I am planning to try to use a shift register to multiply the input capability for binary inputs on a car dash project I'm developing for a hobby car project. I've got a couple of chips on order to do some bench testing, so while I wait for those I'm trying to figure out what the general circuit design should be. I'm going to run two registers in series to give me a total of 16 inputs via SPI.
I have two types of input coming from the rest of the car. Some switch low to ground, some switch hi with 12v (or whatever the car is currently producing).
I guess I will want to shield the IC from anything on the car side, so my plan would be to use opto-isolators to ensure a complete disconnection of the two sides of the circuit. The only trouble is that 8 of them will take up a fair bit of PCB space but I'm sure worth the trouble.
My understanding of how this would connect to the 74HC165 is as follows for the two configurations, does this look about right? The top one has a 12v input, the bottom one has a switch to ground input.