I don't know how it should work. For getting digitalWrite(9, light) to work first pin9 has to be defined as output: pinMode(9, OUTPUT). This line is commented out! digitalWrite(9, light) can only switch pin9 on or off, on if light is HIGH, off if light is LOW. I think that analogWrite(9, light) (after defining pi9 as output) would make a better job because "light" can be a value between 0 and 255. But this command doesn't neither work because it uses a timer for PWM and the timer is taken for the clock. Am I right? Isn't it possible to take another timer for PWM? Maybe there isn'T enough flashROM left for this change? ​How can I get dimming work as is?

Thanks a lot for sharing this. Yet it is a bit strange, because libusb0.dll is supposed to be in the same folder as arduino.exe. It has always been there and on my PC it still is. Compiling for and uploading to the Elektor Uno R4 with Arduino IDE 1.8.5 and the Boards package on Windows 10 works perfectly fine for me. Didn't other boards show the same problem?

Could be that your contrast is set wrong.

hi  i used your PCB to make a power meter and used a blue light LCD 1602 but the characters show in black not white in LCD screen ! what should I do? I know that in your layout your are not connected vss to gnd ! do you think there is a problem with my power supply?

I calibrated the sketch with the LDR I use but the display doesn't dim. I checked the values in serial console and they should be right (going from 255 to 1). Any hints where to search the error?