Arduino Uno Bootup issue

Guys:

Just got a minor problem with my arduino Uno board. Everytime i plug in the usb cable or connect using terminal program, the Uno reset and its fine for me (knowing that it is the DTR line issue). I have two limit switches as input and i just found out that if either one is activated (ie, the pin is pulled low) as i plug in the usb cable, the Uno would not bootup and neither when i connect using a terminal program. I have to manually trigger the DTR line and the Uno would boot up probably. I wonder if it is due to the fact that i am using the usb power to pullup thru a 4.7k resister to the input pin. Thanks in advance guys.

Sunny

What pins are the switches on? D0, D1?

I believe it is D6 and D7 on the UNO

That is odd then. Those pins should no impact on booting up.

I am starting to think maybe i should just cut the reset-en trace......

schan117:
I am starting to think maybe i should just cut the reset-en trace......

First try a quick little test. Wire a diode from +5vdc pin to reset pin, with anode connected to the reset pin. This is a fix the arduino installed in the latest R3 Uno board to prevent a latch-up problem when the auto-reset function is activated. It's a obscure problem but does follow the symptoms you are seeing.

Lefty

Thanks for all the input guys, FYI, i cut the RESET-EN trace and the UNO is able to bootup with D6 or D7 pulled low. Guess this confirmed it is a RESET issue. I am going to try the diode as Lefty suggested.

Sunny