The MBED libraries for the stm32f042 use an 8Mhz external crystal or the internal 8Mhz cristal. As the internal one was not good enough at all for timekeeping I added an external crystal in revision 0.2. For that I used the common 3.2*2.5mm crystal.

Only to find out those are only available in 12Mhz or higher...

So I made a revision 0.3 with a 3.2*5mm crystal footprint, in case someone wants to build one themselves. I have not ordered these as I hacked on the 5*3.2mm crystal and I can live with that. All the other issues have been fixed in revision 0.2 and the clock has been working wonderfully the last few weeks.

I will add instructions how to build one and a binary for the clock very soon :)