For many years, we sold an adapter to allow old home-made photogates and many other odd digital signals to be sent into a LabPro, LabQuest, LabQuest Mini, LabQuest Stream, or LabQuest 2. Unfortunately we no longer make these adapters. The schematic is available if you would like to make your own.

http://www2.vernier.com/til/3360/hmp-btd.pdf

If you have other old photogates around, and you have a CBL-2P adapter, this could be a good starting point for making your own HMP-BTD. We used to build the HMP-BTD by starting with the circuit board for the CBL-2P or the Dual-Photogate adapter for original CBL.