I have an arduino UNO running a couple of Dallas thermometers, an RTC breakout, SD card reader breakout, an XBEE wifi module and a couple of 5v relays. The whole setup consumes about 250 Mili Amps...
Here's the odd behavior and I can't figure out WHY its happening:
I can operate the whole setup from en external phone charger connected to the USB on the arduino.
I can operate from my computer's USB connected to the USB on the arduino.
I can operate from an external battery pack (6 AA batteries) connected to the arduino jack.
However, when I use a 2amp 12V external power source connected to the Arduino's Jack, everything runs EXCEPT the xbee wife module. The Xbee will not connect to my wifi network. When running on the external 12v source, the voltage drops to about 11.8V, does not overheat or appear to be damaged or anything...
If I run BOTH the external 12V power source AND the USB connected to my computer or the phone charger, everything works fine.
So, obviously the external power source is at fault and needs to be replaced... Question is Why?? I have had this kind of problem before with other power sources and would like to know how to avoid it in the future
Did you measure Arduino's 5volt and 3.3volt supply pins.
If they are ok, I don't know.
Maybe the power supply wiring changes your WiFi footprint.
How far away from the router.
Did you try turning/moving the WiFi module.
Leo..
TomGeorge:
With USB and 12V, you are turning the 12V off because of the internal switching circuitry on the arduino board, and just running on USB
Tom.....
Interesting... I was under the impression the Arduino would use the highest voltage supplied. So if a 12V was supplied via the jack and 5v via the USB, it would pick the jack...
Did you measure Arduino's 5volt and 3.3volt supply pins.
Hi Leo,
I just measured the 5V pin and got some interesting results!
Powered from the external phone charger: voltage settles to about 4.7 after several minutes of operation
Powered from the 12v power supply: voltage starts at 4.99V and then, after about 4-5 mins drops to 3.52V... It also explains why the xbee continues to transmit for a minute or so and then shuts off!
I am not using the 3.3V pin, but when powered from the phone charger, its a steady 3.33V
Thanks for the heads-up... I will keep this in mind for future
Its obvious the 12V power source is bad and I will be tossing it out.
What the problem is, you have too much load on the UNO 5V regulator.
As time goes by the regulator heats up.
The regulator then lowers its output voltage to lower the load current to stop over heating, that is why you see the 5V go down to 3.25V.
The regulators have built in thermal protection.
Try a 9V supply, but you will probably have to provide a separate 5V supply for some of the hardware connected to the UNO to take the load off its 5V regulator.
You say its probable the 12V source itself is ok and the Arduino's internal regulator is being overworked when the power source is connected to the Arduino power jack - that makes sense to me !
Now, my confusion stems from the from the fact that I used a 9V external battery connected to the same jack and the setup worked perfectly.
Are you saying that at 9V the Arduino's regulator has to work less hard and thus it does not "suffer" as much? Theoretically, if I used a DC to DC regulator to go from the 12V my source provides, to say 7 volts, will my problems go away?
Again, thanks for your replies! I have learned a lot!!
Wawa:
A true tech would change the feedback resistor in that suppy, so the supply would output 9volts.
Well, problem solved!! I need the 12V that comes out of the power source to run a gas solenoid valve so I could not replace the power source for a 7V one as suggested...
What I did is place a step down converter between my 12V power source and the Arduino. The Arduino now gets 7V, its running cool and has been operating for about 120 minutes without crapping out!!
I had another project running an ethernet shield I was about to toss out due to the same problem!!
The project I am building allows my solar water heater to connect to emons.org allowing me to view temperatures from the internet. I built the first Arduino based differential controller 19 months ago and right now I am building version 2.0
phamilton:
What I did is place a step down converter between my 12V power source and the Arduino. The Arduino now gets 7V
If you want to be even more efficient, let the DC-DC step down the voltage to 5V and feed it to the 5V pin. This way the on board regulator is bypassed completely so no heat at all. And all 5V stuff can connect to the DC-DC right away so you're not limited by the on board regulator at all.
