Re: [CAD_CAM_EDM_DRO] Parallel Port/Relay Problems... more

Chris Clough wrote:

> Ok - so I went and got all new components and rebuilt it twice now today
> - I'm using the schematic of off Tim's site - I built it, had two EE's
> look at it, and said that's the way it is on the page so... what's my
> next option?

Well, the problem is probably the parallel port. The various chips used
on various motherboards and plug-in cards have subtle differences.
If you have a printer which senses a voltage at the input pins, it works
almost all the time. But, if you want to deliver more current to something
like a SSR or opto-isolator, then it is a different matter. Most
opto-couplers
need 3 mA to guarantee operation of all units. (Some need as much as
10 mA.) Most SSRs need about 10 mA, some more than that. You
won't get that out of parallel ports, in general.

I have used some mini Omron SSRs driven by a parallel port with good
success. I supplied external +5 V to the SSRs + input, and connected the
SSRs - input to the parallel port.

Jon