[HH] cheapest/simplest way to control a relay from a PC

[Nuno Sucena Almeida]

On 11/08/2012 02:18 PM, Tom Metro wrote:
> relay control boards, but I'm thinking a TTL compatible reed relay, like:
> http://www.nteinc.com/relay_web/reed.html
> 
> wired to the parallel port (the server has one, and it is unused), and
> controlled with some software, like parashell:

Those relays as you say are 5V min TTL compatible, did you check if your
parallel port provides those voltages? Some 'newer' ones , specially
laptops, give 3.3V, but since you are talking about a desktop it
shouldn't be the case; a multimeter is your friend.
The other concern is current draw: the first of those relays has typ.
coil resistance of 200Ω , which would imply 10mA. It seems a bit high
for a parallel port, which would require the transistor buffer that you
mention.

Honestly I feel that the opto-coupler solution would be simpler and less
prone to mechanical failure and noise.

Cheers,
Nuno

-- 
http://aeminium.org/nuno/