I second the reccommendation that a 555 and a 4017 decade counter be used.
Hint: use a small ceramic cap and a large >500k ohm resistor. You can use a ceramic or mylar cap and a variable 300k resistor and a 0-200k variable resistor. This will make the 555 clock at a variable rate depending on the position of the variable resistor.
You could also have luck with a >1M ohm resistor and a varaible cap.
I have done this before.. ..and I told myself to remember the order of the pins on the 4017, the pin order is not linear around the chip.
-SF
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