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Have 3,3V need 15V

Stuefi

Aug 4, 2022
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Hello.

I need your help. I'm controlling some LEDs with my Arduino. That means that I get an output of 3,3V. The LEDs I want to power require 15V. So how can I solve this?

My idea was that I just use a relai (for example the SRD-05VDC-SL-C). Then the 15V would have to come from an external transformer. What do you think? Is that a good idea or is there any smarter and cheaper way?

Lg Stüfi
 

kellys_eye

Jun 25, 2010
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What method are you using to control the LEDs? Directly? Simple on-off? Variable brightness?

Most users drive them via transistors of MOSFETs - show us a schematic or block diagram.
 

Stuefi

Aug 4, 2022
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upload_2022-8-4_18-42-59.png
That's the plan. Just ignore the buttons. I want to swith the LEDs on and off. In my test i used normal LEDs (like in the picture) but in the end product there should be some other LEDs that use 15V.
 

Alec_t

Jul 7, 2015
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You can use a level-shifter as a driver for a LED, based on this principle :-
LED-driver.jpg
The component types/values will depend on how much current the 'LED' draws. Rx represents the current-limiting resistor in series with the 'LED' (which is presumably a LED module rather than a single LED, if it is rated "15V"). Note that this arrangement needs a logic high from the Arduino to turn the LED on.
 

Stuefi

Aug 4, 2022
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I don't think that it's a LED module because it looks like a normal LED;). But in the instruction it says "operating voltage: 14-16V".
Can I buy these level-shifters some where or do I have to build them? The scheme above is just a test. At the end I will need many more LEDs in my project. So building the level-shifters by myself isn't really an option.
 

Alec_t

Jul 7, 2015
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it looks like a normal LED
A single 'normal LED ' has a forward voltage of about 2V if it is red/green/yellow or about 3V if it is blue/white. Anything rated higher means it is either a series string of LEDs or else a single LED combined with a series current-limiting resistor.
I have never searched for off-the-shelf level-shifters, so don't know if they exist.
Can you post a link to the '15V LEDs' you intend using?
 

Martaine2005

May 12, 2015
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The are obviously single LEDs with with a current limiting resistor to 10mA. The diode may well be to rectify the AC in this case.


Martin
 

Stuefi

Aug 4, 2022
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Ok. What should I do now? Should I now use some relais and power the LEDs with the electricity from the transformer? Or is there a way to change a 3,3V or 5V DC power to 14-16V AC?
 

Martaine2005

May 12, 2015
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Reading this thread back, you want these signal lights to run off an Arduino but they are 14-16V AC?.
Personally, I would see if I could access the series resistors and change them for use with 3.3V or 5V.


Martin
 

Alec_t

Jul 7, 2015
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The light control module 5221 has an input clearly marked as AC (~). This AC supplies the diode, the cathode of which is connected to the lights. Hence the lights receive half-wave rectified AC, i.e unsmoothed DC. This DC could be used as the supply for the level-shifter circuits. If the lights have to be indivdually controlled then you will need one level-shifter (or relay) per light.
The cost of a level-shifter is almost certainly less than that of a relay with back-emf protection. Either solution will mean some construction on your part.
 

Stuefi

Aug 4, 2022
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I have now calculated the resistor I would need. So what will happen if I change the resistor and power the LED directly from the Arduino. That would mean that the LED receives a smoothed DC power. Would that damage the LED?
 

Martaine2005

May 12, 2015
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That would be the easiest and cheapest way to do it. No point in buck/boost circuits, relays, more wiring etc.
The LEDs will prefer DC and won’t tend to flicker due to half rectified unsmoothed DC. And be perfectly happy being controlled by the Arduino.


Martin
 

Stuefi

Aug 4, 2022
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upload_2022-8-5_17-57-33.jpeg
If I do it like that I have just noticed a nother problem:

Whan you look at the picture you will notice that the black wire is the + pole. (because the diode only lets power into the signal)
That means that the coloured wires have to be GND. But I can only sat the pinns on the Arduino to HIGH (3,3V) or LOW (nothing). How should I turn the LEDs individually on and of? Or is ther a way to set every pinn to GND how I need it?
 

Martaine2005

May 12, 2015
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FPBEG4NFK8FVU92.png
 

Stuefi

Aug 4, 2022
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upload_2022-8-5_18-43-50.png
If I want that the red LED shines I have to put 3.3V on the + and GND on the -. But I don't think it's possible to make the pinns on the Arduino GND. Also if the diode wouldn't exist. The diode just saves the LEDs not to be used in the fals direction.
 
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