Can I power an arduino from the 5v on a shield.
What i have is a module that attaches to a device that provides 24vdc power. I am using a xb shield and a proto shield for prototyping my product. can i power the arduino uno back through the 5v on the shield.
You can power the Arduino (Uno) directly on the 5 volt and gnd pin. BUT!!! You have to make sure that it stays that way. The is no protection for the chip if the powersupply goes into the dangerous voltage region (above 5.5 volt).
Also, when you want to use the USB port it depends on what sort of powersupply that 24v DC is and if the output is mains earth referenced. Or that mysterious device is that converts 24 volt to 5 volt. There should be isolation from mains-earth on the negative supply output. If there is a conductive path between the negative output wire and the mains-earth wire of the powersupply input cable then there may be a voltage difference between the USB port GND and the supply negative. That can damage the Arduino, power supply, the USB port or worse your entire computer. When the powersupply is unplugged, you can test that by measuring resistance trough the power supply output minus and the earth-pin on the supply input plug. If there is infinite resistance then you are safe. Check to make sure this is not dependant on the power switch (or output-enable switch if there is one). But do this when it is unplugged from the wallsocket!!!
Well, it probably won’t come to sparks flying right away if you connect powersupply minus to Arduino /USB ground. But if you mess up while prototyping and create a low resistance path from the positive external supply to the Arduino ground directly then bad things can happen to any of the devices in the loop.
The following video talks about hooking up an oscilloscope and how you can blow it up but it could equally apply to this:
Thanks for your reply
since i won’t be using the usb port during operation and only during programming that would not be a problem
David