Components for Building Combinational Circuits
CSCI226
Breadboards.
In order to temporarily construct a circuit without damaging the components used to build it, we must
have some sort of a platform that will both hold the components in place and provide the needed
electrical connections. Although more sophisticated techniques and devices have been developed to
make the assembly and testing of electronic circuits easier, the concept of the breadboard, from the
early amateur radio operator, remains, and the process of assembling components on a temporary
platform is still known as breadboarding.
The breadboards we provide are molded nylon, 6½" long and 2¼" wide. There is a molded groove along
the center. There are two long rows at the top (labeled red and blue) and two rows at the bottom
(again labeled red and blue). All of the holes along one row are electrically connected to each other but
insulated from the holes in every other row or column. Above the center groove are columns. Each
column has five holes that are electrically connected together but insulated from all the other columns
and from the red and blue rows. Below the center groove are more columns, arranged in a similar way.
(The right side of the picture is a “cut-away” showing the hidden electrical connections.)
–
+
–
+
Most circuit components need to connect to power, ground, and one or two other components. The red
and blue rows are intended to distribute power (red row, +) to all of the circuit components and to serve
as a ground (blue row, -). The columns in the middle are for everything else.
These breadboards are sturdy and can take quite a bit of handling. However, to avoid damage to the
internal electrical contacts and the electrical components, there are a few rules to observe:
 Always make sure power is disconnected when constructing or modifying your experimental circuit.
It is possible to damage components or incur an electrical shock if you leave power connected when
making changes.
 Never put anything larger than AWG #22 into the holes. AWG #24 wire (a bit thinner, used for
landline telephone wiring) is an excellent choice. We give you a mix of AWG #22 and #24 wire.
 Be gentle: Never force component leads into contact holes on the breadboard socket. Doing so can
damage the contact and make it useless.
 Don’t push jumper wires or component leads too deep into the holes. Only a thin foam layer
protects the metal baseplate. You can cause a short circuit if you punch through to the baseplate.
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Integrated Circuits.
We have an assortment of types and a switch device. Digital ICs may be of the 7400 TTL (TransistorTransistor Logic) series, the 4000 CMOS (Complementary Metal Oxide Semiconductor) series, or the
74HCT00 series, which are CMOS devices with 7400-series pin configuration. For example, your kit
should have at least two SN74LS08N ICs, abbreviated 7408.
The part numbers for 7400 series logic devices often use the following naming convention, though
specifics vary between manufacturers.
 First, a two or three-letter prefix that indicates the manufacturer of the device.
 A two-figure secondary prefix, of which the two most common are '74', indicating a commercial
temperature range device and '54', indicating an extended (military) temperature range.
 Up to four letters describing the logic subfamily, as listed above. In this case it's LS meaning Low
Power Schottky.
 Two or more digits assigned for each device. There are hundreds of different devices in each
family but when this number is the same, the function and pin-out of the chip is nearly always
the same regardless of manufacturer.
 Additional suffix letters and numbers may be attached to indicate the package type, quality
grade, or other information but this varies widely by manufacturer.
So, getting back to our example, SN74LS08N means this is a device made by Texas Instruments (SN), it is
a commercial temperature range TTL device (74), it is a member of the "low-power Schottky" family (LS),
and it is a quad two-input AND (08).
A "pinout" diagram of the 7408 quad two-input
AND is shown at right. You can find similar
pinout diagrams online for other IC devices –
just search on the part number. The notch is
important because it allows us to orient the chip
itself (this is a view of the TOP of the chip). The
gates in the other 74xx series ICs are arranged in
a similar fashion. Pin 14, at the top left, is
labeled Vcc and should be connected directly to
power (the red row, +). Pin 7, at the bottom
right, is labeled GND and should be connected
directly to ground (the blue row, -). All other
pins are for data.
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Circuit Kit Contents
Your kit should include:
 Two SN74LS08N: A Texas Instruments, commercial temperature
range TTL low-power Schottky family, 14-pin quad two-input AND .
 Two SN74HC00N: A Texas Instruments, commercial temperature
range high speed CMOS family, 14-pin quad two-input NAND .
 Two 74HC32AP: A commercial temperature range high-speed CMOS
family, 14-pin quad two-input OR .
 Two CO74HC86E: A commercial temperature range high-speed CMOS 14-pin quad two-input XOR .
 One GD4017B: A Goldstar 16-pin, decade counter. The 4017B is an
integrated circuit that has been designed to count pulses. It can be used in
timing circuits and is often used to switch on and off LEDs or other circuits.
It can be combined with a timer such as a 555 based circuit.
 Two KA556: The KA556 is a dual KA555 made by Fairchild Semiconductor.
The KA556 series dual monolithic timing circuits are a highly stable controller capable of producing
accurate time delays or oscillation. Timing is provided an external resistor and capacitor for each
timing function. The two timers operate independently of each other, sharing only VCC and ground.
 One 7-way or 8-way DIP switch. This contains seven or eight independent ON/OFF switches,
packaged to fit in the same holes as a standard 14-pin IC. When a switch is ON, the two adjacent pins
are electrically connected. When OFF, they are disconnected.
