The MegaSquirt Project has experienced explosive growth other the years, with hundreds of new MS installations occurring every week - a phenomenal success! MegaSquirt has been successfully used in all aspects of Internal Combustion engine applications including R&D, Industry, Race, and Research. The MS project has transformed itself from a simple R&D project into a full-featured mature engine control system. To reflect this the support structure has also changed to meet the needs of MegaSquirt Users.
Moving forward, the R&D forums for MegaSquirt project are in a read-only mode - no new forum posts are accepted.
However the forums will remain available for view, they still contain a wealth of information on how MegaSquirt works, how it is installed and used. Feel free to search the forums for information, facts, and overview.While the R&D forum traffic has slowed in recent years, this is not at all a reflection of Megasquirt users, which continue to grow year after year. What has changed is that the method of MegaSquirt support today has rapidly moved to Facebook, this is where the vast majority of interaction is happening now. For those not on Facebook the msextra forums is another place for product support. Finally, for product selection assistance, all of the MegaSquirt vendors are there to help you select a system, along with all of the required pieces to make it complete.
A forum for discussing applications and implementations of the MegaShift transmission controller code for the GPIO from B&G. This can control up to 8-speeds and 6 shift solenoids (plus a 16x9 table for controlling a PWM line pressure valve). It has manual and fully automatic modes (16x9 load x speed table), with under and over rev-limit protection, and full data logging of all inputs and outputs (among many other abilities). A TransStim to test your completed board is also available.
I believe, depending get on your trans, when at full pressure solenoid is off. As you lower the pressure the valve is on more.... and regardless of pulsewidth as duty increases valve will get hot. Think of pw as hz. If you have a long pw it might go back and forth 10 times at 100%DC. If you have a short pw it could go back and forth 50 times at 100%DC. Either way valve is constantly on at 100%DC. And duty cycle is the time on so as you drop pressure duty increases. So the resistor helps with overheating. I run mine full pressure and the resistor stays cool so it's not working much, only during shifts do I drop pressure
I did some SPICE modeling of the solenoid, the resistor a diode and a switch (BJT). With the flywheel diode, the current through the solenoid doesn't stop quickly enough to provide a linear average current across the range of duty cycles. That is, it's no longer PWM because the current rise time through solenoid is much faster than the fall time. If we remove the resistor and the diode and replace the transistor with a 60Volt internally clamped low side switch, it works and the low side switch power dissipation is 60W peak but only about 3W average.