A Morse Code Message Pendant
Morse code, while first developed in the 1800s, remains a viable way to send short text messages with a minimum of components. The challenge here is that a relatively small number of people know how to interpret such text encoding, which on the other hand would also make it a great way to share info between you and another specific person.
One might even use it to transmit a sweet message for Valentine’s Day — next year. If you’d like to get a jump on things, Technoblogy’s David Johnson-Davies has an interesting messaging solution in the form of his Morse Code Message Pendant.
This little charm employs an ATtiny10 microcontroller to send out a blinking light message via an onboard LED. If you want to make it even more secret, you could use an infrared LED, which would make the message invisible to the naked eye, but viewable via a mobile phone’s camera.
Despite the ATtiny10’s minuscule 1,024 bytes of flash program memory, the device is able to store and transmit over 100 words — hopefully well enough space to get your point across.
Code along with the board design is available in the project's write-up. As noted there, the code works by looking up the different characters on a program message string, and translating them into a series of "dot" and "dash" LED pulses. The post also goes over the hardware setup, as well as how to make a convenient pogo pin programmer for it.