Dual power supply for Arduino and La Fonera

Hello,

I am creating a device that uses both an Arduino Diecimila and a La Fonera (a type of wireless router). I have connected them via serial and can control the Arduino over the internet via wi-fi. It's pretty cool ;D

Now I am trying to find the best way to power both of the devices from a single wall wart. I don't want to have two power adapters for a single project box!

Can anyone direct me to the best approach? Here are the details:

  • The Arduino requires a 9-12v, 250mA+ adapter.
  • The Fonera can be provided power through a 5v input or a 3.3v input. I have already tested and found that the Arduino's 5v and 3.3v outputs cannot support the Fonera's power requirements. According to other Fonera users, the router requires up to 800ma at the 5v input or ~700 ma at the 3.3v input.
  • My wall wart provides 650mA at 9v.

Thanks in advance, hope this is understandable! :P

Hi !

Maybe you can considerer splitting a 12V DC input in 2, the first directly connected to the Arduino, the second to the router using a 5VDC power regulator...

There's certainly an easier way, but I can't think of any.

First of all, it sounds like you need a wall wart that is capable of delivering more current if your specs about your Fonera are right.

Given that the Fonera requires a 5V or 3.3V power source that can deliver more current than the Arduino's regulator can provide, your only options would be to

A) Use two separate power supplies

or

B) Send the wall wart's power to both your Arduino and an external switching regulator that can provide the power needed for your Fonera at the proper voltage. This switching regulator would be inside your device, so from the outside you'd see a device with a single wall wart.

A possible third option would be to get a 5 V wall wart that can power your Fonera and connect its output directly to your Arduino's Vcc line (i.e. bypass the Arduino's onboard voltage regulator). I don't know the Arduino well enough to know exactly how you would do this or if this would have any negative side effects. Furthermore, I'm not familiar enough with wall warts to know if their outputs are clean enough to be used as regulated logic voltage. Maybe someone else can verify if this option would work.

  • Ben

Hi, and thank you both for the quick responses.

I was hoping I could drive the Arduino from the Fonera or vice-versa, but these solutions seem too complicated for me to pull off-- I’m no electrical engineer :’(

I know I can’t power the Fonera from the Arduino’s 3.3v because that is regulated by the FTDI USB-serial converter and only provides 50mA. The 5v output is not enough current either. Similarly, the Fonera cannot provide a high enough voltage to run the Arduino.

Thank you both for your help, even though it looks like I’ll have to make do with two wall warts.

In return, I’d be happy to tell you about how I can control my Arduino over the internet, if either of you are interested. It’s not completely finished, and I’m planning on writing it up for the Arduino and Fonera forums later, but I have the proof-of-concept-- this power issue is the final hurdle…

I've run the Arduino with 5V connected to the Vcc pin with no problem. Ive used several 5V wall warts, including cheep cell phone chargers, and even 5V "switchers" (Mintyboost & home made). (I expect they could have even more ripple than a wall wart.)

If the 5V wall wart is big enough to supply the router and the Arduino, (800(?) + ~200 or 1A), it would be the simplest way to go.

Still I hesitate to recommend this, since I don't know what kind of wall wart you will end up with, and you are not me. Let me just say that I would do it that way.

FWIMBW, I'm surprised the figures on the router show that it draws less current at 3.3V than it does at 5V. But 1A ought to cover it.

In any case, do not try to run your router (3 or 5V) from the Arduino.

Using a switching regulator isn't all that complicated, and maybe it would be a good way for you to get started dabbling in electronics...

@bens: Er, for the record, I already tried running the router from the Arduino :-/ I hope nothing is broken...

@BroHogan: I know that SparkFun sells a 5v, 1A wall wart for ~$6: http://www.sparkfun.com/commerce/product_info.php?products_id=8269

Should I plug it into the Arduino and then connect the Fonera to the Arduino's 5v and gnd pins? Or should I split the adapter's output and power the Fonera and Arduino separately (I think this is the better way)?

I once powered my Arduino using a 1A power supply (but 9v not 5v), and the voltage regulator on the Arduino board got dreadfully hot and began to smell like it would combust any second.

As for the Fonera power consumption figures, they are from two separate forum threads. Take them with a grain of salt.

If you want to do this, you shoud split the power output, connect it the +5V and GND pins on the Arduino side, and to the power plug on the router's side.

What you're saying about the 9V/1A power supply is strange. My Decimilia is almost always connected to a 12V/1A supply, the power reg heatens a bit, but is never too hot after hours of running. "1A" means the supply can provide at max 1A, not that it's forcing 1amp into the circuit. Have you tried to measure the power with a multimeter to check that it really provided only 9V ? I recently found out that my old 12V AC>DC converter gave in fact more than 20V... Which is probably not very good for the regulator.

