Anyone old enough to fondly recall the “bleep-burp-rattle” sequence of sounds of a modem negotiating a connection over a phone line probably also remembers the simple “tin-can telephone” experiment, where a taut string transmits sound vibrations from the bottom of one tin can to another. This tin can modem experiment puts both of those experiences together in a single project.
As [Mike Kohn] notes, this project was harder than it would seem that it should be. He actually had a much harder time getting the tin can phone part of the project optimized than getting the electronics sorted out, resulting in multiple tries with everything from the canonical tin cans to paper coffee cups before eventually settling on a pair of cardboard nut cans, the kinds with the metal bottoms. Linked together with a length of kite string — dental floss didn’t work — [Mike] added a transmitter on one end and a receiver on the other.
The transmitter used an ATtiny 2313 and everyone’s favorite audio amplifier, the LM386, while the receiver sported an electret mike preamp board, an LM566 tone decoder, and an MSP430 microcontroller. The modulation scheme was as simple as possible — a 400 Hz tone whose length varies whether it’s a one or a zero, or a stop or start bit. Connected to a pair of terminal programs, [Mike] was able to send his name over the wire string at what he calculates to be six or seven baud.
This project has all the hallmarks of lockdown boredom, but we don’t care because it’s good fun and a great learning opportunity, particularly for the young ones. There’s plenty of room for optimization, too — maybe it could even get fast enough for the Hackaday Retro 300-baud challenge.
Apparently, the plan is to build a giant clock so he started off by making the first digit. To keep it cheap and simple the segments are made from corrugated cardboard which was carefully cut, folded, and then glued together. The light-diffusing lid is simply made from white paper. He used the ubiquitous WS2812B strips to light up the segments, but things turned out to be more complicated as he was not able to get enough strips to fill up all the segments. This forced him to cut up the strip into individual pieces and space them out by reconnecting the LEDs with wires. Cutting, stripping, and soldering 186 wires took him almost 10 hours. An Arduino Uno serves as the brains of the device and there is a nice Android app to control it via Bluetooth.
