Re: [Gumstix-users] Line voltage relays...

[Arthur M. <ar...@ar...>]

Hi Peter,

Relays are nice for switching mains power, as they keep the mains 
circuit electrically separate from the gumstix. Less chance of frying 
your gumstix or doing the I've-found-the-live-wire dance.

Which relay you use isn't that critical, just make sure it can carry 
enough mains current for your application. To energise the relay can 
take a bit of power, more than a standard TTL output gives. The relay 
spec. will tell you what current it needs. You can supply this current 
using a transistor switch. Here's a nice Linux friendly example ;-)

http://www.linux.com/howtos/Coffee-3.shtml#ss3.2

See 3.2, Controlling with a relay. Connect a gum output where the 
example says parallel port data pin. The gumstix then controls the 
transistor switch, which will open and close the relay.

The diode across the relay is important. When you switch off the relay, 
the relay coil will deliver a negative inductive kick. The diode short 
circuits this kick. Without the diode, the transistor might be damaged.

I like the auto-blinds idea. You could link it to the heating system 
too, and have a complete intelligent house! Okay, maybe I'm getting 
carried away here.

Happy building,

Arthur


Peter Greis wrote:
>>>2. Has anyone interfaced a gumstix to line voltage
>>>relays/switches (230v) ? Which parts are you using
>>
>>?
>>
>>I haven't, but I've long thought about trying to
>>power a gumstix  
>>setup inductively from next to a 110 or 220v power
>>line.  I think the  
>>applications for an inductively powered gumstix
>>would be really cool.
> 
>  
> Nice idea, but I really meant "could I control some
> sort of relays"? For example, we have a (large) panel
> of switches that control our external blinds going up
> and down (common feature here in Switzerland). It
> would be very slick to replace this with a touchscreen
> and the necessary relays (solid state or otherwise).
> Any idea where to buy relays of this type ?
> 
> As for my bluetooth question - the walls here are cast
> concrete (or blocks). This makes it really hard to run
> cabling... so within one room (or down the hallway)
> bluetooth is probably sufficient for the gumstixen to
> coordinate between themselves.
> 
> Thanks for all of the input,
> 
> -P
> 
> Peter Greis
> Zurich Switzerland
> 
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