Based on my breadboard design I created a schematic in KiCAD, designed the PCB and ordered from ALLPCB.

The board:

It arrived in a week:



Started to populate it - here comes the problems:

• I chosen a wrong size package for the ATTINY85, so I have to bend the pins to be able to solder in
• The micro USB connector wasn't far enough from the edge
• The 3.5 Jack had two missing holes.

Those was easily correctable.
So the build (without the display):



After resoldering the ATTINY for a few times, I was able to download the code, but nothing appeared on the display or the LEDs.
Scratching my head. Then I realized, that the ISP connector has all of the pins required to drive the TM1637. So I connected this external display to it:



It was working.
I started to measure the board, and instantly realized the problem.
The VCC and GND pins of the TM1637 was swapped. How this happened?
I mirrored the TM1637 part in the KiCAD. After this the GND pin went to the top of the drawing and the VCC to the bottom. After this I connected the power pins as usual. The VCC to the top and the GND to the bottom. IDIOT!!!!