Re: Introduction

> A friend of mine asked to take a look at the
> list, so here I am. That friend is Tim Goldstein.

You mean TG has time to make friends? Hey TG you've got no time to
socialise, we've got work to do :)

> I am in the process of
> building a cnc flame/plasma cutting machine. I am using Camtronics 5 amp
> controller and Desknc. Everything is moving accurately, but I am unable

to

> trip a solid state relay for the cutting O2. I am getting a signal from

the

> parallel port, but it must not be enough current to pull in the relay. I
> applied 5 volts from the logic portion of the controller board and

measured

> the current. It only takes 7ma to pull in the relay. Any suggestions on
> how to pull in the relay from the signal on the parallel port? I am not

an

> electronic genius, so the simpler the better.

Dave, if I understand correctly, you are applying a permanent ground to the
relay and the positive is being produced by a parallel port pin. This did
not work so you provided the positive from the logic 5v and it was OK.
The problem is that the parallel ports "high" output is from what is known
as an open collector with high pull up.What this means is that the output
chip on the parallel port does not connect its output between the 5v rail
and the 0v rail to represent a high and low - instead it will connect the
output to the 0v rail for a "low" but for a "high" it will switch its output
off or open circuit.
This does not give you a 5v output for "high" .
There is a resistor of between 4.7k ohm to 10kohm between the output and the
5v rail so that when the output turns off the resistor allows external
circuitry to "see" the 5V rail but draw very little current from it.
Therefor you may get as little as 1/2 ma thro the resistor.
The proper way to use this is to use the weak current 5v signal to drive a
higher current device that does not need much current to switch it - e.g a
transistor.
You may be able to things backwards if you can configure your software to
send a low instead of a high to signal an O2 start,
you can take a permanent 5v logic supply to the relay and switch the Ov -
the parallel port can "sink" more current than it can supply.
If this is gobbledegook, I can explain more off -line.

Mo