I can tell you that if you want to advance one of these clocks in your
house hours at a time by remote control, all you need to do is work some
CW in the basement. :D
-Adam
On 3/17/2014 2:38 AM, Nick wrote:
Being fair, this clock was designed a long long time ago when stuff
directly connected to the mains was not so frowned upon - Mike is a
professional engineer and his page is covered with notes recommending
that isolation transformers are used - he readily admits that today,
he would never design a clock like this.
There is pretty much no immunity from mains-borne noise in the circuit
- if you have anything at all noisy on the same ring/whatever, your
clock will run fast or the noise will cause all sorts of other
exciting issues.
The circuit absolutely must have 100n ceramics for each chip (standard
practice anyway) instead of just the couple it uses, and the 5V supply
is derived direct from the mains via a 4V7 zener/100uF, i.e. no noise
filtering there either. The 50/60Hz mains input is current limited by
2Mohm and then the ESD protection of a 4013 used as a buffer is used
to clean the signal a bit.
Nuff said, really.
Personally, I'd never recommend someone build this circuit - there are
far better & safer ones out there.
Nick
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