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

In article ,
Rob Convery wrote:
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

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.

--
*Can vegetarians eat animal crackers?

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" wrote in message
...


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


Dave Plowman London SW
To e-mail, change noise into sound.

Rob Convery wrote:
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


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.

"Dave Plowman (News)" wrote in message
...
In article ,
Rob Convery wrote:

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.

--
*Can vegetarians eat animal crackers?

Dave Plowman London SW
To e-mail, change noise into sound.

I am guessing you are talking about
http://www.velleman.be/common/produc...?lan=1&id=9317

I 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

"dennis@home" wrote in message
. uk...
Rob Convery wrote:



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




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

"Rob Convery" wrote in message
...

"dennis@home" wrote in message
. uk...
Rob Convery wrote:



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




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



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.

In article ,
"dennis@home" writes:
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.

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.

--
Andrew Gabriel

"Andrew Gabriel" wrote in message
.. .
In article ,
"dennis@home" writes:
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.

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.

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

In message , Rob Convery
writes
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.

Is it really worth it?

The rest of the screen won't be illuminated anyway

--
geoff

"raden" wrote in message
...
In message , Rob Convery
writes
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.

Is it really worth it?

The rest of the screen won't be illuminated anyway

--
geoff

Er yes if the screen opens 100% then due to it being 4:3 and having a 45cm
top border it will go down to a a couple ft from the floor and would look
down right stupid. By stopping the screen at the 16:9 point with around a
20cm top border it sits perfectly over the LCD and just above the centre
speaker.