VEMS uses the PS2 clock signal to receive 0/5V wheelspeed frequency signal.
Therefore the non-PS2 firmware must be used ( my_make.16x14/vems.hex ). See GenBoard/UnderDevelopment/FirmwareChanges around and after 1.1.53
Sensitive pin
PS2 clock input is a direct CPU pin. It is very sensitive. Either static electricity or 12V will damage the main processor immediately.
Therefore many users request in the WebShop order note:
- PS2 clock wheelspeed input on EC18/17 instead of 2nd WBO2 FET.
- 4k7 pullup to +5V
- 4k7 and 5V1 zener protection on the processor pin
This way it is less likely to damage it, and an open-collector HALL sensor or a VR signal and a simple NPN inverter can be used to drive the signal (LM1815 is not necessary for this, although that would work too). Care is still needed of course.
Wheelspeed data usage
- logging wheelspeed to notebook, or SDcard
- sending to AfreshTiny/AimDisplay for well-visible display
- boostcontrol - gear dependent boost
- launchcontrol - wheelspeed dependent rpm-limit
Launchcontrol
The good old initial launch behaviour with retard and launch-enrichment is still there.
But after reaching the first entry in an 8 entry table (array), no retard, no enrichment:
2x8 bytes for wheelspeed => RPMlimit. Firmware uses interpolation for smooth transitions between table-points.
RPMlimit is in 100 RPM unit.
wheelspeed is the unit of your choice. Usually:
- km/h
- or mph
- or any other. It really just depends on calibration
The same table is time => RPMlimit for the PS2 firmware where wheelspeed is not available. Time is in 64 msec unit.
The first and last bin in the table are somewhat special:
- Before the first entry is reached, the good old one-value RPMlimit set in config is used and retard and enrichment is applied
- after the last bin, launch is disabled and not active any longer.
Note: the "launch-active" flag in VemsTune only lights up when the RPM-limit is reached (not when the button is pressed - this can be confusing). So if you want to test an analog input switchbutton, configure the ALS input to that pin to see that it lights up.
REST OF THE PAGE IS BRAINSTORMING
Freq to voltage - could also be used
[LM2917] frequency to voltage converter to get wheelspeed info on the LCD and for logging.
The app note even has a design almost ready for use
Is anyone besides me interested in this?
Is there any problem with this solution that I am missing? //Emil