Wow. Thanks Thomas. That helps a lot.

Looking over this, I started wondering if it might be possible to actually
trigger the relay using voltage from tablet's audio jack. I've seen people
do this with cell phones and camera flash triggers, although I doubt I can
get 5V DC out of the audio jack without amplifying it...or I find a relay
that can go off 600mV or whatever I can get from the jack.  I'm probably
stuck using an iPad, since my wife has one i can use to build the prototype
and iOS has a pretty good barcode reader library.

b,chris.


On Mon, Nov 19, 2012 at 4:38 PM, Thomas Bennett <[log in to unmask]>wrote:

> On our 3M self checkout, the desensitizer is activated when the barcode is
> read (by a laser scanner) if I remember correctly, the patron is already
> logged in to the system.  You might be able to get something from an
> electronics store to first, replace the manual switch with and electronic
> switch that operates on 5 volts(I think it is 5 on USB), then some how have
> this connected maybe with a usb hub that the scanner is on.  There may be
> other
>
>
>
> From reef central forum:
> The voltage supplied by a usb host or powered hub is between 4.75 and
> 5.25VDC. USB 2.0 specifies 5VDC @ 500ma max.
> The relay you would need would be a 5VDC relay, with the contacts rated
> for 110 -125VAC. These are available, however the load rating is often low
> ~1 amp or less. (not all inclusive)
> Small 1A SPDT Relay, 5v, OMRON
> http://www.allspectrum.com/store/small-1a-spdt-relay-5v-omron-p-512.html
>
> Also from reef central:
>
> I have all the parts to build a USB AC power center, but haven't gotten
> around to trying it.
> The problem here is that a USB port is a serial port.
> While you MIGHT be able to get away with just wiring up one USB serial
> line to a relay and forcing that pin high, you can only do one device.
> My design uses the DALLAS 1-wire switches and a USB adapter.
> You can string together hundreds of these devices onto just TWO wires and
> drive and query all of them using a Linux file system called OWFS ( One
> wire file system ).
> All of the devices on the interface show up in the linux filesystem as
> files.
> To read the status, you just read the file, to change the device status (
> closed or open ) you just write to the file.
>
> Honestly the simplest way to experiment with this stuff is to use a
> computer parallel port.
> You have a LOT more pins and they can be set via peeks/poke from the OS.
>
> Another option is a USB to parallel port converter or a USB relay board.
> http://www.virtualvillage.com/usb-po...stamp-bs2.html
>
> Also check these guys out:
> http://bb-elec.com/welcome.asp
>
>
> Hope this helps,
>
> Thomas
>
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> On Nov 19, 2012, at 4:09 AM, Chris Fitzpatrick wrote:
>
> > Hi,
> >
> > I'm working on designs to build a self-checkout kiosk for our Koha
> system.
> > Seems pretty straight-forward except the book desensitizer part.  All the
> > desensitizers I've every used only had an on/off switch.
> > Has anyone ever seen or used a desensitizer that can
> > be programautomagically triggered?
> >
> > Hoping to use an iPad or Nexus, so something that's not windows only
> would
> > be ideal, but looking for anything right now...
> >
> > thanks for any pointers/suggestions....
> >
> > b,chris.
>