Hi outsider,
Thank you for your reply.
The kind of load will vary, maybe a lamp, maybe a remote relay, maybe a buzzer. I probably should have explained better but I am trying to control things which will be some distance from the arduino (ie on the end of a cable) and coming from a auto electrician background it is frowned upon to have live cables when the devices are off, normally have one ground wire and lots of control wires which go live to turn on the devices. I am trying to stick with this (there is some good reasons why not to use ground switching).
That appears to make it hard to use a NPN transistor. Using a PNP looks like it will do the job but inverts the output making things unnecessarily confusing as I would like stick with "on" (or high) being "on" on the programming side. It also makes it easier to test the functions on a breadboard with leds before connecting to the devices without remembering off is on.
I figure there must be some driver IC's or modules, like the UNL2003, which don't invert the output? This would have the added bonus of not damaging the arduino if you make a mistake with the output as the module/driver may act as an isolator.
Thanks
JD