I think the old ZN1034 precision timer chip was good for this sort of thing. Not sure if it's still available, but may be worth a look.
J^n
Countdown time switch
Nov 26, 2008
24 Replies
The CMOS version of the 555 - the 7555 - can do this sort of time.
The last time I looked, RS Components had a huge range of timers. Sorry I can't be more specific.
No doubt Lord Armstrong offers a hydraulic equivalent too, or something new-fangled with the power of steam. No need to be so retro as to use a 555.
Besides which, a 555 will be an abysmally unpredictable timer over hours and a 7555 even worse.
In the end, I went for the following timer, which is quite a nice little unit...
formatting link
it from CPC (did find it a bit cheaper elsewhere, but it was too easy to just add it onto an existing CPC order).
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