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Topic: 9V wallwart outputing 13.2V with no load Can I use it to power 5 NANOs? (Read 796 times) previous topic - next topic

jbellavance

I have a wallwart that is rated 9V, 500mA. With no load, I read 13.2V on the multimeter.
The other wallwart that I have with the same ratings goes as high as 13.8V

I know that wallwarts have higher voltages when they are not connected, and that the voltage increases. I also read that they get to their rated voltage when sufficient (500mA?) current is drawn.  But at 13.2V, it is more than the recommended 12V for the Nano.

I have attached a schematic of what I have in mind. The wallwart would supply voltage to all the 5 Nanos. I have 4 Nanos that reads inputs and reports activity to a master Nano via i2c. 2 of them also have LEDs as output. Only one of the input device is activated at the time amongst all slaves.

Slave 1 has :
- 1 voltage divider array of 8 switches with pullup of 10Kohms on A0 (Powered by the Nano's 5V pin)
- Between 0 and 9 simultaneously on LEDs with 220ohms resistors.

Slave 2 has :
- 1 voltage divider array of 6 switches with pullup of 10Kohms on A0 (Powered by the Nano's 5V pin)
- 8 rotary encoders with A and B channels plus the switch on 3 busses (INPUT_PULLUP) and 8 individual OUTPUT pins, all HIGH, except when they are read.

Slave 3 has :
- 2 voltage divider arrays of 6 switches with pullup of 10Kohms on A0 + A1 (Powered by the Nano's 5V pin)
- 5 rotary encoders with A and B channels plus the switch on 3 busses (INPUT_PULLUP) and 5 individual OUTPUT pins, all HIGH, except when they are read.

Slave 4 has :
- one and only one of 3 LEDs always on (220ohms resistors).
- 2 voltage divider arrays of 6 switches with pullup of 10Kohms on A0 + A1 (Powered by the Nano's 5V pin)
- 6 rotary encoders with A and B channels plus the switch on 3 busses (INPUT_PULLUP) and 6 individual OUTPUT pins, all HIGH, except when they are read.

Master only manages i2c and communication with the computer. (Nothing connected to it.)

All in all, when the system is idle, I have :
- 6 voltage divider arrays with 10K resistors (5 x (5 / 10000)) for around 3mA
- 19 output pins HIGH (I have no idea on what kind of current this draws if any)
- 3 x 3 pins in INPUT_PULLUP mode (Again, I have no idea)
- 5 Nanos running (5 x 19mA) = 95mA

If I use this wallwart in this configuration, will the voltage drop sufficiently to run safely?

Thanks for your insight.

Jacques
If I can help...

123Splat

Nano's, as I recall, do not have linear 5V regulators on board, so, NO.

5 Nano's in parallel will still se overvoltage and not provide happy results.

MarkT

Is it even a smoothed supply?  I would measure the voltage under a light load with the AC setting
on a multimeter - shouldn't be much AC component.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

jbellavance

Would a L7805 voltage regulator do the trick? and if so, How would I connect it to my schematic?

I am realy a newbie as far as electronics is concerned. I found this, but it does not say how to do it.

Thanks for your help.
If I can help...

IamFof

Jacques

Yes a 7805 would give you a fixed 5v you could put into the 5v pin.

Get the data sheet and read it through.  It will tell you in there that you need a capacitor on the I/P and another on the O/P. Use the values they specify.

The data sheet will show you how it connects, which would be, in your case, the +v from the wallwart to Pin 1, the -ve to Pin 2. Also a wire from Pin 3 to the Nano 5v I/P and another from pin 2 to Nano Gnd or 0v.

DON'T forget the caps between 1&2 and 2&3.

The 7805 will give max 1A (some claim 1.5A but treat all as 1A max).  Currently you are going to draw approx. 100mA. Let's say the wall wart, at this point, is actually giving 9v. You will therefore be dissipation 4v*100mA = 400mW.  Nothing to worry about. BUT what are you going to add to it and what current will they require. That will increase the dissipation and therefore the 7805 could start to get hot and need heatsinking

Better to buy a cheap buck regulator from ebay or other suppliers. Arduino Shop???
Connect the wall wart wires to the buck, attach DMM to O/P.  Adjust onboard trimpot to give 5v O/P.  Connect to Nano.  No heat worries.

