I am looking some design help for a basic relay circuit to control a projector lift I am building. I need it to react to a 12V trigger from the projector. I am stuck on this problem. I have found a remote relay baord that I can do it from an IR signal, but I prefer to use the projector trigger, as I feel it would be more reliable in the long run, and possiblly even easier to build.

If any of you have a schematic that expalains the relays and configuration needed it would be appriciated. I would also buy the board with relays if someone has them made already.

Simple start the motor and the projector on power up, stop when lowered by limit switch, the reverse polarity and raise on projector shut down and stop when raise by limit switch.

Thanks

Mike

I can definately provide you with a relay setup to solve your problem...however you sound like your tech savy yourself so I believe if you check out www.altronix.com you will find your solution in a vast inventory of simple and multifunction relays with trigger inputs that accept 6-12VDC. A simple solution would be to use a simple DPDT Latching relay board with a 12 or 24VDC coil and a 12VDC + or - trigger input that can be directly connected to the 12 V trigger output of the projector (this relay would be used to power TWO polarity reversal relay modules that are controlled by the "raised" limit and the "lowered" limit switches. When in the raised position, a 12V trigger on the relay can only supply the polarity to lower the lift by actuating the "lower" polarity reversal module and visa virsa when in the lowered position. For this to work properly and for long term you would want a quality high current linear power supply which could feed the relays and your motor and you would also want two limit switches on each the raised and lowered positions. One limit for activating one of the polarity reversal circuits and the other limit to reset the latching 12 VDC trigger relay to kill power to the polarity reversal module powering the motor. The next time the trigger is applied to the latching relay the process starts over and feeds your motor the proper polarity to either raise or lower the lift depending on which limit is active. The site www.altronix.com you will find everything you need including a power supply. I hope this info helps, with this kind of setup, you will have a pretty decent lift. I also agree with you that the most stable method is to use the trigger output from the projector eliminating the reliance on IR or RF. Your parts would run under $100 USD and would fit in a small chasis on your lift or away from your lift with the proper wiring.

Scott, welcome aboard. If you don't mind, I'd like to suggest that long posts like yours be broken into paragraphs to make them easier to read, like this:


I can definately provide you with a relay setup to solve your problem...however you sound like your tech savy yourself so I believe if you check out www.altronix.com you will find your solution in a vast inventory of simple and multifunction relays with trigger inputs that accept 6-12VDC.

A simple solution would be to use a simple DPDT Latching relay board with a 12 or 24VDC coil and a 12VDC + or - trigger input that can be directly connected to the 12 V trigger output of the projector (this relay would be used to power TWO polarity reversal relay modules that are controlled by the "raised" limit and the "lowered" limit switches.

When in the raised position, a 12V trigger on the relay can only supply the polarity to lower the lift by actuating the "lower" polarity reversal module and visa virsa when in the lowered position. For this to work properly and for long term you would want a quality high current linear power supply which could feed the relays and your motor and you would also want two limit switches on each the raised and lowered positions.

One limit for activating one of the polarity reversal circuits and the other limit to reset the latching 12 VDC trigger relay to kill power to the polarity reversal module powering the motor. The next time the trigger is applied to the latching relay the process starts over and feeds your motor the proper polarity to either raise or lower the lift depending on which limit is active.

The site www.altronix.com you will find everything you need including a power supply. I hope this info helps, with this kind of setup, you will have a pretty decent lift.

I also agree with you that the most stable method is to use the trigger output from the projector eliminating the reliance on IR or RF. Your parts would run under $100 USD and would fit in a small chasis on your lift or away from your lift with the proper wiring.


See what I mean? Hope you aren't offended. Again, welocme to the forum.

Hello Larry,

No offense taken. I get to typing and get carried away. Have been living in Costa Rica for a few years on Int. Airport Projects. Moved back to NC a few months ago and am getting back into the custom install game. I stumbled onto this forum and enjoyed reading so I came aboard. Thanks for the welcome.

Hey Scott,

Thanks for the help. I have a circuit figured out now. Now I have a new problem. I am getting conflicking info for the technical folks a Infocus about the 12v trigger. My understanding is that the projector will send out a 12v signal while powered up, and turn it off when powered down. However, the Infocus folks said it is a momentary 12v trigger. I would really appreciate it if anyone can clear this up. I am also going to post this as a new thread.

Mike

Why would the state of the trigger matter. Relays exist whose coils require maintained and pulsed triggers. Determine in the field the output of the 12v trigger and order the oppriate relay. I would disagree with the previous advice in this one respect. I believe you should use at least one 3PDT relay so you can interlock the trigger of each relay. I posted a similar question on the Yahoo site and Bruce passed on a link to a 12v site which had lots of cool circuits intended for the car audio market but with different relay coils could be for any voltage. Unfortunately I have the link on my lap top ( I'm on my newly repaired desk top ) which is why I haven't posted earlier.

