Projector Dowser

[Andrew Edwards]

I was thinking about being able to dowse a projector without DMX. A button on a string is obviously also a solution but still requires an additional cable run not to mention having to actually press it.

I then thought about would already be there to utilise. Many CAT5 senders also have audio via a mini-jack so I then thought perhaps a dowser could be adapted to respond to a specific audio signal sent down this likely unused line.

 

So a dowser controlled by a audio tone being sent down the audio line of a cat5 sender, triggered from a spare output from your AV cueing software/hardware of choice. No DMX required and a doddle to program.

 

Any takers or thoughts on whether existing dowsers could be adapted?

[Jevans]

We tried that but with a slightly different application (our dowsers are DMX) - the remote for the projectors can either be IR or it's got a 3.5mm jack output that can be directly plugged into the projector. We tried sending that down our CAT5 extender but it wasn't having any of it unfortunately - I suspect the remote didn't output enough power to make it over the CAT5 cabling.

 

I'm not aware of anything that would do audio tone -> DMX (or at least, not in the way you want) so I think it would be a custom job, perhaps using a simple RC/LC filter network to differentiate between two different tones without having to resort to digital trickery?

[timsabre]

perhaps using a simple RC/LC filter network to differentiate between two different tones without having to resort to digital trickery?

 

If you just use presence/absence of signal you could send a square wave using a 555 timer and detect it at the other end with a bridge rectifier turning on a transistor.

[Jevans]

True, true - you could then send a square wave from QLab or similar too straight into the extender so you could cue it, assuming you got the levels right.

[alistermorton]

Indeed I suspect that's basically what the mobile phone app "TriggerTrap" does to trigger cameras/flashes , as without the dongle you can hear your phone chirp when it triggers.

[themadhippy]

Some slide projector from days of old had the facility to advance with a tone, if you can find one of those your half way there

[Brian]

Send an LF tone of 50Hz down the line to the projector, feed that into a cheap audio power amp and use the speaker output to drive an AC relay.

[sandall]

I've met mechanical dowsers using paddles & stepping motors, but I find a cheap 5.8GHz IR extender kit & the projector's remote control works just fine for blanking the output, & also allows you to switch sources, or freeze the output while changing presentations (VERY useful for the sort of conference where you only get the USB stick as the speaker is being announced).

[kitlane]

I've met mechanical dowsers using paddles & stepping motors, but I find a cheap 5.8GHz IR extender kit & the projector's remote control works just fine for blanking the output, & also allows you to switch sources, or freeze the output while changing presentations (VERY useful for the sort of conference where you only get the USB stick as the speaker is being announced).

 

Blanking the output on many projectors is not the same as placing a physical shutter in front of the lens. Depending on the projector you will still get the sickly faint glow of the lamp projected on the screen and this is plenty bright enough to ruin a blackout.. Some projectors are better than others, and some have a mechanical shutter built in which could be controlled by your method. However, plenty of the lower end projectors don't.

[sandall]

Blanking the output on many projectors is not the same as placing a physical shutter in front of the lens. Depending on the projector you will still get the sickly faint glow of the lamp projected on the screen and this is plenty bright enough to ruin a blackout

True - it's a while since I used projection in a show (it's mostly corporates these days) & I missed that OP is a theatre man.