Ideally I'd like to avoid the opamp route as I have the transistors and SCR in my parts bin already. The latching effect of the SCR is also desirable.
This is for a (low power) ballistic chronograph. The LED and PD will be 1-2cm apart, enclosed in a tube. The projectile will be travelling at 300-1000 FPS so the change in output from the PD will be very brief.
The circuit I have referenced is known to work for this use-case. I found it used in a similar project based on NodeMCU rather than Arduino.
I'm asking what other changes (if any) will be required if I want to use a PD rather than PT and looking to confirm the PD should be used in reverse bias - so the cathode connecting to the 2N2222/resistor junction and anode to GND? Based on reading I think the PD is more sensitive and responds more quickly when used this way.