BCD decoder and 7-segment display
A 4-bit binary number goes into a 74HC4511, which works out which of the seven segments to light for that digit. The display is seven LEDs with a common cathode, each with its own current-limiting resistor.
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How it works
Switches 1–4 are the bits D0 (worth 1), D1 (2), D2 (4) and D3 (8).
| D3 D2 D1 D0 | digit | segments |
|---|---|---|
| 0 0 0 0 | 0 | abcdef |
| 0 0 0 1 | 1 | bc |
| 0 0 1 0 | 2 | abdeg |
| 0 0 1 1 | 3 | abcdg |
| 0 1 0 0 | 4 | bcfg |
| 0 1 0 1 | 5 | acdfg |
| 0 1 1 0 | 6 | cdefg |
| 0 1 1 1 | 7 | abc |
| 1 0 0 0 | 8 | abcdefg |
| 1 0 0 1 | 9 | abcfg |
| 1010–1111 | blank | — |
Try it on the bench
- Set the switches to 0101: the display shows 5.
- Try 1010 (ten): the 4511 only does decimal, so it blanks the display.
- Select the display and set its resistors to 0 Ω (bare LEDs): the segments burn out. Every segment needs its own resistor.
Parts on the bench
- Bench power supply
- DIP switch module
- 74xx4511
- 7-segment display
In the course
Zen’s Electronics Design Mastery, module “Digital Electronics”.