I have code that works using Arduino.

Because I wanted to size down the project, I replaced it with an Attiny841.


I soldered the 841 on an adapter and checked all pins using a multimeter for cold joints.

Then I connected the pins using this schematic from http://elecrab.com, but with a cap for RESET in addition:

enter image description here

I used the online Arduino environment to burn the ArduinoISP sketch to my Arduino.

Then I used the offline Arduino program, using ATTinyCore as such:

enter image description here

I burned the bootloader and it did so succesfully.

I then copy-pasted my own sketch in the offline environment and uploaded it, which also worked without a single error.

(For some weird reason I cannot burn the ArduinoISP using the offline program, hence the two-step method.)


I left my sketch unaltered, except for the selected pins which became:

#define BEAM_One 2
#define BEAM_Two 3  

#define LED_Install 4
#define BUTTON_Install 5 

#define AT_Mode 6
#define POWER_On 7

#define LED_Occupied 10

Basically, I thought, 841 physical pins 11 and 12 are TX/RX and 2 to 4 are special cases, so I can simply select pins 5 to 10 and 13 for I/O.

I then choose the above pins, using the pin mapping in the ATTinyCore documentation:

enter image description here

ATTinyCore already preconfigures PWM, so it can be used without any extra steps or coding, I read somewhere.

Physical pins 5 and 6 allow for attachInterrupt(), see PCINT10 and PCINT7 on PB2 and PA7.


I connected some LEDs at the 841's output pins.

Some don't react, which might be due to a cold joint.

However, others do react but not in the expected way.

The LED connected to 841 pin 10, or pin 7 in the Arduino code, should go HIGH, then LOW, then HIGH with noticeable delays. In reality, it is HIGH and stays that way.

The attachInterrupt() functions are something else still. I think I just figured out that I am trying to use INT on PB2 and PA7, but it only exists on PB1 contrary to Arduino. I can use PB2 and PA7, but those are PCINT, that change ports and only use CHANGE (not RISING or FALLING). I hope to fix this specific issue by using this library: https://github.com/NicoHood/PinChangeInterrupt.

Does anyone have a clue what the issue might be with the pins not reacting as expected?

Thank you for reading my small novel.

  • \$\begingroup\$ Before burning codes like interrupts involved, did you try to implement a simple switch and led circuit or a serial communication project and able to prove that your whole setup you crafted out is 100% right ? \$\endgroup\$
    – Mitu Raj
    Commented Aug 30, 2019 at 18:17
  • \$\begingroup\$ In my code there is a blinking LED also on a designated pin (setup has a certain power on and off routine to get to AT mode of a Bluetooth module). That's the standard example always used. I don't see why that wouldn't be good for testing. I mentioned it in my post. Programming chips on breakout boards with Arduino is also cumbersome. \$\endgroup\$ Commented Aug 30, 2019 at 21:47

1 Answer 1


Solved. Pin mapping had to be counterclockwise, selected under Tools when burning the sketch with Arduino.


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