So here is a breakdown of what the Datong offered:
- Either Mixed, letter or number combinations
- Groups of 5 characters
- Variable speed ( up to 37.5 word per minute)
- Variable character spacing (up to 4 seconds)
The Datong also allowed you to connect a telegraph key, and your headphones. But for now I will focus on the code generation element of the project.
The finished project has just a handful of components and can easily be created on a breadboard, or indeed if you have an old broken Datong you can reuse the box and panel to really replicate the old kit. The complete project includes 3 variable resistors (1K LIN) for Character speed, gap and volume. It also needs a 3 way switch to select the mode.
The Arduino I’m using is the UNO. Arguably the most popular Arduino on the market, but I have also tried the sketch on a Nano and it works fine – just some customisation of pin assignments is all that is needed.
On start up the Arduino checks to see which switch is LOW – it also saves the current mode and checks if the saved mode is the same as the current selected switch. If this is different, then the Arduino has had a change in the mode selection and resets.
When generating the tones, the Arduino randomly selects a character from an array. With that chosen letter – it calls a function and plays the corresponding tone functions. 2 functions exist as a DIT and a DAH.
The rest of the functions are dedicated to allowing the speed and gap to alter and also displaying the results on the LCD panel (completely optional).
Here is a short video of the kit working, and a link to the source code.