11 February 2020

TIL311 clock and fun KiCad project

PCB travel box :)
While in the past I tried (and not documented) to wire four TIL311 displays on perfboard, I quickly realized the project would need too much wiring to be fun and relaxing. Fast forward a couple of years and a positive experience of PCB design with KiCad, I decided to refresh the whole process.

PCB under vacuum
This time I would design a PCB composed of two detachable parts: one with the logic and another with the display. This way I can choose between two physical layouts and reuse the logic board for other projects, provided a new display or daughter board is designed.

Few requirements for the logic board in order to exploit TIL311 peculiarities:
  • per-digit independent dimming control (needs PWM outputs),
  • per-digit latch control (obviously),
  • common BCD DCBA bus to all displays,
  • independent LED voltage vs logic voltage (to reduce heat generation and thermal stress on TIL311),
  • free form management of embedded decimal points (provide pads on PCB, wire later).
 Further on, from my previous experience as clock builder:
  • interface to common I2C RTC board
  • interrupt driven time base,
  • build-time choice of 1 pps or 32 kHz interrupt from RTC
  • LDR for dimming
  • button + potentiometer to handle user interaction

Click and zoom for details.
This time I ordered 10x PCBs from JLCPCB.com . I chose black finish because I think it matches best the red-purplish displays. I did a DIY panelisation in the sense that I drew a line where it should be cut, and I do it with a cutter if needed. They arrived in a sturdy cardboard box. Click and zoom in the picture to see how the small font has been printed.

And here it is, #1 clock resulting from this project. It turns out that the RTC module doubles as a standoff, so the whole thing stays upright in a nice-looking position for a desk.

A 4x TIL311 clock with Arduino Nano.