BCD to 7-segment decoder
| 4511 | BCD to 7-segment decoder |
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| Technology: CMOS | Power supply: 3-15 V | 16-pin DIL |
 Pin connections |
Other inputs |
| Truth table |
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Basic operation |
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The function of a BCD to 7-segment decoder is to convert the logic states at the outputs of a BCD counter such as the 4510 into a form which will drive a 7-segment display. The display shows the decimal numbers 0-9 and is easily understood.
The individual segments making up a 7-segment display are identified by letters as follows:
There are two important types of 7-segment LED display. In a common cathode display, the cathodes of all the LEDs are joined together and the individual segments are illuminated by HIGH voltages. In a common anode display, the anodes of all the LEDs are joined together and the individual segments are illuminated by connecting to a LOW voltage.
The 4511 is designed to drive a common cathode display and won't work with a common anode display. You need to check that you are using the right kind of display before you start building.
When the 4511 is set up correctly, the outputs follow this truth table:
BCD inputs |
segment outputs | display |
|||||||||
D |
C |
B |
A |
a | b | c | d | e | f | g | |
0 |
0 |
0 |
0 |
1 | 1 | 1 | 1 | 1 | 1 | 0 |  |
0 |
0 |
0 |
1 |
0 | 1 | 1 | 0 | 0 | 0 | 0 |  |
0 |
0 |
1 |
0 |
1 | 1 | 0 | 1 | 1 | 0 | 1 |  |
0 |
0 |
1 |
1 |
1 | 1 | 1 | 1 | 0 | 0 | 1 |  |
0 |
1 |
0 |
0 |
0 | 1 | 1 | 0 | 0 | 1 | 1 |  |
0 |
1 |
0 |
1 |
1 | 0 | 1 | 1 | 0 | 1 | 1 |  |
0 |
1 |
1 |
0 |
0 | 0 | 1 | 1 | 1 | 1 | 1 |  |
0 |
1 |
1 |
1 |
1 | 1 | 1 | 0 | 0 | 0 | 0 |  |
1 |
0 |
0 |
0 |
1 | 1 | 1 | 1 | 1 | 1 | 1 |  |
1 |
0 |
0 |
1 |
1 | 1 | 1 | 0 | 0 | 1 | 1 |  |
There is a question about whether the 6's and 9's should have tails. The 4511 produces a display without tails. If other binary values, greater than 1 0 0 1 are connected to the inputs of the 4511, the outputs are all 0's and the display is blank.
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In normal operation, the lamp test and ripple blanking inputs are connected HIGH, and the enable (store) input is connected LOW. The circuit diagram shows the 4511 and a 7-segment common cathode display connected to the outputs of a 4510 BCD counter:
To build this circuit follow the prototype board layout from the 4510 Beastie Zone web page and then add the 4511 with connections to a third prototype board, as shown below:
This is a complex prototype layout. The best way to get it to work is to build it up in stages, checking that each subsystem works before going on to the next.
Don't forget - 
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Connect pin 16 of the 4510 and 4511 to +9 V and pin 8 to 0 V.
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When the lamp test input, pin 3, is made LOW, all the segment outputs go HIGH regardless of all other input conditions.
With lamp test HIGH, if the ripple blanking input, pin 4, is made LOW, all the segment outputs are forced LOW. This input can be used to blank leading zeros in a multi-digit display.
The enable input controls the action of a 4-bit latch inside the 4511. With enable LOW, the outputs of the latch follow the logic states of the BCD inputs and the 7-segment outputs change accordingly. If enable is made HIGH, the logic states present on the BCD inputs are stored. The 7-segment outputs remain unchanged until enable is made LOW once more. This action allows the display to be updated at intervals.
When you need these inputs, you can work out how to use them by investigating the behaviour of the 4511 in a prototype circuit.
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4511 datasheet from 
Cross references in the Beastie Zone: 4510 BCD counter, 4518 dual BCD counter.
Cross references in Design Electronics:
External links:
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