I’m designing a circuit that uses an ESP32-S3-DevKit1 to drive a MAX2719/7221 and 1088AS, just as I promised in the last post. The broad steps are:

1. Write software to communicate with the MAX7219 and 1088AS,
2. Write software that enables Bluetooth on the ESP32-S3,
3. Write software on both the ESP32-S3 and Raspberry Pi 5 to communicate status and messages to display on the 1088AS.

In order to create the schematic diagram in KiCad I had to import symbols for the Espressif components. There’s a link at the bottom that leads to Espressif’s GitHub repo, complete with instructions on how import those symbols into KiCad 7. The Espressif instructions are short, sweet, clear, and they work without exception.

I’m also reading Espressif’s documentation on how to work with the ESP32-S3’s SPI port.

Links

• Espressif KiCad Libraries — https://github.com/espressif/kicad-libraries
• SPI Master Driver — https://docs.espressif.com/projects/esp-idf/en/latest/esp32s3/api-reference/peripherals/spi_master.html

This is the exact same schematic as used in the last post. The big difference is that Inkscape exported the KiCad SVG drawing at 600 DPI instead of 300 DPI. As a consequence, if you zoom in on US, the 1088AS component, the internal LEDs and wiring is a lot clearer. The original 300 DPI export follows.

I’ve set Inkscape’s default export to 600 DPI. Inkscape appears to have a command line capability, which means that I might be able to kick off the export from SVG to PNG within KiCad itself. I need to do more research on that.

It bothered me quite a bit that my last few schematic diagrams were missing the 8×8 LED matrix display. As it turns out, the part number for the 8×8 LED display is printed on the side: 1088AC. When I went looking for any part sheets for it, all I found was a single page with this printed on it

It was a PDF with a copy of a copy of the circuit diagram. I could barely make out the column, row, and physical pin numbers. I then went looking for an open source KiCad part for the 1088AC and found one on GitHub, which I forked and then cloned from my fork. I was able to quickly ascertain that the part was designed for KiCad 6. From there I used KiCad’s part library manager to import the part and then convert to KiCad 7 format. I had to do a bit more work with it before I could use it. For example, all the LED symbols were reversed, pointing up (as common anode) instead of down (common cathode). A little work to select and flip each diode symbol took care of that. I also change all the row pins from input to output, as they were all defined as input.

I am aiming to order a dozen or so MAX7221 parts from e-bay. The MAX7221 has a few additions internally over the MAX7219, one of which is that it support QSPI format data communications. Same price as the MAX2719, same pinout.

What’s interesting about the MAX7219/MAX7221 part sheet, it mentioned on the front page that it was suitable for LED matrix displays, but all the circuit diagram examples only show seven-segment by eight character displays, such as the one on the right above.

More learned with KiCad 7; better control with the schematic diagram, the ability to import parts, and the ability to convert from KiCad 6 to KiCad 7. When I’m finished with the 1088AC KiCad drawing part I’ll update my GitHub version and post a link to it in another post.

Links

My copy with updates and migration to KiCad 7. Note that only the 1088AS part has been updated. — https://github.com/wbeebe/kicad-LED_DotMatrix