Oh, I remember why the Fonera draws less current at 3.3v versus 5v:

For whatever (stupid) reason, the Fonera's official DC input jack requires 5v. It comes with a 5v, 2A wall wart. As soon as the voltage comes through the jack, it is immediately run through a 3.3v voltage regulator, which (presumably) sucks up more current and (undeniably) gives off heat waves of hellish proportions. None of the Fonera's components ever receive 5v, and the actual wi-fi block's power is dropped down to 2.8v or something.

Weird.

Oh, I remember why the Fonera draws less current at 3.3v versus 5v:

For whatever (stupid) reason, the Fonera's official DC input jack requires 5v. It comes with a 5v, 2A wall wart. As soon as the voltage comes through the jack, it is immediately run through a 3.3v voltage regulator, which (presumably) sucks up more current and (undeniably) gives off heat waves of hellish proportions. None of the Fonera's components ever receive 5v, and the actual wi-fi block's power is dropped down to 2.8v or something.

Weird.

AFAIK, this is very normal. When you need a clean 3.3 V output, you have to use a voltage regulator. But a voltage regulator requires to be powered with a voltage superior to the one it delivers, so your router requires a 5V input in order to internally deliver a clean 3.3V

Wow, you guys are quick :D

I'm not sure about that 9v/1A adapter, but it's a moot point now that I'm going to order the 5v/1A and split it, per your suggestion.

:-/ Wow, I really need to pay attention in the electricity unit of my physics class next year. I thought that 1A meant it was putting that out all the time...

Stupid question: do you have any specifics as to how I should go about splitting it, or is it pretty hard to screw up?

dylpkls91,

You would definitely split the adapter's output.

I'm surprised to hear that the voltage regulator got hot - even at 9V - assuming you connected it to the power jack. If you put 9V to the Vcc pin, your lucky it didn't fry it. Even then, I'm surprised to hear that the voltage regulator got hot.

Now I am a little concerned about the regulator. I often use "Arduinos" I make myself and they don't have a voltage regulator on them. So as I write, I have plugged my Decimila into 5v on the Vcc pin. Let me check . . . . OK, regulator is cool! (I have the jumper set to EXT.)

I'd bet that Sparkfun wart would work, and it would be simplest.

Hopefully, "smart guys" will weigh in regarding possible effects on the regulator when 5V is directly applied to Vcc, but I'd be surprised if it's an issue.

Cool project BTW. I was wondering if a wireless router would work with a networked Arduino.

Just split both wires to two pairs of wires, using screw connectors (don't know if this is the right word in English, I'm referring to this : http://mike.f.free.fr/domino.jpg upper right side)

Then bring one +5V/GND pair to the Arduino, and the other to the router, eventually mounting back the plug with another screw connnector (see above)

(btw, if someone can give me the correct English name of these things... :))

@BroHogan

It’s not really networked per se, but I can stick the Arduino + Fonera anywhere, connect it to a wifi network, and read and write to/from a TCP port that forwards to and from the Arduino’s serial/softwareserial port. In effect, it’s a tcp-ip to serial two-way bridge.

I’d be happy to give you more details if you want, just let me know. When I am finished with this project I plan to properly write it up.

I once powered my Arduino using a 1A power supply (but 9v not 5v), and the voltage regulator on the Arduino board got dreadfully hot and began to smell like it would combust any second.

What were you trying to power from your Arduino while you were doing this? Linear regulators like the ones on the Arduino dissipate power equal to:

(Vin - Vout) * output current

These regulators are limited by the power they can safely dissipate (which is often why you can improve their performance with a heat sink), so the higher the voltage you put in, the less current you can safely get out. If at 9 V you were trying to power something like your router from the regulated voltage, you could have been trying to pull way too much current, which would have heated the regulator up substantially. Often regulators have thermal shutdowns that protect them, which is probably why you didn't break anything.

  • Ben

That's the odd thing: with the 9v/1A supply, I powered both the Arduino and the Fonera for about ten seconds. Then, when I realized that the Fonera wasn't going to boot, I disconnected it and left the Arduino on its own for another five minutes or so. That's when I realized how hot it had gotten, and how it had taken on that dangerous hot electronics smell.

But the good news is that it doesn't matter that much now...

Well, 10 seconds is still a pretty long time to be dissipating ~4 Watts in such a tiny package. I'm glad everything still seems to be working.

  • Ben

Just split both wires to two pairs of wires, using screw connectors (don't know if this is the right word in English,

I'd probably call that a terminal block, YMMV. :)

--Phil.

Just ordered from Sparkfun- one 5V/1A wall wart and one female barrel jack, for soldering to.

Thanks guys! I expect this to work out fine, as long as the Arduino will function correctly powered by 5v at its Vcc.

Can you post information about how you connect arduino and fonera, like code, etc?