Re: gEDA-user: Power relay question

[John Doty <jpd@xxxxxxxxx>]

On Jul 28, 2011, at 7:03 PM, DJ Delorie wrote:

> 
>> Or 4000-series CMOS logic. Nice thing about 4000 series in this
>> application is that it can operate on unregulated 12V.
> 
> I thought of that, but a linear regulator just for the pic would be
> cheap, and you get debounce, multi-input state machines, and a
> watchdog for no extra cost...

Simple state machines and debounce are easy with MSI, too, and you don't need a software development setup. Arguably easier to debug a simple MSI circuit than a program.

> 
> Even if I ran a 4000 right on the 12v, I wouldn't count on that 12v to
> be very clean if it has motors running off it.  Electrically braking a
> motor with an H-bridge can spike the power rails.

4000 series is extremely resistant to noise on the power rails. I've run it off raw stepper motor power, no problem. I think that's really its remaining niche: slow logic running on noisy raw power.

> 
> And a pic + regulator (sot-26 + sot-323) is probably going to be
> smaller than the equivalent 4000-series chips anyway.

If you use a 12V H-bridge you need level translation, too. That's sometimes annoyingly expensive in one way or another.

> 
> But of course, there are zillions of ways of doing it, it's up to the
> designer to pick what's best for their needs.

Agreed.

John Doty              Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd@xxxxxxxxx




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