Lightning Talk Timer

Details

Based on a discussion at Hackaday Europe 2024 the idea was born to build a 7-minute timer for the Sunday lightning talks. Based on this, a brainstorming resulted in the following list of features:

7-minutes countdown timer
Blinky
Visible for speaker and audience
Easy to read
Alarm (1 minute left)

Initial idea was to use a 7-segment display on four sides, but later a custom 5x7 matrix was designed to be more flexible with the animations and functions. The timer was designed in Fusion 360.

Full function is shown in this video (12x faster):

The timer is powered by a USB powerbank, mounted to the inner structure. There is a service opening at the top to access the controller, reset button and USB cable for charging.

The timer was successfully used for the Sunday lightning talks at Hackaday Europe 2025.

Project Logs

Collapse

Software
makeTVee • 05/10/2025 at 12:06 • 0 comments
The code is running on a XIAO nRF52840 Sense board using Zephyr RTOS (VS Code with nRF-Connect). It is my first Zephyr project, so still learning.
- Peripherals:
The LED animations are running in the main thread, the Servo control and timing for the alarm mechanism is in a separate thread triggered when the 1 minute is left.

Sourcecode: https://gitlab.com/maketvee/ltt_zephyr
I used some pixel art tools to test animations and also generated tome GIFs for my Lightning talk about the timer at HdE.
Alarm mechanism
makeTVee • 05/10/2025 at 12:06 • 0 comments

The alarm mechanism was designed to be triggered once per countdown. A steel ball sits in an upper compartment and falls down as soon as the slider is moved by the servo. The ball hits an old phon bell in the middle of the mechanism and falls down into the lower compartment. The compartments are now closed again. When the clock is flipped for restarting the countdown, the ball is also flipped and now the lower compartment is the upper compartment. So flipping the timer is also rearming the timer, and no additional energy is needed to move the ball, just gravity.

The servo is triggerd at startup and 1 minute before the countdown ends. All parts are custom designed and 3D printed.
5x7 LED panel
makeTVee • 05/10/2025 at 11:50 • 0 comments

The 5x7 LED panel PCB was designed in KiCAD with 5050 WS2812B LEDs
The PCB is mounted at the back of a 3D printed diffuser using two layers of white PLA as a diffuser.
The pixels are separated with black PLA. Printing is done with color change, so the outer layer is one closed surface.After some first fails, the white PLA was interweaved into the black PLA by enlarging the second layer. This leads to a robust solution and the white PLA stays in place even when pushing on it directly with the finger.