This is a tiny (Bare PCB dimension: 45mm(W) x 20mm(H)) USB to serial converter using the low cost CH340c chip with a few surrounding parts. The advanctage of CH340c is no external crystal needed that could cut down the cost. The mainly used pin at the tail of the board is compatible with FTDI breakout board, so you can use it to program Arduino Pro mini by temporary touching the pins of the boards...
This circuit is designed to replicate the optical trigger output used on Siemens scanners, and to make a standard TTL pulse available.
The purpose is to allow multiple devices to be daisy chained on the trigger line.