Other Components.
In addition to the breadboard and assorted ICs there are several tools and components we'll need for
our experiments and are included in your set.
Long Nose 5" Pliers.
Power Supply: A 9-volt battery with connector cap. Red is positive/power, Black is negative/ground.
Hookup/Jumper Wire: Wire is needed to make connections between some components. We have a mix
of AWG #22 and #24 solid hookup wire. Numbers higher than AWG #24 indicate wire that will be too
thin to be useful. Numbers lower than AWG #22 is too thick and may damage the breadboard contacts.
Resistor: Resistors restrict the flow of electric current by dissipating heat. Placing a resistor in series with
a light-emitting diode (LED) will limit the current passing through the LED and prevent it from burning
out. The color bands on the resistor denote its resistance. You can look up resistor color codes online.
Light Emitting Diodes (LEDs): LEDs fit easily into an electrical circuit and illuminate
when electrons flow through the enclosed semiconductor material. Our supply
includes an assorted mix of red, yellow, and green LEDs. Important Note: The long end
of the LED should connect to the power source or the data output of an IC. The short
end needs to be grounded. Use a resistor in series (between the LED and ground) to
avoid burning out the LEDs.
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Putting some of it together.
Let's build something simple! First, we'll just test one of the ICs so that we know what we're doing.
1. Look at the pinout diagram for one of the 74xx IC chips.
2. Place the IC on the breadboard so that it straddles the center groove. You now have four extra
holes in the same column as each pin. Use those holes to connect jumper wires in the next steps.
3. Connect VCC (Power Supply -- one of the outer rows labeled by a + plus sign) to pin 14 with a wire.
4. Connect the Ground (one of the outer rows labeled by a - minus sign) to pin 7 with another wire.
5. Choose one of the four gates on the IC to test, e.g. the gate connected to pins 1, 2, and 3.
6. Connect the inputs of that gate (pins 1 and 2, for example) to either VCC or ground, depending on
if you want the input to be a 1 or a 0.
7. Connect the output of the gate (pin 3, for example) to long end of an LED. Ground the LED through
a resistor by connecting the long end of the LED to one end of a resistor and the other end of the
resistor to the - minus sign row. If the LED is very dim, you can skip the resistor.
8. Use hookup wire to connect the two + rows. Do the same for the two - minus sign rows.
9. Put the cap on the 9-volt
The output of AND on pin 8 is
battery and then connect
Connect the two - rows Connect power to
plus sign
1 so the LED lights. The LED
the red wire to the +
pins 9 & 10 making
is grounded with a resistor.
inputs both 1
row and the black wire to
the - minus sign row.
10. Go through all the
possible combinations
for the inputs and
observe the LED
output. For an input of
Connect the
Connect
two + rows
logical 1, connect input
power to IC
to power. For an input
Connect
ground to IC
of logical 0, connect to
ground. In the picture
below, both inputs are
connected to logical 1
Connect the power source, a 9 volt
(power) so the AND
battery, to the breadboard.
gate produces an
output of 1 (power)
and the LED lights up.
Using DIP switches for input.
You can change the input of a gate by moving the wire from the + row
to the – row or vice versa, but this is cumbersome. Instead, use a DIP
switch. Here is a basic diagram for adding the switch. When switch 1 is
OFF, the circuit will be disconnected from the power row and "pulled"
to ground by the resistor, resulting in a 0 input to your circuit. When
switch 1 is ON, the circuit is directly connected to the power row,
resulting in a 1 input to your circuit. To use additional switches as inputs to your circuit, make similar
connections for each switch, with separate power and ground connections and separate resistors.
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Building a Half Adder.
Let's build a half-adder on a breadboard incorporating a XOR gate, an AND gate, two resistors, a green
LED (sum), a red LED (carry), jumper wires, a battery, and two of the switches on the 7-way DIP switch.
Note: In this example, resistors to protect the LEDs were accidentally left out of the circuit. With a newer
battery, and depending on how the ICs are connected, the LEDs can easily burn out unless they are
connected in series with a resistor.
FIRST ROW OF THE TRUTH TABLE:
SECOND ROW OF THE TRUTH TABLE:
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THIRD ROW OF THE TRUTH TABLE:
FOURTH ROW OF THE TRUTH TABLE:
Now that you know what you're doing, go build something useful, like a full-adder, comparator,
multiplexer, decoder, shifter, or even a subtractor. (Okay, just do the circuit you have been assigned.)
References and Sources
Information and text on breadboards from www.play-hookey.com by Ken Bigelow.
Information on LEDs from electronics.howstuffworks.com.
Information about specific ICs from http://upgrade.kongju.ac.kr/data/ttl/.
Part numbering scheme from http://en.wikipedia.org/wiki/7400_series.
A color-coded resistance calculator that looks to be reliable can be found at
http://www.ese.upenn.edu/rca/calcjs.html.
Basic gate function information from http://www.allaboutcircuits.com/vol_6/chpt_7/2.html.
Using resistors at http://www.techdose.com/electronics/How-to-Use-SolderlessBreadboards/252/page4.html
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