Pretty sad information you're feeding these people. All vehicles have a VSS wire that transmits a Digital DC signal...
Whether it be a wheel speed sensor, cam/crank sensor, VSS on the trans it consists of:
A reluctor (toothed wheel)
Magnetic Pickup
Coil of wire
They're all digital...
As for ANALOG signals (TPS, MAP, MAF) most of them need to be converted to Digital DC so the PCM can understand the signal.