I don't see anything to indicate that it is hardware related. The op amp amplifier circuit has an RC low pass filter on the output but that doesn't explain the latching behavior you describe. My guess is it is software conflict somewhere. Have you considered the possibility that you are using too much ram in the ATtiny85 ? It only has 512 bytes of internal SRAM. You might be expecting too much. Did you write the code ? Do you understand it enough to modify it so it only does a simple on/off function for the leds instead of a fancy pattern ? Can you comment out a bunch of stuff and just stick in a simple statement that turns them on so that we can verify that it is not the leds per sei , but rather the side-effect of running the led code (like filling up ram). The other possibility is that it is NOT what the code is doing , but the speed it is doing it , ergo TIMING issue. Put delays in it for debug purposes. Ignore the light pattern and just concentrate on getting it to work by slowing it down with delays. If it doesn't lock up with the delays then I think you have found your cause. Forget about what you want the system to do and focus seeing what you can do to stop it from locking up. The first place to put a delay is right after the analogRead. I know you're using millis because you don't want any delays but that isn't working for you is it ? You need to think about what is the connection between the timing and the millis() statements and the analogRead(). You may be filling up the SRAM with your use of millis(). I don't know. I'm just throwing stuff out there. The person who could tell you , if anyone could is PaulS. He's a real Guru but like all gurus, he's very particular (I don't think "picky" quite describes it) If you ask for his help , you better be prepared to follow his instructions to the letter if you don't want to get dropped like a hot potato.