RE: DIO writes..

From: Eric Hudson <ehudson_at_midlandhome.net> · Date: Sun, 3 Apr 2005 14:03:41 -0500

Thanks, this should take care of the hardware connectivity and I should be
able to do the rest with comedi.

Eric

-----Original Message-----
From: comedi-admin_at_comedi.org [mailto:comedi-admin_at_comedi.org] On Behalf Of
Daniel Nilsson
Sent: Sunday, April 03, 2005 10:55 AM
To: comedi_at_comedi.org
Subject: Re: DIO writes..

On Sat, Apr 02, 2005 at 11:07:24PM -0600, Eric Hudson wrote:
> I'm using Measurement Computing PCI-DAS6034 and I want to know if I can
send
> 5V out of a DIO pin to turn on a relay. I'm trying to turn on a buzzer
> connected to a relay that accepts 5VDC and 110VAC. If this can't be done
as
> described above how may I achieve this?

>From looking at the spec on your card, the DIO outputs are rated at
32mA but will at that voltage only give you between 3.8V and 4.2V
output. Depending on the type of relay, this may not be enough
current to make it operate.

In addition, again depending on the type of relay, the control input
of the relay might be connected to a very inductive element (a coil)
that will result in a voltage spike when the current is turned
off. These voltage spikes might damage your DAQ card if you connect
the relay directly to the DIO output.

To solve both potential problem, make the DAQ card DIO output control
a transistor that in turn controls the relay. Put a diode across the
relay so that the voltage spikes are taken care of.

-- 
Daniel Nilsson

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