[ts-7000] Re: Using DIO to switch relays

[Mike Dodd <>]

> > ...the
> > DIO doesn't provide enough current to drive a relay....
> >
> > Initially I need to just turn on an LED, but eventually I need to be
> > able to switch 120 VAC and 24-48 VDC at household-type current
> > draws.
> Just make sure to put a diode in across the load if you use
> a relay or anything with a coil (motor, solonoid).  See this
> article:
> http://www.kpsec.freeuk.com/trancirc.htm
>   

This site has some good information, including an explanation on how to
use a transistor to control the relay. Essentially, you connect a DIO
output through a resistor to the base of the transistor, which acts like
a switch to actuate the relay. And as Dan said, put a diode across the
relay coil to suppress the back-voltage that's generated when the relay
is de-energized and the magnetic field collapses.

Another option would be the TS-DIO24 board. This has three additional
ports, and four bits of port A are open-drain with a 1-amp current-sink
capability. So you could control four DC-coil relays powered by up to
30V. Other ports/bits on this card have fairly high-current sourcing
capability. Four bits can source 48 mA and the 16 bits of ports B and C
can source 24 mA.

But IMO you should read-up on interfacing logic-level electronics to
high-voltage, high-current electrical devices BEFORE you dive in. It is
VERY EASY to destroy a logic board - not to mention injure yourself - if
you don't know what you're doing. If you prefer not to become a
"hardware guy" at least learn about solid-state relays that
have logic-level interfaces. Search the Web, or check Digi-Key or Mouser
electronic suppliers to see if there's an off-the-shelf module that will
directly - and safely - connect to your 72xx board. It will be worth your
time.

Mike

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Mike Dodd - Montpelier, VA

http://www.mdodd.com