🚀 go-pugleaf

In article <801@gold.GVG.TEK.COM> grege@gold.GVG.TEK.COM (Gregory Ebert) writes:
>   In article <3709@uceng.UC.EDU> dmartin@uceng.UC.EDU (Dale Martin) writes:
>   >
>   >I have designed a circuit using ttl logic chips that activates LEDs.  I would
>   >like it to activate some 25W bulbs (one at a time).  What is the best approach?
>   >Could I use relays, or is the switching voltage too low?  How about a transis-
>   >tor?  Aren't there triacs or something that do just that?  
>   >ANY suggestions would be appreciated, the more specefic (part #'s and such)
>   >the better.
>   >
>       There are a few things you can do. First of all, you CAN have common
>	ground for the TTL and the 120 VAC bulbs if you are CAUTIOUS. If
>	you are willing to hunt around, you can get some opto-triacs. This
>	is obviously the safest way to do it. An opto-triac's control side
>	is just an LED, so you have that one licked. The other side is
>	basically like a relay contact if you run it on AC or pulsed-DC.
>	You should put an inductor in series with the light bulb to
>	protect the triac from 'di/dt' problems. A 10uH coil will give
>	you protection up to a di/dt of ~20A/usec (reasonable) for 120VAC.
>	If you use a larger coil, thats OK. Radio Snack sells some $0.79
>	coils that are perfect.

These beasties are actually VERY easy to work with, but they are a bit pricey
(expect about $10 a pop, which I realize can be an issue for a student :-).
They come in various flavors: AC output, DC output, DC input, and (I would
guess) AC input.  They are often refered to as "solid-state relay modules" or
"I/O modules", and most often used in micro-processor based industrial controls
and such (at least that's where I've seen them).  They are small (about the
size of a deck of cards) and modular: can plug in and out of an appropraiate
socket.  I've even seen boards sold which connect up to PC's and allow about a
dozen or so modules to plug in for PC-based control systems. 

If you decide to go the SCR route, I would still suggest using opto-couplers to
the input.  This will isolate your TTL stuff from the nasty AC environment.
This will help out in the "noise" department (trust me, you *DON'T* want to
debug a system which has noise problems!).  Good luck!
--
Disclaimer: All spelling and/or grammer in this document are guaranteed to be
            correct; any exseptions is the is wurk uv intter-net deemuns.

Mike McManus (mikemc@ncr-fc.FtCollins.ncr.com)  
NCR Microelectronics                
2001 Danfield Ct.                   ncr-fc!mikemc@ncr-sd.sandiego.ncr.com, or
Ft. Collins,  Colorado              ncr-fc!mikemc@ccncsu.colostate.edu, or
(303) 223-5100   Ext. 360           uunet!ncrlnk!ncr-sd!ncr-fc!garage!mikemc