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Topic: Arduino Yun 5v pin doesnt give me 5v. (Read 13838 times) previous topic - next topic

laapsaap

Jan 10, 2014, 08:03 pm Last Edit: Jan 10, 2014, 08:06 pm by laapsaap Reason: 1
Hi,

Today I opened a new yun out of the box. And i was measuring the onboard 5v/gnd pin. I tried every power supply I have and all of them supply steady 5v. But when I measure the 5v/gnd pin, its fluctuate between 4.3v and 4.5v. Is this normal?

I also try feeding power using the Vin pin, but also around no 5v from the 5v pin.
I left my other 2nd yun some where else, so I cant double check it on another one.

CrossRoads

Seems a little low. Are the supplies capable of supplying enough current? That would make the reading low.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

laapsaap

#2
Jan 10, 2014, 08:28 pm Last Edit: Jan 10, 2014, 08:39 pm by laapsaap Reason: 1
I started with 500mA then I tried using steady 1A and 2A, didnt matter much.  So is there a problem with fuse?

If I power the Yun using Vin, the 5v pin drops to 4.3v.

NewLine

I just measured mine, gives about 4.48 volt (low quality meter)

laapsaap

Thats quite low too, didnt expect that. Thought my board was faulty.

I guess I will just power things externally

sonnyyu

http://forum.arduino.cc/index.php?topic=190300.0







Quote
First of all i noticed in the schematic that there is a schottky diode placed between VIN pin and VDD, and an other between VDD and 5V pin of the board.
This could lead to a series of problems, because of voltage dropout induced by those diodes.
In particular:
1 - Voltage instability, because the voltage drop is current-depending, so it will not be stable, but could fall or raise depending on the current absorbed in the moment
2 - Diffente voltage between components: some components would receive some millivolts more or less
3 - Inaccuracy in sensors reading, because many analog sensors output a voltage that is proportional to the VCC supplied (for example the ACS715)


my 2 cents:
1. Voltage instability with temperature.
2. AR9331 no effect by Voltage instability since it power by 3.3 V.
3. Shield is power by 5.0 V which has 2 diodes and lowest  voltage.

4.48 volt  is normal but might cause some shield fail.

laapsaap

Good explanation! Thank you.

Its good to know the 5v pin isnt reliable, nothing disastrous but very annoying needing a separate  power supply and then if you use the Vin port; to regulate/protect it.

Weird design choice indeed.. 

NewLine

What does this actually mean with respect to attaching sensors and actuators to the Yun?
I guess you need to take these lower voltages into account? What would be a solution if e.g. The 4.4v would be out of spec for some sensors or actuators?

necrodiety

I'm seeing the same thing.  I only get 4.3-4.4v from my 5v pin.  It's too bad because my Uno does 5v flawlessly.  I wish it wasn't labeled 5v....


Jantje

I really think arduino needs to rethink this design.
I have 4.5V on my 5V pin. As I use a sensor working on 5V +-5% (http://www.lem.com/docs/products/ltsr%2025-np.pdf) which is not working as expected I have another possible issue to investigate  :~

My current problem is that I am making a shield with external power (isn't yun perfect for mobile apps?). As the USB connector is different and the pins behave different I require electronics beyond my knowledge to switch between Arduino boards.
So simply testing with a Uno that has 5V on its pin is ruled out as well.

So please Arduino team fix this in the next release

Best regards
Jantje
Do not PM me a question unless you are prepared to pay for consultancy.
Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -

thos37

If you're feeling adventurous you can remove the diode that's next to the VIN pin and short its two pads together.  My analog readings are much better now.

cblue

Hello,

I have same issue with my yun powered through VIN using a LM7805.

The rest of my circuit (sensors, ...) is on a breadboard. Do you recommend powering the breadboard using the clean 5V coming from LM7805 or using 5V pin of the Arduino with ~4.4V ?

Thanks,

A.

(a newbie with electronic stuff :-p)

thos37

I would use your external 5V to power at least your external sensors, since they will likely use that as a voltage reference as well. I needed to read values from external current sensors whose output is based on the 5V as reference.  So both my Yun's ADCs and my external sensors needed to have exactly the same 5VIN.


Hello,

I have same issue with my yun powered through VIN using a LM7805.

The rest of my circuit (sensors, ...) is on a breadboard. Do you recommend powering the breadboard using the clean 5V coming from LM7805 or using 5V pin of the Arduino with ~4.4V ?

Thanks,

A.

(a newbie with electronic stuff :-p)

cblue


tonysnark

Same issue here  :0 - furthermore, my YUN's digital out pins are even weaker.

I'm using USB power

Sending HIGH on Pin 13 only gives me about 2.1v (discovered the issue when it wasn't even enough to throw a 5v micro relay)


5v Pin only gives me about  4.1


3.3v Pin only gives me about 3

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