Precision Clock Mk IV

Original Article ↗ Hacker News Discussion ↗

Overall reception

  • Strong enthusiasm for the write‑up and the project as a whole; many readers praise the depth of the design narrative from requirements to shipping product.
  • Several people treat it as more of a functional art piece than a practical clock, but still want one; some already own earlier versions and report excellent experiences.

Price & availability

  • Price (~£250–350) is a sticking point for some, though others compare it favorably to high‑end consumer gadgets.
  • First batch sold out quickly; at least one commenter mentions an “instant impulse buy” and another already assembled a Mk IV successfully.

Display, flicker & high‑speed cameras

  • Initial concern about photosensitive epilepsy is resolved: each digit is multiplexed at ~100 kHz with analog (non‑PWM) brightness control, well above problematic flicker ranges.
  • Discussion clarifies the difference between segment update rate and PWM brightness control, and why analog driving gives flicker‑free images even under high‑speed cameras.
  • Some confusion about “88” smearing is attributed to camera exposure/rolling shutter; later high‑speed footage shows clean millisecond digits.

GPS time, accuracy & timezones

  • GPS discipline is highlighted: the local oscillator drift spec only matters during GPS loss; with 1PPS wired to interrupts, two clocks can be synchronized to tens of nanoseconds in good conditions.
  • Debate over whether more exotic references (chip‑scale atomic clocks, rubidium modules) would be “cooler,” versus their much higher cost.
  • Auto‑timezone from GPS and onboard timezone database is widely admired, though some want manual overrides or fixed UTC/alternate‑zone modes, especially for ships or secure facilities.

Hardware design & EMI / compliance

  • Some are impressed by the two‑layer PCB with one near‑continuous ground plane; others argue the EMI‑reduction claims are unrealistic given ground plane cuts and layout.
  • There’s extended discussion of EMC testing requirements, CE/FCC costs, and the legality/practicality of self‑declaration for small‑run hobby products.
  • Micro‑USB choice is mildly criticized; others note USB‑C could be done with just resistors but might be harder to assemble by hand.

Feature requests & use cases

  • Requested for a future Mk V: Ethernet + NTP or PTP (esp. for datacenters/SCIFs), Wi‑Fi, manual timezone selection, external displays (e.g., I²C), solar power, and even onboard atomic oscillators.
  • Actual use cases mentioned include synchronizing high‑speed video of fast processes and serving as a lab or homelab reference display.