7 segments display

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The 7-segment displays are displays that allow you to view a figure or a number using luminous segments. The light sources are internal. It is almost always this type of display which is used on radio clocks when the color of the digits is green or red. 

The 7-segment displays mostly emit a red or green light, but there are also some that glow in the blue.

to display a number between 0 and 9, at least seven segments are needed, and these segments have been conventionally assigned the first seven letters of the alphabet: A, B, C, D, E, F and G.


Common anode:

Here is the principle of common anode displays: (Diagram of the inside of the box)



To use its displays, you must always follow the instructions for supplying the LEDs. the (+) of the power supply on the anode and the (-) on the cathode.

Just like the LEDs, you will need to add a resistor (220 ohms if the power supply is equal to 5v) to reduce the current on each segment of the display.

Otherwise you risk toasting the segment.

Common cathode:

Here is the principle of common cathode displays: (Diagram of the inside of the box)


As you have noticed, this time all the cathodes are connected together.

Presentation of the package

The 7-segment displays are on a DIP 10 type. The DIP format governs the spacing between the different pins of the integrated circuit as well as other constraints (presence of heat exchanger, etc.). .



 Decoder for 7-segment display

The (BCD / 7-segment) decoder can be used to control a 7-segment display.

It has 7 outputs, denoted a, b, c, d, e, f, g each corresponding to one of the 7 display segments also denoted a, b, c, d, e, f, g. 

The "a" segment is obviously connected to the "a" output of the decoder and turns on or off depending on the electrical state of the output (on if high level, off if low level).

the inputs are a minimum of four. Note the four main inputs E3, E2, E1, and E0. They represent the binary number E3 E2 E1 E0 (E3 being the most significant bit and E0 the least significant) to be displayed.

The state of the decoder outputs depends on the binary number that we have as input. This binary number is displayed in decimal on the 7-segment display.

With a 7-segment display, only the first 10 digits from 0 (0000 in binary) to 9 (1001 in binary) can be displayed. If the decoder input number is greater than 9, the display no longer represents a number and depends on the type of decoder.





for example the 7448 is a decoder, it has an active logic level at 1 at output.

 


truth table of Output logic levels from Ic 7447 to 7 segments display :








sources:

http://www.zpag.net/Electroniques/Diode/Aff7SegDes.htm
https://www.robot-maker.com/forum/tutorials/article/41-composant-les-afficheurs-7-segments/
http://www.simulog.free.fr/decodeur.htm



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