Electric Projector Screen Control Module

[Rob Convery]

Wondering if anyone knows of any little electronics module that would control my projector screen for me from my projector trigger output. Due to my screen being a 4:3 but only using it as a 16:19 it means that i only need to power the screen for X seconds to bring it down far enough for the projector.

I am looking for something that will function such as

Normal Relays OFF

0v -> 12v Trigger from Projector Trigger Relay 1 for X seconds (240v) then off 12v -> 0v Trigger from Projector Trigger Relay 2 for X seconds (240v) then off

Anyone know of any companys that make suitable modules without spending £100s

Cheers

Rob

[Dave Plowman (News)]

Maplin VF08 at 14.99. Accuracy is +/- 3 seconds, though, but it would probably be able to improve on this for a specific application (as it will time up to 60 hours) by using low leakage capacitors for the RC circuit and a fixed rather than variable resistance.

You'll need a suitable box (they recommend VY40) and a 24 volt at 50 mA AC power supply.

[Rob Convery]

You got a URL - VF08 does not seem to return anything using maplins search.

[dennis]

How about a couple of microswitches and a couple of holes in the edge of the screen?

You make a momentary connection across the switch to start it and it stops when the hole allows the microswitch to open.

[Rob Convery]

I am guessing you are talking about

have had a quick look at it and this just appears to be a module that will turn something on for a set amount of time. I am not quite sure how this would solve my problem as how would the signal going from 12v -> 0v trigger be used to trigger the second relay?

Ah - thinking of two independant circuits - Two trigger relays connect to the 12v projector triggger. One relay the K6200 is connected to the Normally open contact, the other relay the a K6200 is connected to the Normally closed contact.

ie. 12v triggers down then 0v triggers up

Rob

[Rob Convery]

I don't fancy cutting holes in a £400 screen which could affect the way it hangs (ripples etc) - things like that invalidate the warrranty :)

[dennis]

OK. How about magnets and reed switches (you may need a relay or two too).

Put a couple of magnets on the screen where you want it to stop and use the reed to break the connection when the magnet gets there.

[Andrew Gabriel]

One way which is used for this sort of thing is to monitor the motor current, which typically increases when the transport hits an endpoint, top or bottom. It also has the advantage that the motor drive is cut if the thing jams mid-way. You need a limit timer too, incase that fails due to some sort of gearbox failure or the current sense not operating correctly. The current sense might need overriding for the first half second or so when the motor starts up, or to incorporate a half second delay in the current sense which can be more useful if the transport presents a varying load on the motor.

[Rob Convery]

The screen already has built in protection circuits like you describe. The main problem or me was the timered part due to not wanting to bring down the whole screen