TUTORIAL ABOUT SEVEN SEGMENT DISPLAY PIN DIAGRAM, INTERNAL CIRCUIT AND HOW 7 SEGMENT DISPLAY WORKS

 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.