[sdiy] Divide by 10^6?

[Phillip L. Harbison]

flightofharmony wrote:
> I have a question for the logic & digital folk: is there a
> low-component-count, off-the-shelf way to divide down from 20MHz to 20Hz?
> I'm trying to add a clock rate LED to the Sound of Shadows delay module
> prototype I'm working on. A cascade of six 74*90 ICs works fine, but that's
> a lot of board space just to blink an LED.

You could by 0xF4240 (10^6) using 5 74x161 counters. The
TC (terminal count) output would be connected to the PL
(Parallel Load) input and to the clock of a D flip-flop
configured as a T FF (/Q connected to D). This does not
save you many chips but gives you a lot of flexibility.

If you are planning to blink an LED, 20 Hz is a bit fast
for the human eye to recognize. Dividing by 10^7 or 10^8
(2 Hz to 0.2 Hz) is probably more reasonable. To reduce
the chip count,

You could save some chips by using two 74HC4040 to divide
by 2^N where 1 <= N <= 24. Dividing by 2^23 would give a
flash rate of about 1 Hz.

-- 
Phil Harbison