Pages: [1]   Go Down
Author Topic: Clarify USB Comms + External Power on UNO  (Read 398 times)
0 Members and 1 Guest are viewing this topic.
Dubai, UAE
Offline Offline
Edison Member
*
Karma: 21
Posts: 1670
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Hi,
    I would be grateful if anyone who has tried it can confirm that a UNO can be simultaneously connected to USB for serial communication and an external source for power.

    I know that the UNO Automatically selects the power source, but which has priority and are they isolated once one is selected.

Thanks for any advice

Duane B
Logged


Manchester (England England)
Offline Offline
Brattain Member
*****
Karma: 506
Posts: 31345
Solder is electric glue
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

The external input is switched to power the unit if it is available. The two supplies are not isolated, that word implies the grounds are sepreate, they are not.
Logged

Dubai, UAE
Offline Offline
Edison Member
*
Karma: 21
Posts: 1670
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Hi,

Thanks for the quick response, I will rework my project to use this approach.

Thanks,
  Duane B
Logged


Dubai, UAE
Offline Offline
Edison Member
*
Karma: 21
Posts: 1670
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Hi,
   I have the UNO powered from an external LIPO battery and sending data to the PC through USB, its as simple as suggested. This kind of simplicity that makes Arduino a joy to work with.

   I am making a point of connecting the external power first, I am assuming that if I was to connect USB First, that would initially supply power, as soon as external power becomes available some sort of switch would take place. As I am unaware how this is managed and any of impact it may have I am avoiding it.

Thanks
     Duane.

Logged


Manchester (England England)
Offline Offline
Brattain Member
*****
Karma: 506
Posts: 31345
Solder is electric glue
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
As I am unaware how this is managed
On the board is a voltage comparator. It takes the USB voltage and a fraction of the external voltage, which ever is higher determines the output of the comparator. This is then fed to an FET to switch the appropriate voltage to the main board. I don't think there will be any issues doing this while the board is running.
Logged

Pages: [1]   Go Up
Jump to: