Lights from the glass

Two Zigbee lights switched — and one of them dimmed — from the touch glass of an STM32F746 Discovery, through Home Assistant. The board never speaks Zigbee: its switches and its slider are ordinary ctrl32 variables, MQTT discovery turns them into HA entities, and four small HA automations bind those to the real lights.

The project is installed with the editor in tutorials\. The broker route is the same as every HA connection — Home Assistant covers it; the EVB thermostat tutorial is this page's sibling, with the data flowing the other way.

---

The design decision worth copying

Every card carries two truths: the switch is what you ask, the lamp beside it is what Home Assistant reports back from the real bulb. They are different variables on purpose (light1_on vs fb1_on) — a drive gets the same treatment (controlword vs statusword), and lights deserve no less. Turn the bulb off from a phone and the lamp on the glass goes dark, while the switch still shows what was last asked; the "any light on" lamp in the header sums the ACTUAL states, not the wishes.

---

What you create, step by step

1. Project and board

New project, board ST 32F746GDISCOVERY, 480×272. Ethernet with DHCP runs by itself.

2. The variables

3. MQTT

mqtt:
  broker: 192.168.0.53
  username: ctrl32
  password: ctrl32mqtt
  client_id: ctrl32-f7lights
  topic: ctrl32/f7lights
  publish_mode: per_tag
  discovery: true
  interval_ms: 1000
  tags:
    - { name: light1_on,  write: true }
    - { name: light1_dim, write: true }
    - { name: light2_on,  write: true }
    - { name: fb1_on,     write: true }
    - { name: fb2_on,     write: true }
    - any_on

The commands carry write so HA's automations and anybody in the HA UI can flip them — the glass and the phone stay in step because they move the same variable. any_on is read-only: a binary sensor.

4. The ladder

Three rungs:

1. Heartbeat — 1 Hz BLINK.
2. any_on — OR over fb1_on, fb2_on: the summary lamp counts what is actually lit.
3. All off — R_TRIG on the button, then a SEL per command writing false. One press, both commands cleared; the automations do the switching-off.

5. The screen

One landscape screen, two cards. Each card: a name, a bulb icon, the actual-state lamp (a state: colour set — yellow when lit), the command switch; the ceiling card adds the brightness slider with its percentage. The footer holds the All-off button. Nothing here is special — every element is on the widgets pages.

6. Download

Over the network or USB — F5. Within seconds HA shows ctrl32-f7lights with six entities.

---

The Home Assistant half

Four automations — two per light, command and feedback. Replace the light.… entity ids with your own.

Ceiling command — the switch or the slider changed, so drive the bulb (brightness comes along on every change):

alias: ctrl32 F7 lights - ceiling command
trigger:
  - platform: state
    entity_id: switch.ctrl32_f7lights_light1_on
  - platform: state
    entity_id: number.ctrl32_f7lights_light1_dim
action:
  - choose:
      - conditions:
          - condition: state
            entity_id: switch.ctrl32_f7lights_light1_on
            state: "on"
        sequence:
          - service: light.turn_on
            target:
              entity_id: light.your_dimmable_bulb
            data:
              brightness_pct: >-
                {{ states('number.ctrl32_f7lights_light1_dim') | int }}
    default:
      - service: light.turn_off
        target:
          entity_id: light.your_dimmable_bulb
mode: restart

Ceiling feedback — whatever the bulb really does lands back on the glass:

alias: ctrl32 F7 lights - ceiling actual state
trigger:
  - platform: state
    entity_id: light.your_dimmable_bulb
action:
  - choose:
      - conditions:
          - condition: state
            entity_id: light.your_dimmable_bulb
            state: "on"
        sequence:
          - service: switch.turn_on
            target:
              entity_id: switch.ctrl32_f7lights_fb1_on
    default:
      - service: switch.turn_off
        target:
          entity_id: switch.ctrl32_f7lights_fb1_on
mode: restart

The wall light gets the same pair without the brightness line.

---

Proving it

• Flip the ceiling switch on the glass: the bulb lights at the slider's percentage, the card's lamp follows a beat later — that beat is the round trip through the broker and back.
• Drag the slider: the bulb dims live.
• Turn the bulb off from the phone: the lamp on the glass goes dark, the header lamp with it.
• Press All off with both lights on: one press, both really off.

When it does not work