七段顯示器：
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| a b c d e f |
b c |
a b d e g |
a b c d g |
b c f g |
a c d f g |
a c d e f g |
c d e f g |
a b c |
a b c d e f g |
a b c d f g |
a b c f g |
判斷共陽極、共陰極的方法：第3和第8腳為COM共同接腳。
方法一：利用三用電表
方法二：利用電源供應器
七段顯示器--共陽極：COM腳固定接+5V
七段顯示器--共陰極：COM腳固定接地
從BCD編碼到七段顯示器：
共陽極：COM腳固定接+5V，輸出為0（L）-LED亮。輸出為1（H）-LED暗。
| 輸 | 入 | 共 | 陽 | 極 | 七 | 段 | 輸 | 出 | 顯 | ||
| A | B | C | D | a | b | c | d | e | f | g | 示 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | |
| 0 | 0 | 0 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 1 | |
| 0 | 0 | 1 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 0 | |
| 0 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | 1 | 1 | 0 | |
| 0 | 1 | 0 | 0 | 1 | 0 | 0 | 1 | 1 | 0 | 0 | |
| 0 | 1 | 0 | 1 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | |
| 0 | 1 | 1 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | |
| 0 | 1 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | |
| 0 | 1 | 1 | 1 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | |
| 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 1 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | |
| 1 | 0 | 0 | 1 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | |
從BCD編碼到七段顯示器：
共陰極：COM腳固定接地，輸出為0（L）-LED暗。輸出為1（H）-LED亮。