Ttl Logic Level Tester Pen.

Polarity Tester Pen & TTL Logic Level Tester Pen.
This polarity tester pen is slightly different because it is able to test TTL levels and shows the status on a 7 segment display using with the letters: “H” (High) for logic level “1” and “L” (Low) for logic level “0”.
In this instructables I will show you how to build one.”

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