Hi
Is there a need for any more than a simple resistor divider in this situation?
I only have a digital input, and Vcc for the shift register is 5V.
In the real circuit the battery could be up to 13.8 Volts, so I realise the 150K resistor should be a higher value
to prevent the shift register pin ever seeing a voltage above it’s 5V supply rail.
This way I think diode clamping the shift register input can be avoided.
Software ensures this input must read the warning status 253 times consecutively before the status is actually acted on.
It has been suggested that I use the BC548 level shifter on this page, but I fail to see the point:
https://jeelabs.org/book/1504d/The 12V and logic would be swapped to the other direction in this case.