annunciator LED box

I am building an Annunciation box for a special project to be used in a vehicle. The signals used to trigger the LED's may be GND or 12V or 24VDC. The circuit I have come up with seems to work on paper but I have not nailed down a dimmer circuit for it. The schematic I attached is one of 24 circuits in this unit. If I can control the 12V feeding the display LED manually I'll have this thing licked . Do I need to control the voltage or the current? And hows the best way to do that so that all 24 LEDS will be dimmed the same amount. I envision that one would hold the test lamp as the adjustment is being made. Also for safety I don't want to completely turn off the LED's. Probably just dim them to half the max lumens.

Any help is appreciated.

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First question since you are working with DC to the opto coupler LED emitter why a dual LED opto coupler which I believe is designed for AC applications or if input polarity is unknown.

Ron

The reason I chose the 814 is so my input signal won't matter. Any input (i.e current flow direction) will light one or the other opto input led. All I have to do is install a jumper to the correct source to complete the circuit. Also later if I want to reconfigure one of the annunciators for a different signal input it just entails moving a jumper.

FYI...This dimmer might just do what I want? https://www.mikesflightdeck.com/led_dimmer/leds_and_dimming.html

I want it to have the capability to change the input signal by moving a jumper to change the current flow direction.

Here is a dimmer I found that may work for all 24 LEDs.

https://www.mikesflightdeck.com/led_dimmer/leds_and_dimming.html

New schematic with dimmer circuit. I was going to breadboard this next week unless there is a better simpler way.

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OK, understand why that opto coupler. Real quick before I leave work and looking at your dimmer. I see the LM7812 in there. The LM7812 has a dropout voltage of 2 volts. Meaning it would need a 14 volt minimum input to work. It would not work with a 12 volt input. What is the object of the dimming as in why?

If you note in the link with 12 volts applied they use a LM7805 so the 2 volt dropout voltage is not a problem.

Ron

The dimming is for at night so the driver or operator is not blinded. Full bright during the day will be needed. Also, most alternators put out 13.8V and I wanted the option of installing this in a 24V system although I may never do it. At the 13.8V and using a 7812 I will produce a lot less heat.

OK, I have an idea of what you are after. While the lure of working on a 12/24 volt system I would (for now) just focus on the more popular for basic automotive 12 volt systems.

You want to design and build a LED supervisory panel. When a monitored parameter has a problem a LED either extinguishes or illuminates, I would opt for illuminates.

Yes, a normal running automotive system runs at about 13.8 volts. However, higher voltages are not unusual. The problem is whan the engine isn't running. A typical battery voltage for a fully charged 12 volt battery is 12.65 volts dropping to 12.45 at 75% and about 12.24 at 50%. So anyway, sans running engine you have 12.65 volts maximum. Rather than a generic 7812 regulator with a 2 volt drop out voltage I would choose a regulator like the LM2940/LM2940C 1A Low Dropout Regulator. Some will argue what is known as "Load Dump" in automotive applications but in the interest of keeping things simple and inexpensive I would use the regulator I mentioned. Load dump is another story and interesting Google I will not delve into.

I would not bother with a dual emitter LED emitter opto coupler as I see no need for it? You have ground and 12 volts in an automotive system and I can see no need, however, other members or yourself may want to point out why it would be practical? Just means I don't see the need and not that there is a need.

Moving along to the dimming aspects. Now my truck is smarter than me. I would go with PWM (Pulse Width Modulation) for dimming using a circuit along these lines. That scheme allows the user to set the LED brilliance for day or night or really anything pleasing to their view. The adjustable 50KΩ resistor may be replaced by a LDR (Light Dependent Resistor) or photocell on the dash to automatically control dimming. My truck seems to have a handle on it anyway.

The above is just a few ideas of how I might go about it. I tried to support my thinking as to the why. It would be cool if others chimed in with some thoughts.

Ron

I like it... If I wanted to have just 2 LED levels and not make it variable, would this work?

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Yeah, something like that would work for a simple solution. Adding resistance to the series resistance with the LED will limit the current and subsequently the brightness (intensity) of the LED. This is one of those projects that can be as simple or complex as you want it to be. You can eliminate or add features depending on your bottom line. Since I have not seen the data sheet for your specific choice of LED I can't comment on the resistance values but yes, that would work.

Ron