Rant (actual content below)

Outside of electronics nerdery, my other biggest past-time is bike nerdery. Over the years a group of friends have put on various events, a kind of 'bike games'. During one of these back in 2009 or so we did a street version of a classic track cycling event called the Flying 200. It's a 200 meter sprint were the racer can take a 'running' start, starting as far from the start line as they want. As soon as they cross the line, timer starts and end 200 meters later. Our method of timing with stop watches are walkie-talkies was fun, but not exactly precise. Since then I've made a couple version of line break timers but were always plagued by lack of handling of variable lighting conditions. This inspired the #74xx Hamamatsu S6986 project, which has in turn inspired my design to learn analog electronics better.

Actual Content

The design is largely based on the IRis project on Analog Zoo and a more basic design by IMSAI Guy. I've tried breadboarding out a simple in between design but I just don't have the right parts. I only have older opamps and BPW34 PIN diodes that don't seem to want to work. So I'm sticking closer to the IRis part selection in the hope it'll work better. In addition to the detection circuit I'm including the laser diode on the same board.

This is the circuit so far, I still probably need to do more in the driving circuit, I haven't put much though into that yet. But I suspect the detection circuit should be alright as it's pretty close to the IRis.

https://gitlab.com/morganrallen/52-boards/-/tree/development/Transimpeadance%20Amp