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BRUH Automation

7-Segment Display

Eight red digits in a printed wedge on the desk, showing one number out of Home Assistant. The config points at sensor.youtube_subscribers, which is what it was built for, and that one line is the only thing tying it to YouTube — point it at solar export, watts on the main panel, degrees outside, days until a thing. The value is pushed to the ESP32 over the ESPHome native API, so there is no MQTT broker, nothing polling, and no dashboard involved.

It is a small build. One board, one display module, five jumper wires and two printed parts, and the whole thing runs off a phone charger.

Parts

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  • ESP32 dev board (ESP-WROOM-32, 38-pin narrow) — a 2-pack. The config’s board: nodemcu-32s is a generic WROOM-32 key and every pin in the file is addressed by GPIO number, so any WROOM-32 devkit works. Read the hatch note under Assembly before you print the case
  • MAX7219 8-digit 7-segment display module — a 2-pack, you need one. num_chips: 1 in the config means exactly one of these
  • Dupont jumper assortment — 20 cm wires in all three genders. The five you want are the female-to-female ones, module header straight onto the ESP32’s
  • Right-angle 1 ft micro-USB cable — a 3-pack. The port is a slot in the end wall of a case only 28 mm deep, so a straight plug stands further off the back than the wedge is deep
  • 2.4 A USB wall charger — 3-pack. Eight digits at mid brightness draw very little, but don’t run it off a 500 mA charger
  • Black PLA+ — 4 × 1 kg. Black matters here: it is the bezel the red digits read against
  • 3M VHB 5952 tape, 1/2 in — two short strips hold the display module against the back of the window. Thick CA glue works too if you are confident about placement

Three STLs ship, and only two of them are print files. esp32_7_seg_v3.stl is body and lid assembled — the thing you spin in the viewer at the bottom of this page, not something you slice. What you print is esp32_7seg_body.stl and esp32_7seg_back.stl.

The body is 87 mm wide, 28 mm front-to-back and 22 mm tall, with a 63 × 16 mm window in a face raked back 43° off the desk. The lid is a 22 × 25.5 mm plate 2 mm thick, with a 20 × 21.5 mm plug that fills the hatch.

SettingValue
Layer height0.2 mm
Perimeters2
Infill15%
SupportsNone
MaterialPLA
OrientationBody base down, the 87 × 28 face on the bed; lid flat

The shell is 1 mm thick, which two perimeters fill on a 0.4 mm nozzle. There is almost nothing left inside for infill to reach, so set the density and stop thinking about it.

Base down, every outside surface faces up or sideways. The window face is a top surface at 43°, and the top edge of the window closes over at that same rake rather than bridging. The one overhang in the print is the cavity’s own roof — the underside of that same face, at 47° from vertical — and it goes up without help. If your slicer wants to support it, turn supports off rather than let it pack the case with material you then have to fish back out through a 20 mm hatch.

Wiring

Five wires. Every pin below comes from the ESPHome config in the folder.

MAX7219 moduleESP32Config key
VCCVIN / 5V—
GNDGND—
DINGPIO22spi: → mosi_pin
CSGPIO23display: → cs_pin
CLKGPIO21spi: → clk_pin

GPIO21 and GPIO22 are the ESP32’s default I²C pins. The GPIO matrix does not care and SPI works there fine — just don’t reflexively hang an I²C sensor off this board later without moving one of them first.

The MAX7219 is a 5 V part and the ESP32’s logic is 3.3 V, so the three signal lines are technically under spec. Most modules do not care. If yours lights up as garbage, or not at all, move VCC from VIN to the 3V3 pin — the chip runs below spec quite happily and the only cost is a little brightness — or put a level shifter in DIN, CS and CLK.

There is also a status_led on GPIO2, which is the blue LED already on the board. It is useful while you are bringing the thing up on the bench and invisible the moment the case is closed.

Assembly

The shell has two openings. A 20 × 22 mm hatch in the base at one end, which everything is installed through, lengthwise, into an 85 mm cavity; and a 10 × 4 mm slot in the far end wall, sitting on the cavity floor, which the USB lead comes out of.

The hatch will not pass the ESP32. Check this before you print. The cavity is 26 mm across, a slip fit on a 38-pin devkit lying flat — but the hatch into it is 20 × 22 mm and the board is about 25 mm wide. The display module goes through; the board does not. Open the hatch out in cad/esp32_7_seg_v3.f3d, or the STEP beside it, before you slice — otherwise you print a closed box you cannot get the electronics into.

  1. Print the body and the lid, and dry-fit them empty. The lid’s flange sits on the inside of the base, so it goes in at an angle and is then pulled back down into the hatch; it is not a plate that drops on from outside. Find that out now, not with a wired display already glued in.

  2. Wire the five leads and flash the board first, on the bench, with the case nowhere near it. Nothing in here is reachable once it is assembled, and a display that shows the right number on the bench is a display you only have to mount once.

  3. Feed the display module in through the hatch, digits facing the window, and line it up with the opening — the window starts 12 mm in from the hatch end and runs 63 mm, so the module sits across the middle of the case rather than against either wall.

  4. Hold it against the back of the window with a short strip of VHB along each long edge of the PCB. Keep adhesive off the digit faces — a smear of glue on a segment is permanent and shows in every photo you take afterwards.

  5. Put the ESP32 in below it, USB port toward the far end — away from the hatch, so the socket lines up with the slot in the end wall. Dress the five jumpers so nothing presses on the plug.

