seven-segment L.E.D. display.
A seven-segment display may have 7, 8, or 9 leads on
the chip. Usually leads 8 and 9 are decimal points. The figure below is a
typical component and pin layout for a seven segment display.
SEGMENT DISPLAY
The light emitting diodes in a seven-segment display
are arranged in the figure below.
DIODE PLACEMENT IN A SEVEN SEGMENT DISPLAY, NO
DECIMAL
There are two types of displays available, common
anode and common cathode.
The wiring for a common anode is shown below.
COMMON ANODE INTERNAL WIRING
The wiring for the common cathode is shown below.
COMMON CATHODE INTERNAL WIRING
To convert the binary numbers to signals that can
drive the L.E.D.s in the display you need a display driver. In the lab we use
an MC14511 chip. The pinouts are shown below. U17MC1451112345678910111213141516BCLTBILEDAGNDedcbagfVcc
PIN OUTS FOR THE MC14511 SEVEN-SEGMENT DISPLAY DRIVER
A, B, C, and, D are the binary inputs.
a, b, c, d, e, f, and g are the driver signals to
the display elements.
LT is the Light Test control, turns all segments on,
active low.
BL blanks all the segments when activated, active
low.
LE is the latch enable control.
The truth table shown below is used to confirm that
the digital signal sent to the display lights up the correct segment.
TRUTH TABLE FOR THE SEVEN-SEGMENT DISPLAY
The internal circuitry and logic gates for the
display is shown below.
INTERNAL CIRCUITRY AND LOGIC GATES FOR 7 SEG DISPLAY
The specific seven-segment display used in lab is an
LN513RK. The schematic below is similar to the one you will use in lab.
SEVEN SEGMENT DISPLAY WITH DISPLAY DRIVER
To have the driver convert the binary input to
signals ready for the display, tie pin 3, LT, and pin 4, Bl, to VCC. Connect
pin 5, LE, to ground. In this configuration what ever the binary inputs at A-D
are will be converted and the display will show the decimal equivalent.