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Powering Netduino+ with 5V


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#1 Miha

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Posted 11 January 2011 - 08:24 PM

I will have to power ND+ from a 220V source. I have a small switcher 5V / 0.5A switcher available for that. Since ND+ operates through computer USB connection, I take it I could power it with that as well? Would I need to wire it to "USB power" for that to work? What could happen in case I need to plug in USB from the computer? The whole setup will use a cellular shield as well. Any problems with regards to max current (0.5A? that switcher provides)? Thanks, Miha.

#2 Jan Olof

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Posted 11 January 2011 - 09:28 PM

Miha, You can power it with +5V through the USB connector, or with 7,5V to 9V (perhaps even 12V but that could be maginal on the regulator) through the barrel connector. The pin marked +5V is on the output of the regulator and I am not sure if that would be happy if you connect 5V here. I not sure what would happen on the USB if you connect a computer at the same time (I would not do it). I have the feeling that 5V 500 mA is to little to power for your cellular shield, you must check the datasheet or tell us which you will use. AD0 to AD3 can drive 16 mA the rest 8 mA but all outputs together max 200 mA. There is a note that 5V can make problems if you use the built in pullup (I don´t see exactly what the problem is). Chris: It would be nice if there was a specification for the card regarding I/O voltages and current and also power, now you have to dig into 687 pages CPU datasheet. /Jan Olof

#3 Miha

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Posted 11 January 2011 - 09:42 PM

Jan, I ordered Cellular shield with SM5100B. The datasheet says it uses 2A in peak GSM transmission, so that pretty much answers my question...

Do you know of a way I could put a simple transformer from 220V to 12V (~2A) on board? Maybe a switcher exists with such specs... Mayber something like this only smaller (there are no dimensions, but it looks big on the picture)?

Or should I just go with the external 12VDC power supply to barrel connector? (but it's supposed to be wall-mounted thermostat...)

Regards,
Miha.

#4 Jan Olof

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Posted 11 January 2011 - 10:30 PM

The cellular seems to take its power from the VIN and it is then regulated down to 3,8 V, on the netduino+ that seems only connected to the barrel connector. The 2000 mA is peak current, average is around 350 mA when transmitting. I would look for a wall brick that gives 3A at 7,5 V, Hmm, I looked did not find any, 5V 3A is common. You can perhaps break out the connection so you don´t take the power to the cellular from the netduino, and power the netduino via the USB connector. I would be careful supplying 12V, it might be on the limit for Netduino, and the cellular shield is dimensioned for 5V, the regulator there might go up in smoke with 12V (the datasheets are really very sparese with information). Those 2A peak makes it complicated, it is really built for a battery. Anybody with a better idea ? /Jan Olof

#5 Chris Walker

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Posted 11 January 2011 - 10:35 PM

Jan: the Netduino and Netduino Plus have built-in resettable fuses that help protect the USB port against reverse voltage and overcurrent conditions. Miha: you can power the Netduino via 5V regulated power on the 5V header if you'd like. BTW, the Netduino and Netduino Plus also have circuitry which cuts off power from USB when the VIN header or power barrel are used. This allows you to use higher-amperage sources while debugging. Chris

#6 Miha

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Posted 11 January 2011 - 10:38 PM

The pin marked +5V is on the output of the regulator and I am not sure if that would be happy if you connect 5V here. I not sure what would happen on the USB if you connect a computer at the same time (I would not do it).


Jan, Chris, this 5V can be used to power LCD and other "peripherals" I suppose. What is the max current I can consume through this? The specs don't mention it.

Looking at the schematics and using some google, it looks as though it is 800mA.

#7 Chris Walker

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Posted 11 January 2011 - 10:43 PM

Hi Miha, The power regulators are rated to handle 800mA. Be aware that high amounts of current (especially when driven by high voltages on the power barrel) will cause your power regulators to warm up :) Chris

#8 Jan Olof

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Posted 11 January 2011 - 10:54 PM


Looking at the schematics and using some google, it looks as though it is 800mA.


The question is how good the regulator is cooled, if you supply with 12V you have to drop 7V
with 0,8A that makes 5,6 Watts to dissipate as heat (7,5 V supply you only have to drop 2,5V that makes only 2W as heat).

Chris:

Would a good solution be to supply +5V (a little more than 2A) on the VIN header, that would then power both Netduino+ and cellular shield one like this
Posted Image

/Jan Olof

#9 Jan Olof

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Posted 11 January 2011 - 11:55 PM

The subject have drifted, this is about powering from 12V. From the datasheet of the regulator, at a ambient temperature of 25 C and a voltage drop of 7V it can supply 400 mA with L=25 mm copper (but I am not sure of the board layout). So I am sure it can handle the Netduino at 12V, but I am sceptic about drawing 800 mA at 12V input (depending on the board layout). Max junction temp is 150 C, at 25 C ambient then it can rise another 125 C, that means that at 5,6W dissapation the therman resistance must be below 125/5,6= 22,3 C/W and that is way outside the diagram shown for the DPAK. /Jan Olof

#10 Chris Walker

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Posted 11 January 2011 - 11:57 PM

Would a good solution be to supply +5V (a little more than 2A) on the VIN header, that would then power both Netduino+ and cellular shield one like this


Technically, you could put 5V on the VIN header...but it's spec'd for 7.5V-12VDC input power. When driving higher loads, I'd recommend going with the lowest voltage.

Chris

#11 Jan Olof

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Posted 12 January 2011 - 12:48 AM

That was not a good idea, powering the Netduino through VIN! VIN is the input for the 5V regulator on the Netduino so that needs at least another 1,5V so 7,5 gives you some headroom, the schottky diode on the barrel input is specified at 1 A. Probably it would not have problem with 2A peak, but as it is a remote setup, play conservatve. I would break out the power to the GSM module and power that directly with 5V (and power the Netduino through the USB connector). /Jan Olof

#12 Miha

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Posted 12 January 2011 - 06:12 AM

I would break out the power to the GSM module and power that directly with 5V (and power the Netduino through the USB connector).


So, to summarize. Either 7.5V @ 2A or power ND via 5V, 0.5mA (USB) and provide separate for the cellular shield. It seems strange, since probably a lot of people are using the cellular shield.

What about a battery as a buffer for peaks? This stuff is supposed to just send/receive SMS messages, so I guess the current will not be as high, but one can never be sure. Say, a small battery, with simple charging circuit? The question then is:
  • How long will the battery last (how many cycles)
  • The charging circuit also complicates things a bit (don't over charge the bat, etc)

... but it seems (to me) that this would be the simplest solution of all...

#13 Jan Olof

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Posted 12 January 2011 - 09:26 AM

Miha, Take a close looka at the cellular datasheet, there might be charging circuit in it! It says optional, but if that means it is an option you can order, or if it is optional to use I don´t know. Next question is if the pins you need to connect to is available on the shield. It is the small things that makes life complicated :) . /Jan Olof

#14 Miha

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Posted 12 January 2011 - 11:22 AM

Take a close looka at the cellular datasheet, there might be charging circuit in it!


Will check that out as soon as I get it.

It is the small things that makes life complicated :) .


So true :)

#15 vojche

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Posted 08 March 2011 - 10:16 AM

Technically, you could put 5V on the VIN header...but it's spec'd for 7.5V-12VDC input power. When driving higher loads, I'd recommend going with the lowest voltage.

Chris


Can I use 12V DC (Battery) as power supply for 100 mA load?




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