I have read a few threads on the site in regards to VSS. I would like to generate a signal for my car stereo VSS input, to allow directions to be added by the passenger Via blue-tooth. In order to do so I believe i need to create a square sign wave with a voltage of around 5v. I have a NE555 pulse modulator and a LM2596 adjustable power supply. I'm still investigating what frequency to generate but it looks like the NE555 will be quite capable. What is the best way to measure the frequency output from the NE555. Any thoughts would be appreciated.