Mailbox Alarm

Here’s a 555-based project that can be used as mailbox alarm. By suitable mounting of the LED and the phototransistor, the circuit is able to detect when a letter is dropped in your mailbox. Our younger readers should know that a ‘letter’ is not the result of hitting any of the A-Z keys on the PC keyboard, but a precursor of the email message. For some mysterious reason, some people are still sending messages to each other using letters.