Design glitches: Arduino Nano supply voltage

DIY STUFF
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(thought I’d collect my nano supply notes in one place to make it easier to link to)

A common design glitch in circuits that use an Arduino Nano is to connect regulated 5 V to the VIN pin instead of the +5V pin. This results in the Arduino running at a lower internal supply voltage, often 4 V or below, which may be a problem if the design depends on analog inputs or digital output levels. Voltages below 4.5 V are also out of spec for the 16 MHz clock used by the Nano.

Details below, but TL;DR if you have regulated 5 V, connect it to the +5V pin, not VIN.

To see why this happens, here’s the general layout for the onboard power supply on an Arduino Nano:

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The +5V input (pin 27) is connected directly to the main internal 5 V VCC rail on the Arduino. If you provide power via VIN or USB, this is an output.

The VIN input (pin 30) is connected to a voltage regulator, which brings the input down to a regulated 5 V. This circuit causes a voltage drop as the current passes through the regulator’s internal circuitry. This drop is typically between 0.8-2.0 V, depending on what Nano you’re using, so if you feed in 5 V here, the “5V” rail (internal and 5V pin) will be at between 3.0 and 4.2 V:

  • The Arduino Nano 3.2 uses an LM1117 low dropout linear regulator, which has a 1.2 V dropout, and internal rail will be ~3.8 V.
    • Cheap clones often use an AMS1117 instead, which has similar specs.
  • The Arduino Nano Every uses a fancy $3 MPM3610 step-down converter which can handle higher input voltages (up to 21 V) and more power, and do that more efficiently. It has a dropout equivalent of ~15% of the input voltage, so internal rail will be ~4.25 V.
  • The older Arduino Nano 3.0 uses a UA78M05 linear regulator with a 2.0 V dropout. Internal rail will be ~3.0 V.

You can also power the Nano via USB. In that case, the power goes via a (Schottky) diode, with a voltage drop of ~0.3 V, so the main 5V rail will see ~4.7 V.

(conversely, if you need the rail to be exactly 5.0 V, you need to either feed regulated 5.0 V to the +5V pin, or feed 5.0 V plus at least the given voltage drop plus a bit of margin to VIN.)

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Indeed on the Big Button and the Sequencer the regulated current is connected in Vin.
I don’t think I would take them apart to change because it still works well like that, but it’s very good to know for my next Arduino-based constructions
thank you

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Not sure what you mean by that and I don’t see the answer in the datasheet. I guess I’m asking what you mean by “dropout”.

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Well, dropout (Vdo) equivalent, if you want to be picky :slight_smile:. Vout is Vin*Dmax where Dmax is typically 85% (yes, it took me a while to spot that too). I translated that to equivalent Vdo to keep things consistent.

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Ah, I see — this part doesn’t have a fixed output voltage, you select it with an external voltage divider, and that can be up to 85% of the input voltage. Dmax is the maximum duty cycle.

I was confused because I was thinking of fixed voltage regulators.

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Thank you good Sir, for pointing out that the VIN and +5V pin serve a different purpose. I had an Arduino Nano resetting erratically, and I discovered that I had used the wrong pin to supply 5V to it.

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So, I’ve noticed the Big Button doesn’t have enough voltage out to trigger pretty much any drum module I have other than MI Braids. Could changing to 5v make a difference in this case? I was going to attempt to add some op amps to boost the signal., but this would be easier. Probably wishful thinkin”.

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What voltage do you have now? Putting the output of the regulator onto the +5V pin instead of the VIN pin should give you ~5V gates which ought to trigger any well designed module. “Ought”. “Well designed”.

But if not, boosting an anemic gate shouldn’t be too hard to do. A transistor and a couple resistors may be all you need.

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I did also do this mistake on my stripboard for a little arduino synth (basically a clone of a ginkosynthese seeds) And I am wondering now if that may be the issue with my tuning issues… maybe it’s something different, but I could imagine that having a different reference voltage could be a problem here…

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Happen to have any plans or a link for building that?

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It’s basically this for the output

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Just the things on pin D11. left wire goes to the output jack.
The code is in the First link. From this you can make your inputs and potentiometers

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I got part of that. Could you elaborate a bit on the build? Not sure what I’m seeing above. Where do pots and jacks go? Did you find a layout for this somewhere? It’s pretty cool.