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SSR or other control component

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RainbowVideo

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I have a multimedia device with an external port that has 8 outputs. These outputs can be programmed to trigger (+3.3vdc) at any time during the presentation or in response to 'buttons' on a touchscreen. My intent is to use these outputs to trigger small lighting units. I need something on the order of an SSR to control each individual light. The lights operate at 12vdc and although they are LEDs, they are non-polarized.

I have 56 of these, so economy is a factor. I tried an SSR with an AC output (because I couldn't find a cheap one with a DC output) and it would turn the light on, but not off.

I next tried a ULN2803A which responded to the trigger voltage but would only illuminate the fixture only slightly.

I'm stumped. Any ideas?
 
An important parameter you left out is the maximum current you expect a single load (LED lighting unit) to require and the maximum number of them you intend to control with a single "trigger". The voltage (+12 volts), alone, is not sufficient to choose a control scheme.
 
It's a strange led that is not polarity dependant. The triac ssr won't turn of because the current never goes thru 0. The triac needs this to turn off.

The turn on voltage for the 2803 is pretty marginal with 3.3 volts. How much current does the led draw?
 
Sorry about leaving the current out. each unit is rated at 120mA. Normally I would be controlling a single unit with each trigger, but might want to control 2 units on a single trigger if possible. Re: The polarity issue, obviously there is some sort of circuit inside the light that makes it non polar. You can see the unit I'm using at **broken link removed**

On the trigger voltage. I had the same question but was assured that 3.3vdc would be okay. Under load the 3.3vdc looks more like 2.5. I don't know enough about this stuff, is is possible that if the trigger voltage is too low the unit would only illuminate slightly?
 
Cool,
Seems like it should work. Just to make sure - Pin 9 on the 2803 goes to ground on the 12 volt supply and the 3.3 volt supply.
Pin 1 is an input and pin 18 goes to one lead of the LED. The other lead on the LED goes to +12.
If that is how it is you can test the 2803 by disconnecting the input wire, then attach a wire that you can touch to the + of the 3.3 volt supply. The lamp should turn on. If not touch it to +12.
 
Not quite. Just the grounds of the 2 power supplies need to be tied together. I'm not sure where the ground for your multimedia device is. It may be one wire on a plug or maybe it has terminals to hook up to.
 
just want to be sure this is what you are saying - schematic attached. (and by the way, many thanks!)
View attachment 67604

Except you have to cut the wire connected to pin 10 and leave pin 10 open circuit (restating that just the grounds of the 2 power supplies need to be tied together, as ronv posted). If you still have a problem, check the trigger voltage when all is connected. The trigger voltage needs to be at least 2.4 volts (worst case) to fully activate one load, 2.7 volts (worst case) to fully activate two loads, the load voltage will be more like 11 volts, not 12 volts, since the ULN device will drop some of the voltage.
 
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THANK YOU!!! Tryed it and it works just as I had hoped. Now I need to be about the business of putting together 6 more. I really appreciate that there are knowledgeable people willing to share their expertise.
 
One last question. When the media device powers up, all triggers go to +3.3. That means all 8 outputs are in the 'on' state. That creates an aggregate load of 960mA and if I have to add more than one light to a trigger, it could go higher. Not a problem for the power supply, but is that too much for the chip. I looked at the specs and it seems to say 500mA per output. If that's the case, I'm okay. How do you read it? And once again, many many thanks.
 
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