Powering Neopixels - works with Micro, not with Pro mini 5v 16Mhz

Hi all ! I'm asking this question here because it's killing me not knowing if it's me, or something with the arduino specs that I'm not seeing. I'm not an electronics expert whatsoever, but love knowing why things work

Sorry if it's not the right topic

I'm doing a project and need to power a Neopixel strip (with 51 neopixels) with 3xAA (4.5v) batteries.

After all the wiring complete, if using a Arduino Micro (hard to find these days online to buy) the strip works perfectly fine and all the pixels are lit .

If using the Pro mini, it only lights 3 or 4, or sometimes more, but never the complete strip and does not performs the code when powered using the AA batteries. If powered by the USB port (using a FTDI 5v) it works perfectly... My question is why ? Is it some kind of bypass ?

Both arduinos are powered - by the batteries - using the VIN (or RAW) input .

Measuring the voltage at the output for the Neopixels strip (5v pin), with the Micro, I only get around 2v . What's is happening ? Is the Arduino damaged ?

Thank you and sorry if this question is dumb, but I need to find out why

PS: Is the Arduino Micro retired ? Is hard to find online to buy.. Is there a good alternative ? Thank you

I think the problem is you're trying to run a 5v board at 4.5v.

It'll probably work OK if you connect 4.5V to the Vcc input (disclaimer - I've done this OK with Nano's but not Pro Mini's)

The RAW connection goes through a voltage regulator which won't work properly if the voltage is already on the low side.

Looking at their schematics, the Pro-Mini has a very weak 5V regulator; it's an MIC5205 good for only 150mA maximum output current. The Micro uses an NCP1117-5 which is rated up to 1A.

Neopixels take a lot of current; a full strip of 51 is going to need more power than either reg is going to be happy supplying. If only one of R, G or B LEDs is on at, say, 20mA per LED, that alone is more than 1-amp. TBH, even a USB port shouldn't be tasked with powering this as they too are current limited.

You need a ballsier power supply setup. A few AA cells aren't going to meet the strip's power requirements (at least for long...)

thank you all for the answers.

I'm going to deep a bit more into this - try a few things more to try to understand the problem with the Micro !Probably it has something to do with the amps .

thank you all !

Blackfin:
Looking at their schematics, the Pro-Mini has a very weak 5V regulator; it's an MIC5205 good for only 150mA maximum output current. The Micro uses an NCP1117-5 which is rated up to 1A.

But neither Micro or Pro Mini is using the regulator to provide for more than the processor itself in this case. It is not the current capability, but the drop-out characteristics.

The clear blunder is not comprehending what the "Vin" or "RAW" terminal is. It is an ornament provided in the very beginning of the Arduino project when "9V" power packs were common and this was a practical way to power a lone Arduino board for initial demonstration purposes. And even then it was limited because an unloaded 9 V transformer-rectifier-capacitor supply would generally provide over 12 V which the regulator could barely handle.

If powering from batteries, as long as the battery pack cannot exceed 5.5 V, this must be connected to the 5 V pin.

Nowadays, 5 V regulated switchmode packs are arguably the most readily available in the form of "Phone chargers" and switchmode "buck" regulators are cheap on eBay so these can be fed into the USB connector or 5 V pin to provide adequate power for all applications. Unfortunately, many tutorials or "instructables" are outdated or misleading and have not been updated to reflect the contemporary situation.

The "Vin" or "RAW" terminal is essentially a legacy part, some "clones" and more sophisticated Arduinos incorporate an actually functional switchmode regulator but it should simply be ignored on the older designs. :grinning:

Certainly on pro mini's with that lousy rice-grain sized regulator, Vin/RAW is almost never useful. On boards with a 1117-series reg, it's often usable as long as the current is kept low.

Connect the batteries directly to the 5v pin and you'll have a much better chance of making it work.