Any explanations for the initial transients in the BLINK project

I am very new to Arduino and I was just able to upload a Blink project. As soon as I start debugging there appears to be at least two transients before the program settles down to blink as programmed. I am seeking explanation for the transients.

I am using Arduino UNO with Arduino IDE or Visual Studio 2013 Community edition.

By "Blink project" did you mean the sketch File->Examples->01.Basics->Blink?

Thanks. Yes. That is correct.

Please describe the "at least two transients" in detail. When do they occur? How long are they? What voltage? What instrument are you using to measure them?

When the chip first receives power all digital I/O pins are reset to INPUT. Because of the high impedance of inputs the pin is left to float.

If the reset was manual (pushing the button) the Arduino UNO bootloader sets Pin 13 to OUTPUT and the reset had cleared the data register so the pin should switch from floating to LOW. The bootloader then turns Pin 13 on and off six times (3 blinks of the LED).

When control passes the the Blink sketch the pinMode() in setup() sets Pin 13 to OUTPUT but since it is already an output that should not cause any transients. The loop() function then almost immediately turns Pin 13 HIGH and the blinking sequence starts.

Connecting with Serial Monitor will cause a Reset which may introduce more transients.


I am sorry, I do not have measurements of any kind as no measuring instrument is hooked up. My question was based solely on observation. I see two flickers, one after the other before the circuit gets into the rhythm of the program.

There are no push buttons in the circuit. Just the LED and the resistor. I will check this out, it may be because of 'Serial Monitor will cause a Reset '.