Re: Pixie error connection

Tom,

I am still struggling with an interface between a Pixie 100 and a
sound logic breakout board. I have just failed to get ULN2803 to work
properly. It does cause the Pixie to error when I connect the ground
and without the ground connection, it does not trip the estop relay.
Tom and the designer of the break-out board have suggested that this
chip would work. I have connected Pixie as described below.

The Estop on the breakout operates the coil of a relay so draws about
.04 amps. I connected the signal ( 5v ) from Pixie error out to pin 1
and Pin 18 to the estop +5v terminal. Pin 9 to gnd to the estop gnd.
Connecting ULN2803 gnd to Pixie ground did pull the Pixie to an error
condition.

I don't understand the description about needing to wire the relay
control between the Darlington package ground and the Pixie ground and
wire a single Darlington output to Pixie +5vdc.

Thanks,

Keith Clark

Tom wrote:

>
> The ULN2803 would do the job for the relay but you cannot wire it as
> recommended if you don't want the Pixie to perceive an error. Normally,
> the relay controls would be between the Darlington collector and Pixie
> +5vdc and the Darlington ground would be wired to Pixie ground. This
> would draw most of the current from the pullup resistor and cause the
> ERROR voltage to drop to a level that may be detected by the Pixie as a
> fault.
>
> So you would probably need to wire the relay control between the
> Darlington package ground and the Pixie ground and wire a single
> Darlington output to Pixie +5vdc. A diode is not needed since the solid
> state relay does not actually have a coil.
>
> Tom Hubin
> thubin@...
>