Good luck

Fof

jbellavance

Hi,

is this what you are talking about?

I have never heard of buck regulators before. That sounds fantastic.

Thanks

Jacques
If I can help...

jbellavance

Hi all,

I went back to Arduino Nano's page and I find in the technical specs the following:
Quote
Input Voltage   7-12 V
But further on the page, in the Documentation, Power section:
Quote
The Arduino Nano can be powered via the Mini-B USB connection, 6-20V unregulated external power supply (pin 30), or 5V regulated external power supply (pin 27). The power source is automatically selected to the highest voltage source.
For a non-technical-background fellow like me, there is a huge difference between 12V and 20V.

If the Documentation/Power section is to be followed, I could use the wallwart on Vin (pin 30).

If the Technical specs section is to be followed, then all the previous discussion was pertinent. I would use the buck regulator and I would supply the Nano on the +5V pin (pin27) and not on the Vin pin which needs at least 7V to operate.

Where could I find what is the proper Power requirements on the Nano?

Thanks for your insights all.

Jacques
If I can help...

CrossRoads

"Where could I find what is the proper Power requirements on the Nano?"
Technically, on the datasheet for the 5V regulator on the board.

Practically, 13.2V will work, but the regulator may overheat and go into thermal shutdown if you try and draw very much current, like more than 100, 150mA.  A 7.5V or 9V regulator would  be better.
http://www.dipmicro.com/store/DCA-0910

Use a multimeter and measure the wallwart output on AC mode, see how much ripple there is.
There shouldn't be much.  If there is, get a different wallwart, one with a regulated output.


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.

jbellavance

Hi CrossRoads,

How do I measure ripple with a multimeter? (I won't ask why, it is more than likely way over my head)

How do I know that a wallwart is a regulator or not. The word Switching?

Thanks

Jacques

If I can help...

CrossRoads

Put the meter in AC voltage mode and measure from the output to Gnd.

Switching regulators will be regulated.
13.2V may just be transformer going thru 2 diodes or a diode bridge with some caps for filtering.
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.

jbellavance

Hi,

Just did that and it reads alternately between 5.35V and 0V.

I don't know if it is "good ripple" or "bad ripple"

Anyway, I feel that I should go ahead and get a switching regulator to be on the safe side.

Thanks for your help.

Jacques
If I can help...

Wawa

Nano's, as I recall, do not have linear 5V regulators on board, so, NO.
Yes, they do. But heatsink area is very small.
>9volt on V-in and a few sensors/LEDs might already be a problem.

@ OP.
Unregulated supplies are bad news for electronics. Don't use.

You already have I2C wiring.
That can carry 5volt power from the master to all 5volt pins of the slaves.
No need for extra supplies.

What sort of cable are you using, and what is the total length.
That, and the right value pull up resistors, might depend if your I2C project will work
Leo..



jbellavance

Hi Wawa,

On a Nano, i2c is on pins A4 & A5, one as a clock, going HIGH and LOW and the other one as DATA, also alternating between HIGH and LOW. I don't see how I could supply 5V via those pins. And I understand that a pin can only supply 40mA.

As for the cables (between the Nanos) is 22 ga unshielded wires fo a total length of 14".

Jacques
If I can help...

IamFof

Hi Jacques

The Pololu look good, though I would be concerned re their comments about how hot it gets.  The ones I've used for years are these type:

http://www.ebay.co.uk/itm/LM2596-Step-Down-Converter-3A-Adjustable-DC-To-DC-Voltage-Regulator-Buck-Module-/172597952784?hash=item282fa3c110:g:WqUAAOSwzgBY2ikW

Although they claim 3A, I try to never draw more the 1A - 1.5A.  No ideas as to the QC of the manufacturers or the genuiness of the regulator.  Saying that, though, I have never had a problem with them.

Fof

jbellavance

If I can help...

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