Hi everyone! I would like to test and program the following RGB rotary encoder with Arduino. (this circuit is an already finished PCB) Is it somehow possible with that 9.5 V power supply? If not possible, how else could I test it?
Welcome!
Nice start with the schematic, but there’s not enough detail to be helpful.
Add part numbers for the chips—I have no clue what you’re using at this point.
If the component in the top left is a switch, you’ll end up frying your LEDs. You need to add resistors in each string to limit the current.
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The circuit I drew is an already finished PCB and I would like to test it. Components top and bottom are connectors. I have now developed the following circuit to test it (I added MOSFETS and resistors). Would this work?
No, it will fry your LEDs as you don't have resistors in series with each string of 3 LEDs.
I'm puzzled that you had a PCB made but initially posted a hand drawn schematic, how did you create a PCB without a schematic?
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Thank you for the answer. The board wasn't developed by me, but by an electronic device manufacturer. I'm just trying to test it
This does not seem a high enough voltage.
The green and blue LEDs in RGB LEDs normally have a forward voltage of 3~3.5V. When 3 of these are connected in series, the total forward voltage will be at least 9V, and could be as high as 10.5V.
As mentioned by others, you need some current limiting resistors, and these will also need to drop some voltage. If they can only drop a small voltage, they may not be able to limit the current enough, and this could damage the LEDs.
So I would recommend using a 12V power supply and choosing your current limiting resistor values appropriately. Remember that the red LEDs will have a much lower forward voltage and so need a higher value resistor.
I would also recommend that you learn how to calculate those resistor values and post your answers here so the forum can check you got them correct. Re-post your schematic showing where you would connect the resistors.
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Thank you for your answer! Ufr = 2V, Ufgb = 2.8V. The problem is, this circuit is an already finished PCB. How else could I limit the current and test it?
Not enough resistors. You need to add current limiting resistors for the LEDs.
What current do you want to flow through the LEDs? Let's say that is 10mA.
For the green and blue LEDs, the current limiting resistor should be
(9.5-3*2.8)/0.010 = 110 Ohms
For the red LEDs,
(9.5-3*2)/0.010 = 350 Ohms
Choose resistor values close to but higher than the above.
You have to cut the tracks and insert the resistors, there's no way round this, the board design is wrong.
Perry is correct, there is a flaw in the design.
Ideally, each group of 3 LEDs in series should have it's own current limiting resistor. But the tracks on your PCB have pairs of LED groups in parallel, which means you cannot connect a resistor for each group, only a single resistor for each pair of groups.
If the LEDs used are all from the same batch of LEDs manufactured in the same factory, they should all have very similar characteristics and share current almost perfectly equally between the parallel pairs of led groups.
If they are not from the same batch from the same factory, they may have different characteristics and may not share the current equally between the groups. Whichever group has the lower forward voltage will take more of the current and may fail or age faster.
Hopefully the PCB manufacturer has used LEDs from the same batch and factory and the LEDs will have a long enough life. If not, return them for a refund and use a better manufacturer next time.
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I beg to differ, my brother had some fancy lights for his hall, the LEDs were wired in series / parallel pairs very similar to what the OP has. All failed over time. I made new LED boards for him with current balancing resistors in each string of LEDs, so far none has failed.
I think the failure mechanism is that as LEDs heat up they conduct more and so their Vf drops. Whichever of the 2 strings in a parallel pair of strings heats the most has the biggest drop in Vf so gets a bit more current, leading to them getting hotter and Vf falling some more, until the current is too much and an LED fails.
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RGB Rotary Encoder is just for an exibition. The LEDs will only be on for a few minutes It should looks like this: https://www.youtube.com/watch?v=XwJAsMYqPkA. So, if I would connect a single resistor for each pair of groups, would it be fine?
If you use a resistor that will keep the current for each LED below its maximum rated current then you should be OK, for example:
You have 2 strings in parallel, check the maximum forward current for the LEDs in each string. Suppose the maximum is 20mA, then if your resistor limits the current to 20mA, meaning that each string gets about 10mA, then no LED will ever get more than 20mA, so should be OK. If it really is only for a short time then you will be OK. Obviously my brother's lights were on for hours at a time.
I love the way those LEDs are used in the video!
Edit, for indicator LEDs like in the video you probably don't need anything like the rated current to get enough brightness. Experiment. If you don't have a selection of resistors then buy a kit of assorted resistors.
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Thank you both, you really helped me
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With the possible exception of the encoder on the right, I think those other effects could be achieved mechanically using fixed white backlights and colour filters and a mask that moves mechanically with the encoder.
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