This document provides instructions for building a circuit using a 4511 BCD-to-7-segment latch/decoder/driver IC to drive a 7-segment LED display. It describes the parts needed, including the 4511 IC, 7-segment display, resistors, switches and battery. The objectives are to learn how to use the 4511 IC to display decimal numbers based on a 4-bit BCD input and gain familiarity with 7-segment displays and displays. The instructions explain how to connect the circuit and experiment with different input values to light up the display segments and also explore the additional inputs on the 4511 IC.

1. 7-Segment Display
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:

2. 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.

3. 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.