MAX7219 doesn't initialize properly at power-on

ESPHome
1

Hi,
I have a Wemos D1 driving three MAX7219 7-segment displays on separate CS lines from the Wemos. The displays show three values from Home Assistant (2023.1.5) related to electricity price and consumption

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All works well except for the first boot after power-cycle when the displays stay blank. Checking Home Assistant I see the D1 connects and values are sent. The display_brightness is restored to the previous setting as well. Rebooting the device either through the RESET button or through a restart_button brings the display back to life.

I now have an automation in HA waiting for the device to power on and connect, then call button.press service on the device’s reset button.

Can I to do anything else to get the displays to work at boot without the work-around?

/Mattias

button:
  - platform: restart
    name: "Restart"

spi:
  clk_pin: D0
  mosi_pin: D5

number:
  - platform: template
    id: max7219_bright
    name: "Display brightness"
    optimistic: true
    restore_value: True
    initial_value: 5
    step: 1
    min_value: 1
    max_value: 15

display:
  - platform: max7219
    cs_pin: D6
    num_chips: 1
    lambda: |-
      it.printf("Pr%7.2f", id(cost).state);
      it.set_intensity(id(max7219_bright).state);
  - platform: max7219
    cs_pin: D7
    num_chips: 1
    lambda: |-    
      it.printf("En%7.2f", id(energy).state);
      it.set_intensity(id(max7219_bright).state);
  - platform: max7219
    cs_pin: D2
    num_chips: 1
    lambda: |-
      it.printf("Sun%6.2f", id(prod).state);
      it.set_intensity(id(max7219_bright).state);


sensor:
  - platform: homeassistant
    name: "cost"
    id: cost
    entity_id: sensor.energy_huset_cost
  - platform: homeassistant
    name: "energy"
    id: energy
    entity_id: sensor.energy_huset
  - platform: homeassistant
    name: "Prod"
    id: prod
    entity_id: sensor.solaredge_energy_today_kwh
1 Like
2

Anything interesting in the Verbose logs? They might be hard to catch after a power cycle I guess…

I wonder if it could be a power issue? Maybe on power cycle there is a power demand spike and not enough for proper set-up of your displays? I heard capacitors can be charging etc.

Does it happen if you just have one display connected with minimal brightness and a good quality power supply?

If you are daisy chaining them maybe the voltage drop is too high?

From docs

You can even daisy-chain multiple MAX7219s by connecting the DOUT of the previous chip in the chain to the next DIN. With more than ~3 chips the 3.3V will probably not be enough, so then you will have to potentially use a logic level converted.

Are you powering them from 3v3? Tried 5v?

3

Thanks for the feedback!
Power supply was the issue for some reason (it’s been working on 3.3V from the D1 since this summer). I connected the displays (MAX7219 LED module 8 Bit 7 segment display LED display for Raspberry Pi – AZ-Delivery) to 5V instead and now all works.