Quick question - the specs state "The Arduino Uno can be powered via the USB connection or with an external power supply. The power source is selected automatically."
How is the power source selected automatically?
Is there an in-chip relay? (perhaps thats a stupid question...)
Or some tiny SMD components which handle this? (ditto)
The reason I ask is, as you have probably read, I'm working on a solar power monitor.
Instead of auto-switching between USB bus and DC power, perhaps I can make use of this feature to auto switch between (solar powered) battery and DC input.
Quick question - the specs state "The Arduino Uno can be powered via the USB connection or with an external power supply. The power source is selected automatically."
How is the power source selected automatically?
The board has a simple two resistor voltage divider wired to the Vin voltage, if there is a voltage of sufficient voltage, a op-amp comparator circuit switches off a MOSFET switch that then isolates the USB voltage from the board's Vcc bus. So if there is both USB voltage and Vin voltage available, then the Vin voltage takes priority and is used to power the board.
Is there an in-chip relay? (perhaps thats a stupid question...)
No, just an op-amp circuit driving a MOSFET used as a switch.
Or some tiny SMD components which handle this? (ditto)
The reason I ask is, as you have probably read, I'm working on a solar power monitor.
Instead of auto-switching between USB bus and DC power, perhaps I can make use of this feature to auto switch between (solar powered) battery and DC input.
Perhaps, but it would probably be better to design your own auto-switching between solar power and battery power externally and then wire the resulting selection voltage to the arduino external power connector. External allowable voltage input is is around 7.5 to 12 vdc. Lefty
One more thought is that since the regulator on board is a linear it is best to keep the power to the DC in to 7.5V.. Less power wasted as heat. For best efficiency
(less power lost to heat) use a switcher to provide the power to the Uno DC in... Or provide direct +5V to the board from the same switcher... Either way will work. I use both methods... I have an Uno connected to a breadboard through a cable header and shield (From Liuder Via Inmojo)... The Uno is powered from the USB port and the breadboard has a linear board that plugs into the breadboard for the breadboard only and is powered by an external PSU. The grounds are of course common.