On Thu, 06 Nov 2008 15:45:43 -0600, John Fields
wrote:

On Thu, 6 Nov 2008 19:17:04 -0000, "IanW" wrote:


"John Fields" wrote in message
. ..
On Wed, 5 Nov 2008 14:46:46 -0000, "IanW" wrote:

"John Fields" wrote in message
m...
Just for fun...

Hi John. Is pin 11 of U1 supposed to go anywhere, only it's not connected
in
the diagram and the circuit doesn't work.

---
U1-11 is a spare, so its output is supposed to float.

In which way does it not work?

It doesn't light up at all. I better check the wiring though as with all
those diodes the wiring on the breadboard got a bit fiddly!

---
A "gotcha" I noticed yesterday, or the day before is that, wired the way
it's shown, (with the register outputs sinking current) if all the
register outputs come up reset on power-on, then there won't be enough
current to turn on all the LEDs and you'll have to wait for an entire
cycle before the thing starts to chase properly. If you've got the pot
set to "full slow" that could take about 30 seconds, so it might be
working, but since nothing was appearing to happen it looked like it
wasn't working.

In order have it start right away the shift register outputs should
_source_ current, so I fixed the circuit and attached a copy of the new
schematic.

BTW, with the pot set at midpoint, the thing ought to shift at about a
1Hz rate.

Also, here's a simulation of both ways (sink and source and 8 bits,
only, but you'll get the point, I'm sure.)



The twentieth LED does not have a 1N4148 compliment to it like the
others.