Alan

Hey Mike,

Your welcome. Don't concern yourself with the momentary trigger out on the projector. Does the relay circuit you have include a latching or (ratchet) relay with a trigger input? If so the trigger input activates the relay and the contacts will stay latched until the trigger input receives a momentary 12 volts again.

Also, your limit switches should be set up to apply the same trigger input to ratchet the relay to kill the motor's power when in whatever resting position raised or lowered. Remember in your design to include the provision to have a set of limit switches just to control the polarity state of the motor and a set of limits to control the latching relay providing power to the associated polarity reversal circuit.

Your limits reset the entire process at the latching relay when it reaches it's resting position and when powering on and off the projector, only power will be applied to the proper polarity reversal circuit becasue of limit switch positions. This will associate powering on to the lower position and powering off to the raised position.

In response to Alan's post...if all the triggers are interlocked, the problem will be that when all relays activat simultaneously upon projector trigger (power up or power down) there will be no synchronization between the lift's position and the voltage polarity to the motor.

Tripple pole relay, Scott. The position of the third pole interlocks the other coil. It does not effect how you suggested wiring the circuit. It only effects how the coil is wired.

Alan

Just don't see the point using TPDT when using limit switches...as you have to control the polarity reversal by limit switches and the polarity modules accept trigger input which is easily accomplished with a limit. There is no purpose to interlock as there is no need to sync relays. Sorry Alan, we also do custom large venue theaters. On wider, heavier accoustical screen curtains we are faced with the exact same issue, only larger motors set up like a slide gate operator using simple limit switches. At UCF learned a unique way for electrical engineers to test a circuit design by having us stand up at a large dry erase board, draw our design in black then apply power in red. Works and gets the techs off the job in the field with stable product.

Hope I didn't offend anyone. Already worked out issues like this post in my career.

One thing to look for is that the trigger will likely not put out enough current to actually close a relay. If this happens, the relay will not close and if you measure the voltage on the relay, it could be as low as a half volt...which will then spring back up to twelve when you disconnect the relay.

I solved this once by amplifying the current, and that took an irritating amount of time.

The second time, I took the trigger voltage, ran an LED with it, bought a Niles light sensor, put the LED next to the light sensor, wrapped the whole thing with black tape, and I got 12 volts out when the projector was on, 0 volts when the projector was off.

For a variety of reasons, the simplest solution is desireable. (KISS). the projo has a built in circuit that provides a rock solid contact closure. Take advantage of it and augment with the most reliable and least complicated solution.

Thanks for all of your input.

I have new news that I would like for someone to confirm. I have heard from an installer that the 12v trigger output on the projector is actually a 12v continuous out while the system in on and 12v off when the system is off.

For a continuous 12v Signal:

The circuit I have designed is very simple. I have employed a DPDT relay that toggles between poles when activated. The continuous 12v holds its postions. It will be at one pole when no trigger is supplied and on the other when activated with the 12v trigger current. I have used this DPDT to reverse the current to the motor when in the 2 different positions of the relay, Thus, it has a separate up (direction) current path and a down (direction) current path. I have then added a normally closed limit switch to each of the 2 paths Up and Down that will break the current to the motor when the switch is tripped by the lift arriving to its up or down position.

So when the 12v trigger is supplied the lift moves down until the limit is reached and the current is stopped by the limit switch. Then when the 12v trigger current is removed, the relay returns to the other (reversed) position and moves the lift up until the upper limit is reached and current is broken by the second limit switch.

Next time the projector provided the 12v current we start all over again.

For a momentary 12v trigger:

I have found a relay that is DPDT that will toggle on a momentary 12v pulse. It must however also have a continuous 12v supplied by a separate source to hold the relay in its latched position until the next pulse.

Thus, either way, I think I am covered.

Scott, thanks for the help and the link to Altronics. They have the toggling relay and set me on the right direction.

Mike

Your vey welcome Mike. I think you should get your parts, put then together and get that lift moving. Sounds like your covered!

I, too, have had trouble with low output 12v triggers. B&K and Lexicon both have used them. After fooling around for years with Radio Shack reed relays and other stuff I've found that Niles offers an optocoupler, the OPT-512 (I think) that does the trick. Also, Elk offers a relay that trips at 1.2ma of output for some $25 or so.

Owning a B&K AVP-4090, I'm very familiar with the 15ma. output capacity. I used a 12v. reed relay (which has a coil current of 11ma.) to activate a 120v. relay with 10a. contacts, which in turn powers a 25a., 4-pole contactor which control 4 of the 8 circuits in my sub-panel.

I installed an RCA jack on the front panel of the sub-panel for the connection to the B&K, soldered the two smaller relays onto a piece of perf-board, soldered on the wires, put the board inside a heavy-duty plastic pouch, and put that and the contactor inside the sub-panel.

The 4 circuits are (1) the switched electronics, (2 & 3) the two amplifiers, and (4) the sub amps. The other 4 circuits are (1 & 2) lighting, (3) the unswitched electronics, and (4) the CRT projector. Total cost for the relays and parts was about $15, since I had the contactor.