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Topic: 74hc595 oe pin not working (Read 1 time) previous topic - next topic

Docedison

#15
Jun 29, 2012, 11:00 pm Last Edit: Jun 29, 2012, 11:12 pm by Docedison Reason: 1
You can get Anything you want... if you know where and in some case's how to ask... Electronics components... Certainly ANYTHING you could find in a catalog... Bare 100W LED's, $26.95, Free Shipping... All Day Long, ( $59.00 with the CC driver )... GREAT Project for an Arduino, a 100 W LED Dimmer, uses a 74HC595 and some small sensing resistors...

Doc
--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard

tmd3

Earlier today, I wrote:
Quote

If you promise to send me the two "bad-out-of-the-box" 74HC595's, I'll tell you how to get the other three to work.


Then some other clown said:

haha, and if you cant figure that out you can send me the other 3 ...


Maybe I'm too sensitive, but I'm thinking that somebody doesn't take me seriously here.

Here's what I think is going on:  you're driving the one LED that doesn't work from pin 9 of the74HC595.  Pin 9 is called "QH'" in this datasheet - http://www.sparkfun.com/datasheets/IC/SN74HC595.pdf - and its function is "serial data out."  The logic and timing diagrams show that it's not affected by OE, and it doesn't have a high impedance state.  If you drive an LED from this pin, you can't control it by pulsing OE.

I think that you want to drive that LED with pin 7, "QH," whose function is "parallel data out #7."  Pin 7 responds to OE just like the other seven parallel data pins.

Did that fix it?  Are you going to send my my shift registers?

Docedison

Good Call Really good. and more likely than my ideas about pull ups (was the mistake I made the most often, thinking that the processor was in a known state and letting it control the bus line instead of insuring that just in case it is in a known state)

Doc
--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard

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