot be reliably driven by 74LS outputs because the voltage ranges used for
logic 0 are not quite compatible, use 74HCT instead.

The 74HCT family is a special version of 74HC with 74LS TTL-compatible
inputs so 74HCT can be safely mixed with 74LS in the same system. In fact 74HCT
can be used as low-power direct replacements for the older 74LS ICs in most
circuits. The minor disadvantage of 74HCT is a lower immunity to noise, but this
is unlikely to be a problem in most situations.

Beware that the 74 series is often still called the 'TTL series' even
though the latest ICs do not use TTL!

For further information, including pin connections, please use the quick
links on the right or go to
74 series ICs.

Quick links to

individual ICs

7400 7432 7402 7442 7403 7447 7404 7486 7405 7490 7408 7493 7409 74132 7410 74160 7411 74161 7412 74162 7414 74163 7420 74192 7421 74193 7427 74390 7430 74393 74HC4017 74HC4020 74HC4040 74HC4060 74HC4511

The CMOS circuitry used in the 74HC and 74HCT series ICs means
that they are
static sensitive. Touching a pin while charged with static electricity (from
your clothes for example) may damage the IC. In fact most ICs in regular use are
quite tolerant and earthing your hands by touching a metal water pipe or window
frame before handling them will be adequate. ICs should be left in their
protective packaging until you are ready to use them.

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