» Experiment » Calculator/Converters » Radio » Newsletter » Associations and Societies » Component Manufacturers

 Electronics Symentics A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Microcontroller Intermediate Kit - Using a 7 Segment LED Display with a 2051

The 7 segment display is found in many displays such as microwaves or fancy toaster ovens and occasionally in non cooking devices.  It is just 7 LEDs that have been combined into one case to make a convenient device for displaying numbers and some letters.  The display is shown on the left. The pinout of the display is on the right.

This version is a common anode version.  That means that the positive leg of each LED is connected to a common point which is pin 3 in this case.  Each LED has a negative leg that is connected to one of the pins of the device.  To make it work you need to connect pin 3 to 5 volts.  Then to make each segment light up, connect the ground pin for that led to ground.  A resistor is required to limit the current.  Rather than using a resistor from each LED to ground, you can just use one resistor from Vcc to pin 3 to limit the current.

The following table shows how to form the numbers 0 to 9 and the letters A, b, C, d, E, and F.
'0' means that pin is connected to ground. '1' means that pin is connected to Vcc.

 a (Pin 1) b (Pin 10) c (Pin 8) d (Pin 6) e (Pin 5) f (Pin 2) g (Pin 9) 0 0 0 0 0 0 0 1 1 1 0 0 1 1 1 1 2 0 0 1 0 0 1 0 3 0 0 0 0 1 1 0 4 1 0 0 1 1 0 0 5 0 1 0 0 1 0 0 6 0 1 0 0 0 0 0 7 0 0 0 1 1 1 1 8 0 0 0 0 0 0 0 9 0 0 0 1 1 0 0 A 0 0 0 1 0 0 0 b 1 1 0 0 0 0 0 C 0 1 1 0 0 0 1 d 1 0 0 0 0 1 0 E 0 1 1 0 0 0 0 F 0 1 1 1 0 0 0

Now, we want to run the display with the 2051 microcontroller.  We will use Port 1 to run the display.  Use the same configuration as in the first 2051 tutorial.  Connect the 2051 to the 7 segment display as follows.

2051 pin 12 to display pin 9    (P1.0 will control segment g)
2051 pin 13 to display pin 2    (P1.1 will control segment f)
2051 pin 14 to display pin 5    (P1.2 will control segment e)
2051 pin 15 to display pin 6  (P1.3 will control segment d)
2051 pin 16 to display pin 8    (P1.4 will control segment c)
2051 pin 17 to display pin 10    (P1.5 will control segment b)
2051 pin 18 to display pin 1    (P1.6 will control segment a)

Connect the display pin 3 to 5 volts using a 100 ohm resistor.

A sample program that cycles through the numbers and letters above is 7seg.asm. It is included on the CD that comes with the Microcontroller Beginner Kit.

Compile the program using TASM and load the hex file into the 2051. Put the 2051 into the circuit and connect the power.