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Topic: external feed or PC feed ? (Read 3318 times) previous topic - next topic


Hi there,

I did a project right here to a device that control 3 sensors and it will be used in the railroads of my city.
I just have one trouble with that, when i plug my arduino UNO on PC it is working pretty fine on the board, but this project is for railroads and I need it to work with bateries. My batery system is working because the red light of my arduino uno turns on but anyother thing happen. I mean my display does not turns on and even my sensors.
Does arduino have any problem when you use an external feed ? Is there anything that I can do to fix that ? Anyone else had that problem ?

Thanks so much for your attencion and I ll be glad for any help that you can provide.

Best regards.


Maybe your battery doesn't have enough voltage or current to supply all your hardware.

Can you describe what battery you're using, what other hardware you have attached to the Arduino and how it's all connected?



I am using 2 series 12V bateries to have 24V output (because one of my sensores requires 18-30v)
Then i am using a 7818 (for 18V), a 7812, a 7808, and finaly a 7805 for the arduino, one sensor and the display.
The output level of the 7805 is 4,7V ... is that 0,3v a problem for the display ? how can i have 5v then ? i have tried a lot of diferents 7805 just to be sure it is not a chip problem


A good detail is ... the 7818 is working pretty fine and the sensor that requires 18v is working.


are you using all those regulators to step down the volts incrementally to get to 5v? or each regulator is serving a device/sensor at that regulators voltage?


I am using incrementally to get to 5v ... if u connect just 18v to 5v the 5v one will broke right ? But yes in the project i just need 18v and 5v


You aren't feeding 5v into the barrel plug on the arduino are you? Theres already a 5v regulator on that input. You ca't directly power it from the 24v source though, you would need to drop the voltage down to somewhere between 8v and 12v.


OK, so it's 4.7v not 5 and I think your only chance is to apply that directly to the 5v pin, thereby bypassing the local supply circuitry. There was recent discussion about this and you should trawl for that.

One thing you can be sure about is that, if you are feeding 4.7v into the standard 2.1mm power socket, you are wasting your time. My 5.3v phone charger isn't up to that, and I guess when they say 7v minimum, they really mean it.,  


i thought lm317 adjustable regulator takes in up to 36vdc. that might free up some space using just that to regulate.

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