Serial Cable for Casio Digital Cameras

I built this cable for my Casio QV-200 digital camera, it should work for many Casio models. It's basically a inverting buffer/converter to/from RS-232 voltage levels from/to CMOS levels. Why Casio didn't put this inside the camera like everyone else does is beyond me. I built the circuit inside the hood of the DB9F connector.

Schematic Diagram:
Download it or look at it.

Parts List
Micro 3/32 inch stereo phone plug(Radio Shack 274-298)
DB9F plug
PN2222 or generic NPN transistor
PN2907 or generic PNP transistor
1N750 or generic 4.7 volt zener diode (1N751 5.1 volt allowable)
1N4148 or generic diode
220 ohm resistor
4.7 Kohm resistor
10 Kohm resistor(quantity 2)
3 feet of cable, preferably 2 conductors plus shield

If you have all the parts except the Zener diode, you can substitute three red light-emitting diodes. They must be RED because the voltage drop is different for different color LEDs. This picture shows the connection: