AllAboutCircuits — http://www.allaboutcircuits.com/vol_6/chpt_7/9.html

PARTS AND MATERIALS
4511 BCD-to-7seg latch/decoder/driver (Radio Shack catalog # 900-4437)
Common-cathode 7-segment LED display (Radio Shack catalog # 276-075)
Eight-position DIP switch (Radio Shack catalog # 275-1301)
Four 10 kΩ resistors
Seven 470 Ω resistors
One 6 volt battery
Caution! The 4511 IC is CMOS, and therefore sensitive to static
electricity!
CROSS-REFERENCES
Lessons In Electric Circuits, Volume 4, chapter 9: "Combinational
Logic Functions"
LEARNING OBJECTIVES
How to use the 4511 7-segment decoder/display driver IC
Gain familiarity with the BCD code
How to use 7-segment LED assemblies to create decimal digit displays
How to identify and use both "active-low" and "active-high" logic inputs
SCHEMATIC DIAGRAM
ILLUSTRATION
INSTRUCTIONS
This experiment is more of an introduction to the 4511 decoder/display driver
IC than it is a lesson in how to "build up" a digital function from lower-level
components. Since 7-segment displays are very common components of
digital devices, it is good to be familiar with the "driving" circuits behind
them, and the 4511 is a good example of a typical driver IC.
Its operating principle is to input a four-bit BCD (Binary-Coded Decimal)
value, and energize the proper output lines to form the corresponding decimal
digit on the 7-segment LED display. The BCD inputs are designated A, B, C, and D
in order from least-significant to most-significant. Outputs are labeled a, b,
c, d, e, f, and g, each letter corresponding to a standardized segment
designation for 7-segment displays. Of course, since each LED segment requires
its own dropping resistor, we must use seven 470 Ω resistors placed in series
between the 4511's output terminals and the corresponding terminals of the
display unit.
Most 7-segment displays also provide for a decimal point (sometimes two!), a
separate LED and terminal designated for its operation. All LEDs inside the
display unit are made common to each other on one side, either cathode or anode.
The 4511 display driver IC requires a common-cathode 7-segment display unit, and
so that is what is used here.
After building the circuit and applying power, operate the four switches in a
binary counting sequence (0000 to 1111), noting the 7-segment display. A 0000
input should result in a decimal "0" display, a 0001 input should result in a
decimal "1" display, and so on through 1001 (decimal "9"). What happens for the
binary numbers 1010 (10) through 1111 (15)? Read the datasheet on the 4511 IC
and see what the manufacturer specifies for operation above an input value of 9.
In the BCD code, there is no real meaning for 1010, 1011, 1100, 1101, 1110, or
1111. These are binary values beyond the range of a single decimal digit, and so
have no function in a BCD system. The 4511 IC is built to recognize this, and
output (or not output!) accordingly.
Three inputs on the 4511 chip have been permanently connected to either
Vdd or ground: the "Lamp Test," "Blanking Input," and "Latch Enable."
To learn what these inputs do, remove the short jumpers connecting them to
either power supply rail (one at a time!), and replace the short jumper with a
longer one that can reach the other power supply rail. For example,
remove the short jumper connecting the "Latch Enable" input (pin #5) to ground,
and replace it with a long jumper wire that can reach all the way to the
Vdd power supply rail. Experiment with making this input "high" and
"low," observing the results on the 7-segment display as you alter the BCD code
with the four input switches. After you've learned what the input's function is,
connect it to the power supply rail enabling normal operation, and proceed to
experiment with the next input (either "Lamp Test" or "Blanking Input").
Once again, the manufacturer's datasheet will be informative as to the
purpose of each of these three inputs. Note that the "Lamp Test" (LT) and
"Blanking Input" (BI) input labels are written with boolean complementation bars
over the abbreviations. Bar symbols designate these inputs as active-low,
meaning that you must make each one "low" in order to invoke its particular
function. Making an active-low input "high" places that particular input into a
"passive" state where its function will not be invoked. Conversely, the "Latch
Enable" (LE) input has no complementation bar written over its abbreviation, and
correspondingly it is shown connected to ground ("low") in the schematic so as
to not invoke that function. The "Latch Enable" input is an active-high
input, which means it must be made "high" (connected to Vdd) in order
to invoke its function.


SDD notebook, 6 September 2006; original excerpt source: Iguana Labs, http://www.iguanalabs.com/breadboard.htm

Computer Hardware
Using the
Breadboard
(Socket Board)
The bread board has many
strips of metal (copper usually) which run underneath the board.
The metal strips are laid out as shown below.
These strips connect the holes on the top of the
board. This makes it easy to connect components together to build
circuits. To use the bread board, the legs of components are
placed in the holes (the sockets). The holes are made so that they
will hold the component in place. Each hole is connected to one of
the metal strips running underneath the board.
Each wire forms a node. A
node is a point in a circuit where two components are connected.
Connections between different components are formed by putting their
legs in a common node. On the bread board, a node is the row of
holes that are connected by the strip of metal underneath.
The long top and bottom row of holes are usually
used for power supply connections.
The rest of the circuit is built by placing
components and connecting them together with jumper wires. Then
when a path is formed by wires and components from the positive supply
node to the negative supply node, we can turn on the power and current
flows through the path and the circuit comes alive.
For chips with many legs (ICs), place them in the
middle of the board so that half of the legs are on one side of the
middle line and half are on the other side.
A completed circuit might look like the
following. This circuit is
from our Microcontroller Beginner Kit.
How to use a Breadboard
(Socket Board) – www.iguanalabs.com/...