Here's is what i have in mind (see attached drawing for clarity) :
The first Arduino is supplied with 9V (this is necessary because it carries a shield that demands 9V). The second Arduino (aslo carrying a shield) is fed by the first Arduino via the 5V and ground pins. Then comes a third circuit (an audio amplifier with speakers), which is also fed the same way, that works at 5V and demands about 4W.
So, my questions are : is this safe (does the 5V pin has a current limit) ? If not, what can I do (else than buying a second supply) ? Note that the 9V supply itslef can delivery up to 2 amps.
ps: I know i could have worked my project out with a more pin-y board, but I had plenty of Uno's at hand.
Pretty much everything has a current limit. In this case, the one that you'll probably hit first is the arduino voltage regulator's ability to deal with the heat. How much current are you attempting to pull through the arduino's power supply? You'll need to find some other way of powering the third circuit at the very least. Things are going to get pretty hot if you try to draw 800ma through an arduino. Since the 9v supply can probably power everything, all you really need is a 5v regulator that can handle the amount of current that you're going to be using. The 5v regulator can then power everything except whatever the first shield is that requires 9v.
So, if I continue to power the fisrt Arduino with my present 9V supply, then take the 9V from the first Arduino's Vin pin (which is the raw input, right?), put it in the regulator, take the 5V output and pour it into the second Arduino and the amplifier (parallel wiring), it will work ?
And, about the regulator itslef, is this what i'm looking for ?
[quote author=Mad physicist link=topic=161722.msg1209306#msg1209306 date=1366479182]
So, if I continue to power the fisrt Arduino with my present 9V supply, then take the 9V from the first Arduino's Vin pin (which is the raw input, right?), put it in the regulator, take the 5V output and pour it into the second Arduino and the amplifier (parallel wiring), it will work ?[/quote]
Assuming the regulator you use can handle 800mA, then yes, it should work.
That is a good choice. It is a switching regulator which is very efficient for use with high current loads like you are using.
what about using the 9V supply to power the 2 arduinos (parallel wiring) , then take the 9V from the 2nd arduino (or the 1st, doesn't matter), put it in the regulator, which 5V output will power the ampli ?
This way, you make sure your arduinos are well and 'independantly' powered , and the regulator is only used for the device that needs a 5V supply
alnath:
what about using the 9V supply to power the 2 arduinos (parallel wiring) , then take the 9V from the 2nd arduino (or the 1st, doesn't matter), put it in the regulator, which 5V output will power the ampli ?
By connecting the Vin pins of the Arduino together, it is effectively putting them in parallel anyway.
The problem is that the on-board regulator (of either Arduino) is still working with 9V in and 5V out at 800mA. That's too much power for the on-board regulator to dissipate.
By connecting the Vin pins of the Arduino together, it is effectively putting them in parallel anyway.
The problem is that the on-board regulator (of either Arduino) is still working with 9V in and 5V out at 800mA. That's too much power for the on-board regulator to dissipate.
[/quote]
Yes, but you said you planned to "connect the 1st arduino, with 9V, then Vin(1st) --> Extern-Reg_In -> ExternReg_Out5V -->[Arduino(2nd) AND Ampli ]
I suggest : connect Arduino(1st) with 9V, then from Vin(1st) -> Arduino(2nd), then from Vin(2nd) -->Extern-Reg_In -> Extern-Reg_Out5V --> Ampli
This way, the 2nd Arduino is supplied with 9V (which is not the case in what you described)
as you can see, you still use the external regulator, but only for the ampli
alnath:
I suggest : connect Arduino(1st) with 9V, then from Vin(1st) -> Arduino(2nd), then from Vin(2nd) -->Extern-Reg_In -> Extern-Reg_Out5V --> Ampli
This way, the 2nd Arduino is supplied with 9V (which is not the case in what you described)
My main point was that your approach still doesn't solve the problem. An Arduino board draws less than 50mA, less when you aren't using the on-board voltage. So powering board-2 off of board-1's regulator isn't the issue.
Step 1. Buy a 5v regulator.
Step 2. Use the 5v and Gnd to VIN and GND.
From this point on, you then simply share off of those 2 (VIN/GND) via breadboard to power all your other arduino's, but it has to be in VIN, avoid the onboard regulator.
The Arduino Uno can be powered via the USB connection or with an external power supply. The power source is selected automatically.
External (non-USB) power can come either from an AC-to-DC adapter (wall-wart) or battery. The adapter can be connected by plugging a 2.1mm center-positive plug into the board's power jack. Leads from a battery can be inserted in the Gnd and Vin pin headers of the POWER connector.
The board can operate on an external supply of 6 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may be unstable. If using more than 12V, the voltage regulator may overheat and damage the board. The recommended range is 7 to 12 volts.
The power pins are as follows:
VIN. The input voltage to the Arduino board when it's using an external power source (as opposed to 5 volts from the USB connection or other regulated power source). You can supply voltage through this pin, or, if supplying voltage via the power jack, access it through this pin.
5V.This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.
3V3. A 3.3 volt supply generated by the on-board regulator. Maximum current draw is 50 mA.
GND. Ground pins.
IOREF. This pin on the Arduino board provides the voltage reference with which the microcontroller operates. A properly configured shield can read the IOREF pin voltage and select the appropriate power source or enable voltage translators on the outputs for working with the 5V or 3.3V.
It would work, the Regulator would not be happy but the track is shared.... place >5v in VIN, you'll fry the MC. I don't see any protection other than a single diode after it passes through the voltage
regulator... so my method would still work.
cjdelphi:
So VIN goes through the regulator does it?.... Because VIN is a direct source to the 5v USB + line...
No it absolutely does not. It is connected to a power selection circuit that determines if the 5V node is powered by USB or the on-board regulator. It is exceptionally clear in all the official Arduino schematics.
cjdelphi:
infact, this is what I was looking for Take a look at the VIN Track.
I haven no idea what that circuit is suppose to be, so I fail to see how it applies. If you are going to answer questions related to the Arduino, use Arduino resources. Do not find corner cases AND make an incorrect argument. That circuit shows the Vin connected to a header which is apparently used to manually select how the 5V line gets powered.
The simplest, an, IMO, the best way is :
Use a 9V power supply to connect both arduinos AND the input of a 5V external regulator (say a 7805 ).
The output of the regulator will power the ampli.
(that is what I really meant in my 1st suggestion, but maybe it wasn't clear .... sorry, I'm french )
OK, you'll have to add a jack : solder 2 wires ( one + and one Gnd) to the existong jack and you're done
