Implementing Servo Support
My original intent for servo motor support was to use a PCA9685 based i2c controller and provide the implementation as an example that users could expand upon to create a full application.
I intend to still provide support for the PCA9685 in the future but as an installable library. Getting the PCA9685 to work with the existing i2c support should be reasonably simple to get going, so I would see if there is some way to create libraries for device support and have the ability to “optionally install” them at compile time. Creating installable library support will take some thought and experimentation, so I am putting that on the back-burner for the moment.
Instead, I am currently experimenting with providing direct PWM support for servo motors. Servo motors require a frequency of 50 Hz. That is to say, that a pulse is generated every 20 ms, sometimes expressed as a period of 20ms. To vary the servo’s position between 0 and 180 degrees, the pulse is set to between 1ms and 2 ms.
Modifying the code on this Raspberry Pi Forum posting, I generated the 20ms period without writing any PIO code. However, I have not been able to get the resolution for generating the 180 different pulse lengths for servo control. I will be spending a few days on this, but I am not very hopeful for success on this front.
So, what is plan B? I recently read about an Arduino-Core compatible library being released. I am considering reusing the PIO code in the servo library.
If I do so, I will give the original author full attribution, as so richly deserved.
The original intent of the Telemetrix project was to repurpose Arduino-Core libraries to run on the various Telemetrix supported MCU boards. Using a board-specific Arduino-Core makes porting from one board type to another quick and straightforward.
When I started this project, the Arduino-Core was not available, so I decided to use the Pico C-SDK directly. Part of the fun, for me at least, in doing these types of projects is expanding my knowledge, even when it can be slow going and sometimes frustrating. So, why not use the now available Arduino-Core if porting is likely to be quick? The reason is that many of the available Arduino libraries have yet to be ported to the Pico, so if I want to support some additional devices, such as an HC-SRO4 distance sensor, I would have to generate the PIO code anyway. By keeping control over device support, I do not have to contend with libraries that might break future releases.
Because I am treading where I have limited expertise, things may progress at a somewhat slower pace. I ask for patience since I believe it will result in a better overall user experience in the end.
As always, stay tuned.