How to determine if ardu is running stable with that powersource

Development Tools IDE 1.x
1

Hi,

i have a power source that can be switched to 6,5V 9V and 12V. I know minimum should be 7V.

How can i see if also 6,5V would be fine too?

The lower the powersource voltage the lower the heat dissipation of the voltage regulator, thats why i want 6,5V

2

See how the Arduino 5V output is with 6.5V vs 9V vs 12V.
How that really goes will depend on how much is drawn from (the demand upon) the Arduino 5V supply.

3

As I recall, the Uno (at least) employs a voltage divider on Vin to work out whether to use the USB as a power source or the power jack. It compares Vin/2 to 3.3V, so Vin would need to be 6.6V to not trigger the test. It may not matter too much if you don't have anything plugged into the USB port.

4

That 6.6 minimum voltage to switch to external source is after the series polarity protection diode from the external power connector, so you really need like >7.2vdc or so at the connector for proper operation.

Lefty

5

I knew about the diode when I wrote that, which is why I said Vin and not "the external power jack", but thought "why would they say 7V minimum when it is really 7.2V?"

I suppose 7V is close enough.

As I read the schematic though, you don't really switch the external "in", it is more like switching the USB "out" if Vin is above 6.6V. I could be wrong.

6

As I read the schematic though, you don't really switch the external "in", it is more like switching the USB "out" if Vin is above 6.6V. I could be wrong.

That is correct, the external voltage if available and of sufficient voltage, overrides and shuts off the USB voltage source if present.

7

lax123 want to know what is the minimum voltage if no USB source. it should be safe to judge by your 5v resource loading i think . just measure the 5v output with multimeter or oscillometer and see if the 5v is stable. it depends not only on your power source voltage, but also on your 5v loading.
by the way , i think it would be safe to input 7v voltage at least , it would not lead to a big temprature problem i think.

8

thx, i will check that.

I only have 6,5V 9V and 12V. So with 9V its getting quite warm.