Timezone clocks

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Participants Katje
Skills Electronics, PCB design, Programming, Networking, TCP/IP, NTP.
Status Active
Niche Electronics
Purpose Fun


I thought it would be a fun idea to have some clocks above the entrance way between the main space, and the aux space.

Feature wish list:

  • NTP based time, so as to avoid need to change clocks to keep time or for DST.
  • LED based displays (Easy to use/see)
  • 24 hour clock.
  • KISS design that doesn't solely rely on funky code to work.

Basic design thoughts

Example 7 segment display

74HC4543 driver chip, this allows latching of input so all 4 or 6 digits needs just 4 data pins, and 1 pin per digit for latching.

Design questions?

4 digits or 6?

Having 5 clocks with seconds displayed where sink may not be spot on perfect could really jar. Maybe have a 6 digit version for local time, with 4 digit display for the others?

45mm or 56mm ?

Which micro?

Arduino pro mini is cheap, small and should have enough grunt, but could be an interesting challenge getting TCP/IP, NTP, Timezones, DST, and clock functionality all in 2k of ram.

Techwolf12: ESP8266-12 is very cheap (around 6 euro), is programmable by Arduino and has buildin Wifi.

Wired or wifi?

We'll need wires to power it, so ethernet + PoE may be the simplest solution?

Techwolf12: When using the ESP, you will need 3.3v.


Which timezones to use?

  • Boston/New York - EST (UTC-5:00) / EDT (UTC-4:00)
  • London - UTC / BST (UTC+1:00)
  • Amsterdam - CET (UTC+1:00) / CEST (UTC+2:00)
  • Baikonur - (UTC+6:00)
  • Sydney - AEST (UTC+10:00) / EDST (UTC+11:00)

Bigmac says: I deal with San Francisco, Johannesburg and Manila, can we have those too please? And New York instead of Boston? And Seoul or Tokyo for completeness?

Which timezones could be a long debate, if we're not careful we could end up with 24+ clocks on the wall. Increasing to 7 clocks would allow inclusion of SF and Seoul. Downside is each clock is going to cost about €20, plus prototyping costs.

Alternative timezones:

  • Vandenberg - PST (UTC-8:00 / PDT (UTC-7:00)
  • Cape Canaveral - EST (UTC-5:00) / EDT (UTC-4:00)
  • Amsterdam - CET (UTC+1:00) / CEST (UTC+2:00)
  • Baikanur - (UTC+6:00)
  • Tanegashima - JST (UTC+9:00)


Have created an initial draft idea for a design. Schematic: File:LEDClock-sch.pdf

It's based on a 74hc137 3 to 8 multiplexer, and a 74hc4511 BCD to 7 segment decoder. Will test proof of concept with 0.56" displays.

3d Render of clock design

Prototype Parts

  • 0.56" 7 Segment Displays - ORDERED, DESPATCHED, DELIVERED (Aliexpress)
  • 74HC137 - To order (EOO)
  • 74HC4511 BCD-7 Segment Driver - ORDERED, Awaiting Dispatch (Aliexpress)
  • Resisters - Stock item in the space
  • Breadboards - Stock item
  • DS3231 RTC Module - ORDERED, DESPATCHED, DELIVERED(Aliexpress)

Final Design parts

  • 57mm Common Cathode 7 Segment LED Display (6-4 per clock)


An idea has been suggested that members of the space may want to sponsor a clock (speed of project is going to be dictated by availability of funds). The cost of a single finished clock will be about €20 per clock, depending on exchange rate and whether it works first time...

Sponsors so far:

  • Bigmacfoobar
  • Katje
  • Redlizard



Schematic design complete, parts ordered to produce prototype. Prototype PCB for 4 digit version based on 0.56" displays designed. Courage still needed to hit the order button...


Crazy idea discussed on the mailing list.