Output voltages on different arduinos (5V & 3.3V)

Hey,

since days i am trying to get a GSM / GPS module to work with an arduino pro mico but without any success. I almost blamed the GSM module until i tried different arduinos. The problem was, that the module doesnt even turn on. Now i (think) i found the Problem: The 5V output is extremely different on different rduino models - in fact so different, that sometimes its so little, that it does not get recognized as 5V line. Here is my findings:

Arduino UNO 5V Out: 4,8V Leonardo: 4,2V Teensy3.2: 4,9V Pro mini: 4,0V Due: 4,8V Mega: 4,1V

I originally wanted to use the pro mini - so i played around with it for days until i had the idea to measure the voltages... (yeah... i am a total beginner...).

So my question here: is this normal!?!? So i can only use the uno, Teensy and Due (wich is way too big) to reliably power 5V modules!? I dont get it...

Al the tests were made with the same (powered) USB Hub.

Am i wrong or is this normal - so do i need some kind of stepup/down thing in every cirquit?

Any Ideas would be awesome!

Thank you so much!

Pcace

No, its not normal, something is very wrong if the 5V output isn't in the range 4.75 to 5.25 which is the expected range.

Are you overloading the output with too much load perhaps?

Are you powering each Arduino correctly?

No, all those things use an LDO for the voltage regulation. Those are normally stable and accurate to at least 0.1V. If you didn't wire something very wrong, I suspect an error in your measurements. Can you measure the overall current going in your circuit?

Hey, i am not using anything on the arduinos, but my multimeter when i measure the voltages. I have a feeling (yeah... really just a feeling) there are 3 Arduinos here (among ~10) wich output the correct rating. Those Arduinos are 2 Unos and one Due. All the other either output complete garbage or even nothing (one leonardo has 0.0V out at the 3,3V pin?!?!). But i have to say that there seems to be a slight correlation between cheap china clones wich, (as far as i can remember) are the ones doing nonsense. The three "good" ones i guess were the "expensive" ones. Is that possible? I never had trouble with them before!? (but i usually do projects like bla bla move servo there blink beep...)

For example the Leonardo: is there any "trick" getting the 3,3V to be outputted? Or is it just not working?

Cheers

Don't GSM modules take a shitload of current to operate? Link to the datasheet for your module. You're probably overwhelming the poor regulators.

I have a shitload of cheap Nano clones (hardly ever use them nowadays in favor of Wemos D1 Mini - more powerful, just as cheap, "more original" and Wifi is often a nice extra gadget). I also regularly buy the cheapest LDOs from Aliexpress. Never have I experienced anything like that. Something is wrong with your measurement.

You always have to check the current sourcing ability of a supply before putting a load on it - if the load is too great the supply will not handle it and droop or cut out.

pcace: Now i (think) i found the Problem: The 5V output is extremely different on different rduino models - in fact so different, that sometimes its so little, that it does not get recognized as 5V line. Here is my findings:

Arduino UNO 5V Out: 4,8V Leonardo: 4,2V Teensy3.2: 4,9V Pro mini: 4,0V Due: 4,8V Mega: 4,1V

All the tests were made with the same (powered) USB Hub.

Hi pcace, this (usb powered) is the reason for at least some of the discrepancy that you are seeing. The different boards have different ways of deriving their on board "+5V" from the USB supply "V_usb".

The problem arises because the boards cannot use the USB supply directly, as it would clash with the "Vin" (through onboard LDO regulator) supply if one was used. For this reason there needs to be some method of switching between the USB supply and the Vin supply, and this may involve some loss of voltage.

The UNO for example has a very nice P-channel mosfet switching arrangement which allows the board's internal +5V to be within millivolts of the external USB supply. The NANO on the other hand has a much more rudimentary schottkey diode arrangement that could introduce up to about 350mV drop between the external USB supply and +5V. Given that the USB voltage might be a little under 5.0 volts by the time it gets to your board anyway, it's not at all unusual to end up with only 4.4 volts or so with a USB powered NANO.

I'm not familiar with all the boards you quote, but I strongly suspect that it is differences like that above causing the voltage discrepancies. One solution would be to power them from a higher external Vin (7 to 12 volts on the appropriate Vin pin or jack), which will bypass the USB supply and power them from an onboard LDO regulator instead..

Hi thanks for the explanation!

Testwise i tried to power them from external 12V and -> you are right they all pretty much end up at 5V. Still strange tho...

But anyway.. i ended up using a Teensy3.1 it was (besides the mega/due) the smallest wich could provide me 3 "real" rx/tx lines...

So cheers!

Pcace

You are apparently drawing a lot of current. Only because the voltage doesn't brake down does not mean that the LDO will not burn out. You need to measure what you need and look into the datasheets.

So I checked the specs on Sparkfun's SM5100B GSM module, and its communication mode current draw is 350 mA. That is huge, and it well into the territory of needing a SMPS instead of a linear one. I accidentally ran an LCD with a 230 mA backlight from a 7805 with 12V input, and the regulator's TO-220 package got roasty-toasty warm very quickly. Whatever SMT device is on your Arduino board isn't going to have a chance of coping with that.