Opto / relay recommendation

I think you want to use a solid state relay of some
kind. Depending on your access to surplus, these can
be very cheap. I use the greyhill odc5 modules a lot.
If you do, the best way to drive it is to turn on the
relay with a logic low level, as it is not reliable to
use logic high. Similarly, you want to connect the
24v to the solonoid, and use the relay to pull the
other end of the solonoid low. The alternative may or
may not work.

You may wish to use a mechanical relay. In this case,
one of the udn200x series darlington arrays will drive
the coil low very nicely. You can use the relay to
interrupt ground or power. Don't forget to bypass the
coil with a diode.

Either way, it would be good to get relays that will
withstand 24v on the coil side so you can use the same
power supply for both ends.

Eric

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