Using old NXP HEF4094BP shift register chips, for the reason of fixing some old hardware. These chips were popular in the 90's because they could accept 3-15V VCC and directly drive series+parallel LED chains. Think: gas station price signs, etc.
I'm green. Using this post and the 4094 datasheet, I've successfully modeled your typical shift register count-to-100 binary, with an LED on each SR out. Powered by 5V, works great. This was phase 1 for me.
For phase 2, I powered the Arduino via 12V (via p30, Vin). Still supplying 5V to the 4094 (Nano pin 27 output), works great.
Phase 3, I need help. I remove the 5V jumper that was from Nano pin 27 going into 4094's VCC pin. In it's place, I run 12V directly from the (regulated) PS and I get NO LED output. I know I haven't burned anything out because at 12V I get brief "flashes" when I'm "plugging" in the 12V power supply. I can revert to 5V VCC input and it works fine as before.
I've read the datasheet 3X and it's not clear how the chip's output pin voltage is managed when you alter the VCC to be higher (is it limiting current or voltage on the outputs?)