Interesting,

If I need to split hairs (volts) I do not like to rely on TTL or ST for the threshold. I set up an ADC.
Well I've never done ADC, it does look an ideal application for the project and new learning for me.

When you have some spare time (spare time, as rare as hen's teeth he says) could we do some ADC stuff? No rush, as and when, as ever.

Dave