Node.JS program to read 'clicks' from a GM-10 Geiger Counter by BlackCat Systems
http://www.blackcatsystems.com/GM/GeigerCounters.html
I would think it should work with the GM-45 and GM-90 models as well, but I don't have those, so I don't know for sure.
This program reads the 'clicks' generated by an GM-10 connected to a computer serial or USB port, and then reports out using the MQTT protocol the number of Clicks Per Minute, or CPM. You can convert CPM into 'Rads' or 'Sieverts' for a more normal unit of measure. BlackCat Systems has a very good page describing how to do this conversion (http://www.blackcatsystems.com/GM/converting_CPM_mRhr.html).
You will want to modify the Constants part at the top of the program to work with your systems.