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rm-hull / luma.core

A component library providing a Pillow-compatible drawing canvas, and other functionality to support drawing primitives and text-rendering capabilities for small displays on the Raspberry Pi and other single board computers.
https://luma-core.readthedocs.io
MIT License
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Question about using SPI bit-banging #138

Closed OnfireNFS closed 6 years ago

OnfireNFS commented 6 years ago

Hi there, I just wanted to know if there is anymore documentation or examples about using bit-banging with SPI devices. I am trying to run 3 SSD1351's off a raspberry Pi 3 simultaneously. I am not too worried about the performance/refresh rate of the displays because they just need to display a clock, some text and the temperature.

Currently I can display the demos to one SPI device at a time (on either SPI0 or SPI1). When I tried displaying the demos on a single display using bit banging the demos no longer showed up and I was having a hard time finding documentation on how to use bit banging.

I was hoping hoping someone could point me towards some documentation or a demo showing how to get my SSD1351 working with bit-banging.

Also, I am aware that the demos only work on one screen at a time. My goal was to get a one display working at a time using bit banging then write a script that could control all 3 at the same time.

Thank you!

rm-hull commented 6 years ago

You shouldn't need to bitbang SPI at all. There are two SPI buses and two chip enable lines, so theoretically you should be able to control upto 4 devices independently.

... Actually, you could just use 3 regular GPIO lines ANDing them to the CE0 line as a crude multiplexer much like in this link: https://forum.arduino.cc/index.php?PHPSESSID=8s0qhkphngmjg9gh791uujooo0&topic=461410.msg3170149#msg3170149

image

The library supports the concept of multiple screens, and I (and others) have had success using multiple SSD1306 screens over I2C using a multiplexer - see https://github.com/rm-hull/luma.core/issues/55.

https://github.com/rm-hull/luma.examples/issues/78 may also be relevant too.

OnfireNFS commented 6 years ago

Thanks I'll give that a try. My end goal is to have 6 SSD1351's working off the same Pi but I was going to start with 3 as a proof of concept. I don't have any multiplexer chips right now so I will have to go grab one. It looks like I should be able to use a 74HC4051 for up to 8 outputs so I think it'll work.

Thanks again for the help!