Re: [CAD_CAM_EDM_DRO] parallel port signal to relay

Dave:

I-R Crydom (and other makes) do a Solid State Relay ("SSR") which has an
input-signal acceptance of 3-28 volts. At 5 volts, the current-in is maybe 5
mA. So, you can "fire" this SSR with one of the data-lines of the parallel
port (other to ground). Part Numbers for the Crydom SSR's indicate the
voltage and current of the load. For example, a D4840 means DC input, 480
volt AC load @ 40 Amp. Or, A2410 means AC 90-280 VAC in, 240 V. 10 amp load.

They also make "similar" potted DC relays, but I have NO experience with
these.

A TIP-120 would require that there be SOME connection of the printer-port
line to the load, IF that would only be the "equiv." diode of the
transistor's base-collector. I would prefer some 74HCTnn gate be used
"between" the printer port and the TIP-120. Better, some kind of
opto-isolator such as 4N27, but that would then require a separate DC supply.


Remember! MOST PC's have the "printer port drivers" right on the
mutha-board, and often soldered-in, so, if you [delete-] up, you can waste a
whole computer's mother board, or at least get yourself HOURS of very careful
dissassembly and UNsoldering practice! WHich will PROBABLY result in
considerable destruction of the solder-traces/pads, at least!

Jan Rowland, Old Troll


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