FreeBSD and controlling an alarm via relay

[Ian Smith]

Hi Achilleas,

Dropping multimedia@ cc as this seems pretty well 100% hardware .. but 
I'm not subscribed to hardware@ so please cc me from there.

On Wed, 6 Jul 2011, Achilleas Mantzios wrote:

 > another thing that puzzles me is power.
 > This board : http://www.ebay.co.uk/itm/USB-Eight-Channel-Relay-Board-RS232-Serial-Controlled-/110710333092?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item19c6d99ea4
 > needs VDC 12V supply 
 > while this one : http://www.ebay.co.uk/itm/USB-Four-4-Relay-Module-Board-Home-Automation-/180646300804?pt=LH_DefaultDomain_0&hash=item2a0f5bcc84
 > is self powered from USB.
 > 
 > batteries do not come cheap, and having an extra AC/DC adaptor is not very good either ...

That 4-relay one might better suit your application then, if FreeBSD usb 
recognises it.  It seems to use the same (FTDI?) drivers under windows 
as the other one, but I know almost nought about USB device detection.

 > another thing is the relay parameters, i see various figures :
 > Relay parameters: 5V / 72mA, 15A/24VDC (120VAC), 10A/250VAC or
 > Each switch 12VDC/15A or 240VAC/10A or
 > Open (No) and Closed (NC) Contacts rated for voltages: 12VDC/15A; 24VDC/15A; 125VAC/15A; 250VAC/10A
 > 
 > my specific application i want to drive is this wireless xmitter :
 > http://www.visonic.com/Data/Uploads/MCT_100_Installer_Guide_English_DE2241U.pdf
 > Should i assume my device that i want my relay to control will have voltage of 3V?
 > 
 > for which Voltage/Ampere figures should i opt? are those figures crucial?

5V / 72mA is the relay solenoid drive current.  4 of these switched on 
would use ~300mA, leaving 100mA for the other board circuitry.  The 12V 
board's relays use the same drive power, 360mW, ie 12V @ 30mA.

The relay switched contacts are rated at 12VDC to 15A (180W) or 240VAC 
to 10A (2.4kW!), whereas your MCT 100 is only watching for NC contacts 
to open; closed circuit current will be a few mA at most and you won't 
see more than 5V over the open contacts .. ie, not an issue.

 > thanx a lot

A pleasure.

cheers, Ian