Serial header to db9?

[dsweet]

Is it possible to connect the geiger counter's serial port directly to a PC's db9 serial connection? I connected the pinouts (minus the vcc) and only getting gobbly-gook.

[mightyohm]

No, the voltage levels are not compatible.

You need to use a level converter like the MAX3221 to convert the 3V TTL levels from the geiger counter to the RS-232 levels that your PC needs.
http://www.maxim-ic.com/datasheet/index.mvp/id/1069

Edit: Or a USB-serial cable like the FTDI TTL-232R-3V3: http://www.ftdichip.com/Products/Cables ... Serial.htm