MAX7219 Part Request

[rcwilcox]

Would it be possible to add the MAX7219 Seven Segment Decoder? I would like to use this to prototype/simulate projects for STEM education using Multiplexed Seven Segment LEDs.

Note: Clarification due to @sutabutosu question below - This a request for a standalone MAX7219, not an integrated MAX7219 and 7 Segment Display.

MAX7219 Datasheet

[sutaburosu]

@rcwilcox if you have an 8-digit 7-segment display with a MAX7219, could you please check which order the digits are wired? To my mind, it would make most sense for digit 0 to be on the right, increasing to digit 7 on the left. It would be nice to confirm this on real-world hardware.

[rcwilcox]

@sutaburosu I haven't prototyped this with real-world H/W since I don't have the H/W. I 'simulated' the interface (Address/Data) on Wokwi with two 74HC595 Shift registers chained together over SPI and used Digit 0 (labeled sevseg:DIG4 on a 4 segment wokwi-7segment part) on the right. Of course I had to do the hex->segment decode in S/W for this to work. This indeed makes the most sense.

[sutaburosu]

I found this datasheet for an 8-digit display. It's still not entirely clear to me which end is digit 0. The only hint I can find is at the bottom of page 9 where they mention blanking leading 0s using the scan-limit register. This tends to suggest digit 0 is on the right.

[rcwilcox]

Wouldn't it depend on your implementation of the display with the 7219? To be clear, I am looking for the 7219 part alone, not 7 segment LED(s) integrated with a 7219 (which seems to be what the 7219-LED matrix is). You would use it as a decoder between the serial interface and the standard 7 segment display.

[sutaburosu]

Oh! I was imagining a part similar to the existing MAX7219 64 LED matrix, but with a configurable number of 7-segment digits. I can see that a MAX7219 is a useful component in its own right, if you're keen to show the wiring.

[rcwilcox]

This is how I simulated it

[rcwilcox]

Timing diagram

Note: This data is sent repeatedly over SPI and ISR attached to a timer. The MAX7219 Part would only require a single load and updates when display changes are required, the 7219 would handle the scanning duties along with decoding.

[rcwilcox]

Here is the API. Note that I had to pre-decode the Addr and Data in the AVR software to set the DIGn Enable (Address) and 7 Segment Data. The MAX7219 part would simulate this decoding per the datasheet.

[urish]

Closing this issue as it hasn't received any votes in 6 months. Note that this could now also be implemented as a custom chip (see #301)