This exercise began because I wanted to see how far I could go with computer control of a camera particularly in high speed photography.
What has evolved is a stand-alone wireless controlled electronic shutter release.
It is based upon using wireless doorbell units. These can be quite cheap as they are coming in from China. And I was lucky enough to find one that was readily adaptable. Any of them can probably be used so long as you can find where the point on the board is that lets you tap off the signal you need.
The doorbell units I found also make it easier to have multiple receivers controlled by one transmitter. The encoding of a unit simple requires removing existing links and putting in the ones you need.
An overall schematic for the system shows how simple it is: