Op-amp voltage on output during connection to constant current source
To interface into your GDO to make it remote controlled your spec identifies a 10mA current source and exclusive switch operations with a series R of 82.5Ω, the other is 203.5Ω.
This is equivalent to sinking a voltage of 825mV or 2035 mV.
I propose you can achieve this with two NPN transistors, two diodes, one silicon (0.65V) one Red LED (2V) and a base resistor for each in the 20K range to tweak Vce.
Proof of concept.. Tolerance error &lt; 100 mV