Some of you may have been reading the thread here where we have been hashing ideas about Optical and Magnetic VSS signals in a powertrain swap. In this thread there were several Ideas on how to feed an optical signal into the magnetic VSS inputs. After testing how the magnetic sensor inputs behave on a 1227727 with a signal generator, I found that the VSS high signal has to swing above and below the ground reference for the ECM to read the signal. I also found that the VSS Low pin is tied to ground with a low resistance. What is needed is a level shifting circuit. I put together a MAX232 circuit which is usually used to convert RS232 signals to TTL. The MAX232 can take a 0-5V signal and output a + and - voltage based on high or low state of the input to one of its transmitter pins. On this test circuit, I used a signal generator to simulate a 0 - 12v input from a signal generator and the zener diode circuit on the input clamps the voltage feeding the chip to 5v before entering the MAX232. I tested this circuit with a 1227727 running the $8D mask and it seems to operate correctly. I have also made a pulse divider circuit for the 0-5v optical VSS sensors. I can divide the signals by 2 or 4. It can take an 8000 PPM signal and output 4000 PPM or 2000 PPM. I will get the circuit drawn up and will post it in this thread. Questions / comments welcome.

Brian