With this very simple technique, we can can generate all ASCII numeric characters and most ASCII alphabetical characters with a 7 segment LED display and with a minimum of components (1N4148 diodes) . This can be useful for example, for visualizing the position of a rotary switch, the selected input of an audio preamp, the current state of an electronic device, alarm etc. In most cases, a small number of characters are required which makes the circuit very simple.
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Step 1: Example for Numeric ASCII Characters
Step 2: Circuit Diagram for 0-9 Numeric ASCII Characters
Step 3: Examples of Alphabetical ASCII Characters
Additionally, we can generate a large number of symbols.
Step 4: Generating One Single Character
For a single ASCII character, we don't need the diodes at all.