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Author Topic: UNO board doesn't work unless monitor is running  (Read 617 times)
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Has anyone seen this issue... I have an uno board, connected to windows XP.  I am connected with the USB cable with a simple connection of three wires in ports 2,3,4 that are running to 2 - 8 bit shift registers running 16 LED's.  I am creating a binary clock.

The code runs through shifting the registers based on the time.  When I am connected through the USB it will upload and try to run.  The lights will start flashing and then it seems to reset and flash again, over and over.  If I open the serial monitor it then runs correctly.

If I unplug the USB and then run it off of a 9v power supply it also runs correctly.

Any ideas?
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Not without seeing your code & schematic.
Could be overtaxing the 500mA available from the USB. Not sure why serial monitor would help that.
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