Frequent Questions

184 votes
21 answers
663k views

"avrdude: stk500_getsync(): not in sync: resp=0x00," aka Some Dude Named Avr Won't Let Me Upload My Program

I made an awesome program the other day, and I wanted to upload it to my Arduino. After clicking the upload button, some mean dude named avr came along and stopped me, saying: avrdude: ...
The Guy with The Hat's user avatar
105 votes
3 answers
116k views

Have I bricked my Arduino Uno? Problems with uploading to board

I can't upload sketches to my Arduino Uno. Have I "bricked" it? What steps can I take to work out what is wrong? What can I do to fix it?
Nick Gammon's user avatar
  • 38.9k
135 votes
4 answers
118k views

How can I handle the millis() rollover?

I need to read a sensor every five minutes, but since my sketch also has other tasks to do, I cannot just delay() between the readings. There is the Blink without delay tutorial suggesting I code ...
Edgar Bonet's user avatar
  • 44.9k
21 votes
3 answers
9k views

Classes and objects: how many and which file types do I actually need to use them?

I have no previous experience with C++ or C, but know how to program C# and am learning Arduino. I just want to organize my sketches and am quite comfortable with the Arduino language even with its ...
heltonbiker's user avatar
5 votes
1 answer
1k views

How do you combine 2 different sketches together

(Before you down-vote this, note that it is a "ringer" to answer a FAQ, with a self-answer.) This question comes up all the time. How do you combine 2 different sketches together? Say I have a sample ...
Duncan C's user avatar
  • 5,742
244 votes
13 answers
473k views

Can I program for Arduino without having a real board?

I would like to start the development of some basic Arduino projects but I don't own an Arduino board yet. Is there a way I can write my code and emulate/test it using a desktop computer so after my ...
totymedli's user avatar
  • 2,919
1 vote
3 answers
13k views

My Arduino isn't showing up on my computer. What should I do?

You have your spangly new Arduino board, you've installed the software, and you plug it in. Nothing happens. Diagnosing problems may be a little tricky for the beginner, so what hoops should you go ...
15 votes
1 answer
5k views

What happens when code is uploaded using the bootloader?

When I upload a new sketch to my Arduino Uno using the Optiboot bootloader, what really happens? What is sent to the Arduino? How does it respond? What does "not in sync mean"? What is "in sync" ...
Nick Gammon's user avatar
  • 38.9k
67 votes
2 answers
229k views

How do you use SPI on an Arduino?

With reference to the Arduino Uno, Mega2560, Leonardo and similar boards: How does SPI work? How fast is SPI? How do I connect between a master and a slave? How do I make an SPI slave? Please note: ...
Nick Gammon's user avatar
  • 38.9k
62 votes
7 answers
230k views

Is there any way to download a sketch from an Arduino?

I made a sketch, but then I lost it. However, I uploaded it to the Arduino before losing it. Is there any way I can get it back?
The Guy with The Hat's user avatar
18 votes
1 answer
28k views

How do interrupts work on the Arduino Uno and similar boards?

Please explain how interrupts work on the Arduino Uno and related boards using the ATmega328P processor. Boards such as the: Uno Mini Nano Pro Mini Lilypad In particular please discuss: What to use ...
Nick Gammon's user avatar
  • 38.9k
94 votes
22 answers
19k views

What are the other IDEs for Arduino?

The basic Arduino IDE lacks a lot of the sophistication present in other IDEs such as code completion, code collapsing, folder organisation, etc. Are there other IDEs that allow programming in C or C++...
DLJ's user avatar
  • 1,149
65 votes
13 answers
84k views

Is there a way to have more than 14 Output pins on arduino?

Is it possible to have more than 14 output pins on the Arduino, I am working on a project in which I need to light up several LEDs individually. I only have an Arduino Uno, and I don't want to get a ...
JVarhol's user avatar
  • 1,903
10 votes
1 answer
11k views

Adding a custom board to the Arduino IDE

I would like to know what is the procedure for adding a custom board to the Arduino IDE? My custom board is similar to the Arduino Zero. Instead of using the ATSAMD21G18, my board is based around the ...
sa_leinad's user avatar
  • 3,218
2 votes
1 answer
462 views

Wanted to control 2 servos with serial read [closed]

I want to use 2nd servo only when 1st is in up state by asking user whether he wants to fire or not.(code in bold is not working ) #include <Servo.h> Servo myservo; Servo trigervo; ...
Aditya Raj's user avatar

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