What is the purpose of the zero-Ohm resistor R25 on the Arduino MKR IoT Carrier Rev2 board (firm schematics see below)? If it's needed to adjust the LED brightness, it could be adjusted using resistor R3. There are no wires underneath resistor R25 on the PCB, so there's plenty of space (see PCB below). Any suggestions?
usually the only purpose of a zero ohm resisitor is to bridge tracks that cant otherwise conveniently be routed.
Possibly "remove this to disable LED".
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Do I need to be the official Arduino designer of that board in order for you to accept my answer?
I specifically attached a drawing of the PCB to show that the tracks do not pass under the R25 resistor (there is a lot of space).
I'm also inclined to agree, but to turn off the LED, you can also desolder the resistor R3. Incidentally, this same shield IoT Carrier also has two more zero-Ohm resistors in the same configuration for the other two LEDs, but they're used for mode indication, so it's unlikely they were intended to be turned off to save power..
I don't feel like arguing, and honestly I can't see why it matters.
Apparently so.
May I offer another explanation? The board design may have had a trace under the resistor at one time. A modification may have eliminated or moved the trace. To change to BOM and the program of the pick and place machine would cost more than the cost of the resistor, so it was just left in the build.
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The marketing department found that the board looked too bare and wanted to bulk up the component count without incurring significant additional cost.
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It could also simply be some kind of screw-up where an extra resistor was added.
I've seen something different once where there were two pull-ups in parallel where only one was needed. One could be deleted but maybe no one noticed it... Or maybe it wasn't worth changing the documentation and assembly revision just to save the cost of a resistor...
This is a different situation but where I work we make 2 versions of a board. One version runs from 12V and it has a voltage regulator. In the 5V version, the voltage regulator circuitry is omitted and bypassed with a zero-Ohm resistor.
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I used to use zero ohm resisters extensively when I was in industry. In this case it looks to me like It was being used as a simple way of increasing the the resistance of the seriese resistor by removing it and replacing it with an extra series resistor.
Sure you could just remove R3 and replace it with another value, but by replacing the zero ohm link you always have that fixed amount of current defined by R3. You could also insert a resistor to monitor the current for other purposes.
Components on the underside of the board are costly, and professional engineers are very risk averse species.
We used to wind up the purchasing department by specifying 1% zero ohm links. ( joke think about it )
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Thanks for the interesting suggestions.
The board design may have had a trace under the resistor at one time. A modification may have eliminated or moved the trace. To change to BOM and the program of the pick and place machine would cost more than the cost of the resistor, so it was just left in the build.
An original idea, but... There are two more similar nodes on the same MKR IoT Carrier 2 board (see below). It's hard to guess - three tracks were previously routed under the three resistors.
Components on the underside of the board are costly, and professional engineers are very risk averse species.
This is an interesting option, but the MKR IoT Carrier 2 board has soldered components on both sides of the PCB.
You could also insert a resistor to monitor the current for other purposes.
This is a good assumption and would be useful in another circuit, but not in our case. Monitoring the current through an LED intended for a standard 5V power supply indication is pointless.
Assuming the zero-Ohm resistors function as jumpers (turning the LEDs on and off), the developer of the MKR IoT Carrier 2 board should have indicated this capability in the datasheet. However, there's no such text in the datasheet or on the schematic. Perhaps the author, Francesca Cenna (see below) from Arduino Team, could clarify the logic?
The numbering of the 0 ohm resistors is strange, out of the normal series, as if it was a "late" design decision.
As in your other topics regarding zero ohm resistors, it's highly unlikely that the board designer will respond to your request.
I was just trying to think of all the possible uses of that configuration.
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You are welcome