Optically isolated 24v analogue input

[SteveSFX]

Hello world of people cleverer than I am

I am designing a project board where I can control various 'things' from inputs. outputs etc. optically isolating my inputs and outputs with 6N137's.
But, I also have 6x analogue inputs. Not sure what voltage they will be covering/reading yet, but probably up to 24v.

I have been reading up on opto-isolators for analogue signals, and it doesn't seem simple. Apparently the thinking is to use something like a LOC111 with 2x internal receivers, so that one can try and compensate for the non linear response.

My thought... rightly or wrongly was to maybe control a voltage to frequency circuit with the incoming signal, and read pulse that optically? Maybe go super simple by using a 555 or something.
Doesn't need super speed, so the pulses can be quite 'lazy'.

Just wondered if anyone had any thought or ideas

 

[SteveSFX]

If i may ask... how do you guys access the pins under the 3.2 when designing a pcb? I Almost wish the 3.2 board was a little larger and all the pins on the same side.
I was thinking of through hole pads that line up with the middle pins underneath, then heavily pre-tin the middle pads before installing it.
Then, push fine wire/pins through the pcb from the front and solder.. hopefully they will attach to the solder on the 3.2. Not easy to check for a good connection however.

I am considering binning those pins and adding an MCP23017 (16 pin I/O chip using I2c), and using that instead for a further 16 pins. Just seems a shame to waste perfectly good direct connections.