Recently my YouTube channel unexpectedly started to get attention, so I decided to do something special for when it finally reached 1,000 subscribers. An internet-connected live counter seemed like a great way to celebrate the event, with the added bonus that other people could build one themselves. There are already a few excellent split-flap kits out there so I came up with a mechanical 7-segment display.
I designed, printed, and tested a single segment first. It’s a relatively simple concept. The segment needs to cycle through 10 states; while it’s being actuated each state should be held for as long as possible before flipping over to the next. The states are encoded as knobs on timing gears, and these are different for each segment. A bi-stable spring helps with a crisp flip between states. Also, the segments “fold away” — instead of just rotating 90 degrees, they hinge around two pivots to hide the yellow display surface against the wall of the case. The entire CAD was done in Fusion 360, and everything can be printed with a standard FDM 3D printer.
Driving it with a single stepper motor appealed to me as an elegant, minimalistic solution. I also designed a custom circuit board to tidy everything up. The board is a minimal ATmega328, a Darlington driver array, and a Hall effect sensor, which drive the motor, register the current position after power up, and communicate with the next digit in the chain via serial. A Raspberry Pi gets the current count from the internet.
I also made each digit modular; when another digit is needed some time in the future, it can just be plugged in at the end.
Get the printable files on Cults3D