thinkyhead
commented
6 years ago One piece of code that uses i2c directly is the digipot_mcp4451.cpp file, so that's a good place to start for guidance on implementing a self-contained new feature that uses i2c.
Marlin includes an i2c bus under the EXPERIMENTAL_I2CBUS feature, and this has been used for some real-world implementations. However, none of the features in Marlin uses the TWIBus class, so examples are hard to come by. However, there is this branch which implements a remote Z axis over i2c connected to a second board running a Z-axis only version of Marlin. The implementation details are explained in this thread.
For most cases there's no need to implement a protocol, as in the above examples. The device will already have its address, commands, and replies specified, so you'll only need to poll it periodically.
I2C temperature sensing
Marlin does ADC conversion using a timer interrupt, but the temperature readings are picked up and used within the program loop. So, using i2c means the ADC parts can be dropped, saving cycles, and manage_heaters can just do an i2c request.
I2C Fan control
Pretty simple. Marlin doesn't yet encompass the concept of a fan type. They are currently all assumed to be PWM. The stepper interrupt that moves the stepper motors also changes the fan speed. That logic would remain the same, but the new value would be written to a global (for example, i2c_fan_speed[0]). The main loop would watch for the variable change and do an i2c send to update the fan speed.
Hall effect filament movement and diameter sensor
The Prusa MK3 uses frickin' lasers! Marlin has support for a filament width sensor using an analog pin, and thus ADC. If the sensor is implemented over i2c it saves a lot of computation, even polling 20 times per second.
I2C LED Control to indicate heating status
Heating status is displayed automatically in Marlin if you have one of the color LED options enabled, plus PRINTER_EVENT_LEDS. For a single RGBW LED or multiple LEDs using the same color, these are the current options:
RGB_LED/RGBW_LED- 3 or 4 direct PWM / digital pins.BLINKM- A simple i2c-controlled LED. Seeblinkm.cpp.PCA9632- More complex i2c LED. Seepca9632.cpp.NEOPIXEL_RGBW_LED- Adafruit Neopixel, using their library.
I2C Extruder motor multiplexer (True mixing ?)
E motors need to be well-synchronized with the XY motors, so a multiplexer has some limitations. The Prusa multi-extruder system can't do mixing, so it only needs to route stepper signals to one stepper at a time. A multiplexer that included the ability to mix would need a means to set the mixing ratio, and then on-board Bresenham logic to detect input steps, increment and reset counters, and proportionally redistribute steps. Note that from Marlin's perspective there's only one E axis.
These are some initial notes on your needs. When someone has the time to work on this, do you have all your hardware components already well-specified? Do you know the i2c addresses and do you have datasheets on how to communicate with these devices? Any guidance you can provide in advance will help to prime the gears.
madhunm
bobc
Grogyan
Feature Request
Hello,
My team and I would like to have support for a 'toolhead' we are developing. Its primary features are:
The total number wires that will run from the controller board to the extruder head will be:
We would be bringing the STEP and DIR for the extruder motor channel to the extruder controller board... An I2C processor will turn those two signals into several physical stepper motors...
We would like to understand how the feature request works; we dont mind attaching a reward for the same.
The entire project will be OSHW.
Thanks!