Make a TTL Trigger using Arduino. Simply writing a 5V voltage to one of the digital pins should do the job.
This version outputs the ttl signal to a BNC terminal commonly used in scientific instruments. The sketch also includes an option to define duration for which the TTL trigger will be on HIGH.
Assemble the circuit according to the following schematics:
The rep also includes a mount which can be 3d printed for encasing all the components. The mount is compatible with a Nano mounted on breadboard, and has slots for LED and push button.
Get the components and complete the electric circuit. You can bypass the voltage regulator, in case the signal is too weak.