Led wiring | MobiFlight | Page 1

acoustic frigate Jun 8, 2025, 7:07 PM

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Hey, I am planning to wire all the Annunciation for my 737 FWD Overhead, each Annunciation is 2 orange Leds connected in parallel (2V 20 mA). In total there is Obvs more Then 40 Leds that will be running, and i might need to use 2 Arduino Megas. My question is what resistor do i need, can i use 1 Arduino with this much mA running, is it possible for someone to make a wiring diagram, what power supply do i need. I am very new to these LEDS shiet

swift dome Jun 8, 2025, 7:09 PM

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With that many LEDs you may want to consider led driver chips

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See these pages

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https://docs.mobiflight.com/devices/output-shift-register/

Output shift registers

How to use output shift registers with MobiFlight.

twin flume Jun 8, 2025, 7:16 PM

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A regular shift register will need installing resistors in each led. A 220 - 330 ohm resistor should be good. However, there is a better alternative: using a led driver like the DM13A only requires one resistor to set the overall current per segment.

static knoll Jun 9, 2025, 3:10 PM

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acoustic frigate Hey, I am planning to wire all the Annunciation for my 737 FWD Overhead, each A...

If not using a LED driver, best is to use one resistor for one LED. Better not to connect two LED's in parallel and using just one resistor. Even if the LED type and color is the same, the forward voltage might be slightly different. When starting with this, most likely you will not see this, but over the time the brighter LED gets brighter and the darker one gets darker.

twin flume Jun 9, 2025, 3:28 PM

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static knoll If not using a LED driver, best is to use one resistor for one LED. Better not t...

A question popped up in my mind. Using a DM13A led driver, is it OK to wire two leds in parallel there? I would guess the same issue you mentioned would happen.
Wiring in series would be the preferred way (I guess), in which case, a higher supply voltage would probably be required.

static knoll Jun 9, 2025, 3:30 PM

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twin flume A question popped up in my mind. Using a DM13A led driver, is it OK to wire two ...

Yes, exactly. In series and not parallel!

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Maybe an additional small hint. With a LED driver the current for all 8 outputs is defined via one resistor. If you want to adjust the brightness of LED's which are connected to one Output, connect a resistor in parallel to the LED's. In series the driver tries to keep the current constant. This does also work for a single Led if you connect the resistor only to this LED in parallel. 😉

proud dome Jun 9, 2025, 7:47 PM

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I designed my own PCB to drive up to 96 LED with one Arduino Nano with the TPIC6B595DWR chip. Works perfectly, every LED needs its own resistor though (which is the case on my OEM panel led switches)