The Banggood large screen digital clock kit is an inexpensive kit (A$13 inc case and post).
The clock uses a DS1302 clock chip and microcontroller for display. The microcontroller is a STC15F204EA, a Chinese 8051 microcontroller.
The kit is supplied with Chinese instructions, but a Chenglish version is available online. The only reason I needed an English version is to understand the somewhat obscure setting procedure, but the Chenglish version was not clear about the so-called “timekeeping” settings.
The PCB quality was good, all holes suitable size and clear, and it soldered very well.
The case is very fiddly to assemble. The case is 110mm wide and the very bright digits 25mm in height.
A view of the rear of the assembled clock. The CR1220 cell will be very fiddly to replace due to the screw arrangement used to secure the case parts. I applied a little CA adhesive to the nuts used for the front panel so that the screws could be removed without the nuts falling out… though you must be carefull to not get CA adhesive on the screw threads (lightly oiling them helps).
The performance of these type of implementations depends greatly on the clock chip and the MCU firmware. The clock chip is an old type, a much better choice would be the more accurate DS3231. The firmware is not intuitive, and although easy enough to rewrite the MCU, it is unlikely that revised firmware will become available. The Chinese are the worlds greatest copyists, not respecting intellectual property… and they do not publish their own code as a rule. If this kit was on the shelf at most western hobby shops, GPL code would be available.
A fun little kit to put together on a rainy afternoon… but time will tell whether the accuracy is acceptable.