🚀 go-pugleaf

jg3o+@andrew.cmu.edu (Jason Ari Goldstein) writes:
>The subject pretty much says it all.  I need to switch some light
>switches with TTL signals (I am building a controller for my
>fraternities dance floor lights).
>BTW, I have looked into solid state relays but $17-$25 each is way too
>much.  So, if someone could send me a circuit diagram or point me to a
>good book (especially for triacs) it would make me very happy.

They're cheaper surplus; Hosfelt Electronics (1-800-524-6464) has a 10A
opto-isolated solid state relay for $9.95, and an optoisolated 2.5A relay
for $2.59 (which could be used to switch individual lights).  They have no
minimum order.  These aren't "logic gate" relays, however, and probably
need more input current than LS TTL can supply:  a 7407 or 7417 open-collector
TTL hex buffer with a 200 ohm collector resistor ought to be an adequate
translator; on the other hand, my Digikey catalog has some SSRs with 3-30V
inputs that claim to require "1-18mA"; since that presumably means 1mA at
3V, that's a little more reasonable.  LS TTL still won't cut it, but a
74LS125A quad bus buffer will just abut handle it, and a 74LS245 octal bus
transceiver will be loafing (and only costs $.75 from Digikey).

Someone else mentioned that Radio Shack has a Forrest Mims III book that has
a circuit (they even still carry enough parts to build it, too :-).  Note that
if you don't know what you're doing wiring it up, you are better off buying
a commercially prepared unit (unless your fraternity doesn't care about it's
fire insurance -- if a hand-made unit causes a fire, or even looks to the
insurance inspector like it might have, you can forget about the insurance).
If you *do* know what you're doing, it's not too hard to wire it up properly;
just remember to be very respectful of what 10A at 110V can do...