
All you need is 4 caps, one IC and 2 connectors. If you want to add a small regulator on the board (already foreseen on the PCB) you just need to add a 78L05 regulator and a cap.
If you do not need to regulate the power supply, you can just replace the 78L05 by a strap (pin1 to pin 3) and drop the 78L05, C1 and C2.
Schematic

PCB

Component Layout

Component List
C3-C4-C5-C6 : 10uF 16V
IC1 : MAX232
C1 : 100uF 25v (If regulated power supply needed)
IC2 : 78L05 (If regulated power supply needed)
C2 : 100nf (If regulated power supply needed)
DB9 Female
Connector
All Files and Prints
contributed by Olivier de Broqueville.