SimHubPWMfans

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Blue Pill PWM fans for SimHub

updated 7 Mar 2023

Name	Size	Date Modified
PWMfans.shsds	3.3 kB	9/30/21, 8:09:14 PM
SimHubPWMfans.ino	1.8 kB	9/30/21, 7:51:17 PM

Warning! 7000 RPM 280CFM fans run full speed without PWM connected
and must be anchored!
The Blue Pill module in that image was destroyed by a runaway fan...

Background

An STM32duino sketch was hacked to control 4-wire PC fan speeds.
Unlike (50Hz) hobby servos, 4-wire PC fans want 25kHz PWM...

SimHub Custom Serial sends (7-bit) ASCII with (6-bit) fan speed values

One bit is allocated to selecting left vs right fan.
A SimHub ShakeIt Bass Shakers SPEED WITH CURVING effect will generate SpeedCurv properites:

A fan speeds profile will be hacked from a SimHub Custom serial device for harness tensioning:

• while a single Blue Pill can easily support both hobby servos and PWM fans,
  appreciable physical separation make separate Blue Pills less hassle.
• SimHub Custom serial plugin supports multiple devices at different COM IDs.
• A JavaScript message will convert left+right SpeedCurve properties to 7-bit speed values.
• An Arduino sketch will scale those to (25kHz) PWM fan control values.
  An STM32 Blue Pill is capable of driving at least 7 PWM devices,
  using available 5V-tolerant pins PA8-10 and PB6-9.
• Timer 4 for PB6-9 is already configured for hobby servos.
• Timer 1 channels 1-3 control pins PA8-10.

While a Black pill (STM32F401/F411) module could also be used,
it would be overkill, and Arduino support is less well documented.

sierses used sgbotic instructions for Black Pill with Arduino

"The only change I had to make was using SWD for the upload method. STM32duino supports the f411 now."
"it took a few tries before I got it working. After I flash it the first time,
the serial connection initializes through the USB port, then I can flash it again
and it will automatically reinitialize and SimHub will reconnect,
so the button dance only needs to happen once when it's first connected."

further stm32duino PWM hints

When servo.attach() is called on a certain pin, the hardware timer responsible for creating the PWM signal is set to a certain period/frequency. On the Blue Pill, this period/frequency is synchronized across all pins that the timer is responsible for. So if you have a motor running on the same timer as a servo but another motor running on a different motor, the motor speeds will differ because their PWM frequencies will differ.

Synchronizing all timers:

void timerSetup() {
    for (int i = 1; i <= 4; i++) {
        HardwareTimer timer(i);
        timer.pause();
        timer.setPeriod(20000);
        timer.refresh();
        timer.resume();
    }
}