  6. Work the lid in and press the plug home.

The end slot is cut to clear the socket on a devkit and not much more. If the moulding on your cable is too fat to reach through 10 × 4 mm, a few strokes with a flat file opens it up — do it before the board goes in, so the swarf falls out of an empty case.

Configuration

The config is esphome/bruh-7-segment-display.yaml, in the download section below.

  1. Change the two substitutions at the top so the device gets its own name:

    substitutions:
      device_name: "Desk Display"
      device_id: "desk-display"

  2. Fill in secrets.yaml — this config uses wifi_ssid, wifi_password and ota_password.

  3. Point it at the number you actually want. This is the block that matters:

    sensor:
      - platform: homeassistant
        name: "Subscribers"
        entity_id: sensor.youtube_subscribers
        id: subscribers

    platform: homeassistant means Home Assistant pushes the value down over the native API. The entity has to exist and has to be numeric. Swap the entity_id for yours and leave the id alone, because the lambda refers to it.

  4. Flash over USB the first time. Everything after that goes over WiFi.

The device is discovered by the ESPHome integration on its own — there is nothing to add on the Home Assistant side.

Things worth changing

Right-align the number. The lambda prints at position 0, so a four-digit value sits on the left of an eight-digit display with four blanks trailing it. Pad it:

lambda: |-
  it.printf(0, "%8.0f", id(subscribers).state);

Handle the entity going unavailable. An unavailable Home Assistant entity arrives as nan, and %.0f renders that as literal garbage across the digits. Guard it:

lambda: |-
  if (isnan(id(subscribers).state)) {
    it.print(0, "  ----  ");
  } else {
    it.printf(0, "%8.0f", id(subscribers).state);
  }

Brightness is intensity, 0 to 15. The config ships at 8, which is right for a lit room and too much at 2 a.m. If it sits in a bedroom, drive it from an automation instead of hard-coding it.

Make it a clock instead. There is an SNTP time: block in the config with the id sntp_time that nothing currently uses — it is in there so you can do this:

lambda: |-
  it.strftime(0, "%H.%M.%S", id(sntp_time).now());

The dots between the fields are the display’s decimal points, which is what those otherwise-useless dots on a seven-segment tube are good for. A clock takes six of the eight digits.

Troubleshooting

Nothing lights up at all. Check VCC before anything else — the module needs power from VIN, not from a 3V3 pin you grabbed because it was closer. Then check CS on GPIO23. Swap CS and CLK and the chip never latches anything at all, so you get a dead display rather than junk on it, which reads exactly like a dead module.

Digits show, but they are nonsense. That is the 3.3 V logic level. Move the module’s VCC to 3V3 and try again.

The number reads backwards. Some MAX7219 boards wire their digit order the other way round. It is a property of the board you bought, not of your wiring: try reverse_enable: true in the display: block first, and if that doesn’t flip it, build the string in the lambda and reverse it there.

It shows nan or a row of dashes. The Home Assistant entity is unavailable or isn’t a number. Check it in Developer Tools → States; a sensor whose state is unknown or a string will do this every time.

It never appears in Home Assistant. The api: block has no encryption key in this config, so it relies on the ESPHome integration finding it by mDNS. If your network drops multicast between VLANs, add the device by IP address manually.

Files & downloads

Printable parts

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Parts marked from CAD are tessellated from the STEP files below, for previewing only — approximate where the STEP is exact. Download the STEP for the real model.

ESPHome configuration

Copy this into your ESPHome directory and adjust the substitutions at the top. Secrets are referenced by name — see secrets.yaml.example .

bruh-7-segment-display.yaml 69 lines
bruh-7-segment-display.yaml
# BRUH 7-Segment Display
# ────────────────────────────────────────────────────────────
# MAX7219-based 7-segment display showing data from
# Home Assistant (e.g., YouTube subscriber count).
#
# Hardware:
#   - Board: ESP32
#   - Display: MAX7219 8-digit 7-segment
# ────────────────────────────────────────────────────────────


substitutions:
  device_name: "BRUH 7 Segment"
  device_id: "bruh-7-seg"


esphome:
  name: ${device_id}


esp32:
  board: nodemcu-32s


wifi:
  ssid: !secret wifi_ssid
  password: !secret wifi_password


ota:
  password: !secret ota_password
  platform: esphome


api:


status_led:
  pin:
    number: GPIO2


logger:


sensor:
  - platform: homeassistant
    name: "Subscribers"
    entity_id: sensor.youtube_subscribers
    id: subscribers


  - platform: wifi_signal
    name: "${device_name} WiFi Signal"
    update_interval: 300s


binary_sensor:
  - platform: status
    name: "${device_name} Status"


switch:
  - platform: restart
    name: "${device_name} Restart"


spi:
  clk_pin: GPIO21
  mosi_pin: GPIO22


display:
  - platform: max7219
    cs_pin: GPIO23
    intensity: 8
    num_chips: 1
    lambda: |-
      it.printf(0, "%.0f", id(subscribers).state);


time:
  - platform: sntp
    id: sntp_time

View on GitHub · Download raw

CAD source

The design itself, if you want to change it rather than print it. A STEP file is exact geometry and opens in almost anything; a Fusion 360 archive keeps the modelling history, so you can go back and edit the sketch that made the part.

Every file for this project on GitHub →