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Safe Way to power netduino with 5v Regulated Supply


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#1 Caconway

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Posted 07 February 2013 - 01:34 AM

Is there a safe way to power a netduino plus with a 5v regulated supply that will not cause problems when a usb cable is connected?



#2 Mario Vernari

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Posted 07 February 2013 - 04:15 AM

Do you mean powering the board from the +5V pin of the header and from the USB at same time?


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#3 Caconway

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Posted 07 February 2013 - 06:12 AM

I honestly don't know. I saw somewhere that you can power it with 7.5 to 9v on the vin pin but what I'm wanting to do is power it from a 5v regulated supply but be able to safely connect a USB cable. Is it safe to power it from the 5v pin and still connect a USB cable without using the vin pin? Or how would I go about doing this? By the way this is for netduino plus 2

#4 NooM

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Posted 07 February 2013 - 07:05 AM

first: it doesent matter if its 5 or 9 volt, when you would actually connect that to usb your usb port would be damaged.

 

than: iam very very sure the netduino does have a protection for that, so that you can power it with a 7.5 to 9v power supply and still have it connected to usb



#5 Mario Vernari

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Posted 07 February 2013 - 09:41 AM

So...

 

Barrel plug / Vin.

They are exactly the same rail: you can apply as low as +6..7V up to +10..12V. Higher voltages may be applied, but there's an issue related to the protection circuit, so consider +12V as the upper bound. Below the lower threshold, the protection circuit will consider the USB power as primary.

Let's say that between +5 and the lower threshold, the power is supplied in a mixture of ways. Since there's no a clear ripartition of the currents in the supply stage, I would discourage to apply voltages falling in this interval.

This rail has a protection diode which prevents damage when the power is applied inverted by mistake.

 

USB power.

Any USB host supplies +5V (0.5 A max) to the connected device. As long the above (barrel/Vin) rail is missing, the entire circuit leverages on the USB power.

 

+5V header.

The "old" Netduinoes expose the +5V rail straight to the header, thus you could power your board by avoiding both the Vin and the USB. However, this voltage must be exactly +5V, well stabilized. That's because the on-board +5V regulator provided by the Netduino is actually bypassed.

The new Netduinoes "2" have a mosfet for switching the +5V header on/off. I may explain the details behind my consideration, but I would discourage to power the Netduino (Plus) 2 uniquely from the +5V header. It works, but it stresses a lot the mosfet.

 

+3.3 header.

In brief: never provide your own +3.3V external supply to the +3.3V header pin.

 

NOTE: the above description is just a *SIMPLE* list of what you may and what you shoud not do. However, there are many (complex) implications involved. I believe they should dig only for advanced users.

 

Hope it helps.

Cheers


Biggest fault of Netduino? It runs by electricity.

#6 Zbyszek

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Posted 10 February 2013 - 06:22 PM

Hello, let me re-phrase this question. My Netduino Plus 2 can be powered by:

1)  a PC via USB cable or

2)  a stand-alone 7.5-9VDC power supply.

Can both cables (USB and 7.5-9VDC) stay connected to my Netuduino Plus 2 card at the same time?

Regards,

Zbyszek



#7 Paul Newton

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Posted 10 February 2013 - 07:28 PM

Yes, you can connect a USB cable at the same time as supplying power into the Vin/barrel input.

There is a transistor that disconnects the USB's 5V line when Vin is available.

Paul



#8 Zbyszek

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Posted 10 February 2013 - 08:52 PM

Yes, you can connect a USB cable at the same time as supplying power into the Vin/barrel input.

There is a transistor that disconnects the USB's 5V line when Vin is available.

Paul

 

Thank you.

Zbyszek



#9 robbypet

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Posted 14 February 2013 - 03:29 PM

hello,i have a problem with external power.

My project include: netduino plus2, 2 "probe 1-wire" DS18B20, 2 relay with pilot (transistor bc337-25 and coil 5V).

the software to manage the probes and relays is OK of course.

i have connect netduino only with usb power.

The problem is:

when i use the pin +5V and gnd on netduino board to feeding the circuit (probes and relays) is all ok,

but if i connect the same circuit to external power  (and so on netduino i have only 3 digital pin to use) i have not results (the temperature of probes is 0 and the relays don't click)

the external power is a pwer pack 5V 0,5A



#10 NooM

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Posted 14 February 2013 - 04:11 PM

connected gnd together?



#11 Paul Newton

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Posted 14 February 2013 - 09:21 PM

Hi Robbypet,

 

Welcome to the forums!.

 

Can you post a circuit diagram of what you have wired up. The problem will probably be obvious then.

 

Paul



#12 robbypet

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Posted 16 February 2013 - 02:03 PM

hi Paul,

netduino is connect with usb in both case

 

https://www.dropbox.... wire_ralay.pdf



#13 Paul Newton

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Posted 17 February 2013 - 09:04 AM

Try joining the ground of the Netduino to the extetnal power supply's ground.

In simple terms, without it the signals don't have a reference for what is a high or a low signal.

Paul



#14 robbypet

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Posted 17 February 2013 - 04:19 PM

ok, it is that.

Thanks paul

My next step is a web interface.

see you soon






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