controlling screen with PJ trigger

Thank you, Don. It appears that the Sony VW12HT trigger does not even accomplish 60 mA. The manual says that the trigger delivers only 12V but no current - which sounds like utter nonsense in physical terms to me: how can you have a potential difference without current???


I will now try this guy which I was told has a reel resistance of 800 Ohm and should trip with a current of 14.2 mA... I will let you know if that works!


Best regards and happy new year!


AAG


PS: I just found that the trigger has "4.7 kOhm output impedance". Sigh! It sounds like I still won't be able to trip my relais...

aag-


In situations like this, you will need to control the relay thru a NPN transistor. The base of the transistor will connect to the trigger output thru a 2.2K ohm resistor. This will limit the base current to 5 mA. The collector of the the transistor will connect to one end of the relay coil. The emitter of the transistor will connect to ground, along with the negative side of the 12v trigger. The other side of your relay coil will connect to a 12VDC source (wall transformer). I would also consider placing a diode across the relay coil, cathode side to +12V, in order to protect the transistor from the back emf that is generated from the coil when it is de-energized.


If this all sound too confusing, then I can send you a diagram.


Best-


Don

Dear Don


i now tried to tie in a 800 ohm Finder relais, still to no avail. The LED on the relais' mount lights up indicating coil tension if the relais is unplugged. Soon as you plug the relais into the mount, the LED stops lighting. Voltmeter readings confirm that the current from the Sony is insufficient.


Hence yes, I would be infinitely grateful if you could give me some directions as to how to proceed. I think that I understood the concept of what you wrote: the transistor would work like a high-impedance primary relais, which would then allow current (provided by a wart transformer) to drive the secondary Finder relais.


However, I need to know what the specs of such a transistor would be. If unavoidable I will take on soldering but I am utterly untalented at that. If it is possible to buy the transistor in some kind of box with wire attachment screws I would be much happier...


thanks

AAG

Hi AAG.


I had the same problem with a Sony HS51 and Dalite screen. I bought a low current relay (about 30 mA if I remember correctly) and the Sony still couldn't trigger it. I did something similar to what Don describes, basically inserted a transistor to trigger the relay, all contained in a little box behind the screen. I think I put together a PDF for this for some other guy with the same issue. I'll check my office computer on Monday and see if I still have it. Let me know if you're interersted.


(see this post http://www.avsforum.com/avs-vb/showt...08#post5367508 )


Why they put such weak triggers on these, I'll never understand.


Best regards,

Nas

Ok guys, hard to believe - but I made it!! After burning the first IC, I managed to get everything up & running upon second attempt. And I only sacrificed 25% of my weekend to get there...


Now the screen nicely goes down when the Sony starts up, and goes up again when the projector stops cooling (not immediately after shut down - sigh!).


My only complaint is that the screen is rather slow. Behind the screen is a window, and behind the window (across the street) is the Embassy of the People's Republic of China, which therefore becomes illuminated by my projector for ca. 30 seconds before the screen is down... Let's see how long it takes until this gets me in trouble!


Here is the scheme of what I have done. I figured I better document this carefully, lest I do not know what to do when the thing stops working!

Quote:
Cost! The manufacturers try to trim cost as much as they can. I have the same issue with my Panny, and I'm sure my Infocus 4805 will be no different.


Congrats on your trigger circuit, aag!


Don