Re: Cascading two 74LS90's doesn't work (needs deglitching)

Rocky wrote:

I am using two 74LS90 ICs cascaded in series to divide down a clock
signal (f=1/60 Hz). A 74LS90 has a divide by 2 and a divide by 5
section in it. The 1min period clock pulse is therefore divided up
into:
2min, 5min, 10min and 25min periods.

the 2, 5 and 10min periods work OK, but the 25min doesn't. It turns
out to also be 10min rather than 25min.

You'll need less parts and it would be more flexible and more stable with a
microcontroller. I've implemented it to test the PIC12F508, which I've
bought some time ago and it works well, the internal oscillator is very
accurate. Instead of a rotary switch, I'm using 4 buttons: If you push one
button, it is displayed with a LED and the other LEDs are turned off.

Just for fun I've routed it (no wonder for such a simple circuit, it is
possible with one bottom layer, only, without bridges) and rendered it with
Eagle3D:

http://www.frank-buss.de/PICPulseGenerator/index.html

--
Frank Buss, fb@xxxxxxxxxxxxx
http://www.frank-buss.de, http://www.it4-systems.de
.