Rotary dials are one of my favourite UI devices. I like the force feedback they provide as you spin a number in, and the sound they make as the dial zips back into position. At last, I can have that feeling every time I make a call, using Polish engineer Paweł Zadrożniak's crazy DiY rotary dial smartphone.
Zadrożniak writes on his blog that this bluetooth-enabled rotary dial is the perfect "useless invention" that's all about hipster nostalgia. He even built it with a hipster battery:
The device is based on Nordic Semiconductor nRF51422 chip (NRF51 DK board). It is recognised as a bluetooth keyboard, so no additional software is required. All you need is a phone with Bluetooth 4.0 Low Energy (BLE) support. The firmware is a modiffied HID keyboard example from the SDK, so it took me only about an hour to add a rotary dial support. The dial itself which generates the pulse dial signal was taken out of an old phone. The board could be powered from a 3V coin cell battery, but I have connected a large, flat, 4,5V battery because small coin batteries are not hipster enough!
If you want to make one of your own, Zadrożniak has helpfully provided the source code.