The SNTP synchronised clock (ssc) is an ESP8266 based time of day clock with an LED display.
Code development progresses and a working prototype exists with three display options.
Directly supported 4 digit 7 segment LED displays
Several common driver boards are supported directly by the source code, most of these and variants can be purchased online for small money.
Above is a large 4 digit 7 segment LED display (1.2″ or 30mm) using the HT16K33 driver chip.
Not very expensive at around $20, this might be a Chinese knock-off of an Adafruit display. These are available with a colon for time formatting. Brightness adjustment from firmware is supported.
Above is a 0.56″ 4 digit 7 segment LED display using the TM1637 chip, costing around $5. These are available with a colon for time formatting. Brightness adjustment from firmware is supported.
See the notes at Fix for a certain TM1637 LED display.
Above is a 0.56″ 4 digit 7 segment LED display using cascaded 74HC595 shift registers, costing around $5. I have not seen these with a colon for time formatting. Brightness adjustment from firmware is not supported.
The code has facility to adjust to dim the display in low light (for supporting display types). The prototype uses a PT333-3C phototransistor from D7 to ground, and a 220k pullup resistor from 3.3V to D7. The activation threshold is around 5lux, and can be adjusted by selecting a different pullup resistor.
Two pins offer selection of daylight saving adjustment, and MM:SS display which can be useful for setting other clocks. Both can be controlled by a switch to ground and a pullup resistor to 3.3V.
All boards require few wires, thought eh74HC595 requires one more than the others. The HT16K33 uses I2C so the bus could be shared with other I2C peripherals, no real advantage in this application though.
The first two options are good and have a colon for time formatting. The need to remove the caps on data and clock lines for some TM1637 boards may be a significant disadvantage to some hobbyists.
A work in progress…