PC - Passive circuit interface

Hi All - I need some help/advice.
I'd like to connect a magnetic sensor (bicycle computer) directly to my computer through one of the ports without a power supply.

I found the attached circuit but don't know how to test it.

Can anyone make suggestions about circuit design - can I feed the wires directly into my parallel/serial port?

I'm also trying to write a program in VB6 to read the input, but not having much luck.

I'd really appreciate any help anyone could give me.
Thanks
Pete

Yes you can connect these signals directly to a serial port, as long as these are the only connections to the switches.

You'll have to get the spec for a 9-pin serial port, since 25-pin serial ports have been rare since about 1989. Map the signal names on the diagram to the signal names on the 9-pin version.