Re: [CAD_CAM_EDM_DRO] Re: Simple Parallel Port controller

In a message dated 02-Sep-01 10:28:33 Central Daylight Time,
sariddle@... writes:

> My biggest question is are there 2 pins on the pp that I
> can hool to to get my switching for the relay? And if so what kind of
> power consupmtion requirments do I need to stay under for the relay
> as to not damage my pp? Do you have any sample code for just turning
> off and on one pair of pins?
>
>

Scott: Lemme try: Pins 2-9 of the DB-25 (the PPP "printer cable plug" on
the rear of the PC) are the 9 data-bits. Pins 18-25 are (usually all
connected) ground. I think pin-18 is ground even when the lazy vendor has
not connected them all together. So, for ONLY two pins, a "ground" and a
"hot", choose pin-18 and pin-2, respectively. Then, my example-lines in
BASIC, already given to you,

10 OUT 888,1
                 30 OUT 888,0

will turn pin-2 "on" ("HI") in line-10, or "off" ("LO") in line-30.

Power? Not much! You might "squeeze" 5 mA from a pin. So, you MUST use
some kind of solid-state relay, or "pre-driver". This can be as simple as a
good NPN transistor (pref. Darlington) with at least a 1K or 1K5
base-resistor to the pin-2.

I would not dare to propose to give you a schematic of what I mean, as, well,
the reasons are too detailed for the scope, here. At the risk of sounding
like an impatient old teacher, "If you can't take it from here, you haven't
any business messing with the PPP, as you WILL damage your computer!"

Jan Rowland



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