Michael Black wrote...
No, that's why Exar introduced the 2240, which was a 555 (though without
some of the pins externally available) in a package with a 7-bit binary
counter. Via feedback you can set the divider to whatever you want,
and then you run the 555 at a decent rate. As people have pointed out,
you can then adjust the clock almost immediately, and you don't fuss
with the impossible of getting suitable components for such low timing
rates.
I have no idea if the 2240 is still available.
Exar's XR-2240 was second-sourced, often with the same part number.
Plus there was Fairchild and TI's uA2240, and NSC's LM2240. In
the old days you could find one of these at suppliers like Jameco.
I looked and didn't see any, so perhaps it's the end of that era.
In the back of my mind I think there's a similar chip... Aha, yes
now I remember, it's Intersil's icm7240 series, also made by Maxim.
These are still available. For example, the popular ICM7242 is an
8-pin chip with a 555-style oscillator driving an 8-bit divider,
see
http://www.intersil.com/cda/deviceinfo/0,1477,ICM7242,0.html
To finish the story, there are some other single-ICs using the
'2240 '7240 oscillator-plus-counter idea, but without the classic
relatively-precise 555-style oscillator. Examples are the CD4060
or 74HC6060, the mc14536 or mc4541, plus Philips' 74HCT5555, etc.
These use a different type of simple CMOS relaxation oscillator.
Unless you succumb to the PIC crowd :>), you may want to explore
a two-chip solution, which allows higher oscillator frequencies.