[Cliff]

It seems pretty clear that manuafacturers like to preserve the screen trigger out for their the more expensive

projectors. Even though it would cost less than a pound to include a 3.5mm socket!

Anyway, I wanted my screen to be controlled by my HW10 and dreamt up this this rather simple, and if I might say elegant, solution.

I purchased an Intelliplug suitable for a desktop computer. This costs around £15.
I used a small mains adaptor which is plugged into the intelliplug and this goes on and off at the same time as the projector.
It gives 12v out and is wired to the the screen trigger.

Works really well and is cheap!

If you do try this at home there are a few small points.

i) Use a 6 to 9v adaptor as a 12v with no load will usually give out a higher voltage.

ii) The adaptor I used kept its voltage a while after switch off so the screen did go up immediately. I used a 470 ohm resistor as a load. You could use a small lamp or just wait if you don't mind the screen going up a few minutes after the projector turns off.

iii) I did put in a series resistor (2.2k) just for protection to limit currents in case something wasn't right. Not strictly necessary but that's just me!

iv) Make sure the polarity is correct. The tip of the 3.5mm plug is usually positive.