$10 Matter over Thread Relay

I have Matter over Thread presence sensors. They were completely useless because there's nothing to control. The market has:

WiFi relays (Shelly, Sonoff) — no Thread
Zigbee relays (Aqara) — need proprietary hub
AC-only Matter switches — mains voltage, not dry contacts
Industrial Thread relays (Sunricher) — $20/unit, MOQ 30

Nobody makes a simple, cheap, Thread-based dry-contact relay. So I built one.

Bill of Materials

Component	Price
M5Stack NanoC6	~$6
M5Stack Unit Relay (U023)	~$4
Mini560 PRO 5V (optional)	~$1

The NanoC6 is an ESP32-C6 with a built-in 802.15.4 radio (Thread). The relay handles 30V DC or 220V AC at 3A with dry contacts. The Mini560 buck converter is optional — it lets you power everything from an existing 12-32V rail instead of needing a 5V USB source.

Wiring

[12-32V] ──→ [Mini560 IN+]
             [Mini560 IN-] ──→ GND
             [Mini560 OUT+] ──→ [NanoC6 Grove 5V (red)]
             [Mini560 OUT-] ──→ [NanoC6 Grove GND (black)]

[NanoC6 Grove Yellow] ──→ [Relay IN]
[NanoC6 Grove White]  ──→ NC (not used)

[Relay COM] ──→ [Load terminal A]
[Relay NO]  ──→ [Load terminal B]

The Mini560 output feeds directly into the Grove cable that connects the NanoC6 to the relay. One cable carries both power and signal.

Firmware

The device uses Espressif's esp-matter SDK on ESP-IDF, registering as an On/Off Light device type. You need ESP-IDF and esp-matter installed — follow Espressif's setup guide.

The key config: enable Thread + BLE commissioning, disable WiFi. In sdkconfig.defaults:

CONFIG_OPENTHREAD_ENABLED=y
CONFIG_OPENTHREAD_SRP_CLIENT=y
CONFIG_OPENTHREAD_DNS_CLIENT=y
CONFIG_BT_ENABLED=y
CONFIG_BT_NIMBLE_ENABLED=y
CONFIG_ENABLE_WIFI_STATION=n
CONFIG_ENABLE_WIFI_AP=n

The entire firmware is ~100 lines. The core is trivial — create a Matter node, add an on/off light endpoint, wire the attribute callback to a GPIO:

#define RELAY_GPIO GPIO_NUM_2  // Grove Yellow wire on NanoC6

static void set_relay(bool on)
{
    gpio_set_level(RELAY_GPIO, on ? 1 : 0);
}

static esp_err_t app_attribute_update_cb(
    attribute::callback_type_t type, uint16_t endpoint_id,
    uint32_t cluster_id, uint32_t attribute_id,
    esp_matter_attr_val_t *val, void *priv_data)
{
    if (type == PRE_UPDATE && endpoint_id == light_endpoint_id) {
        if (cluster_id == OnOff::Id && attribute_id == OnOff::Attributes::OnOff::Id) {
            set_relay(val->val.b);
        }
    }
    return ESP_OK;
}

extern "C" void app_main()
{
    nvs_flash_init();
    init_relay();

    node::config_t node_config;
    node_t *node = node::create(&node_config, app_attribute_update_cb, app_identification_cb);

    on_off_light::config_t light_config;
    light_config.on_off.on_off = false;
    endpoint_t *endpoint = on_off_light::create(node, &light_config, ENDPOINT_FLAG_NONE, NULL);
    light_endpoint_id = endpoint::get_id(endpoint);

    // Thread platform config (ESP32-C6 native 802.15.4 radio)
    esp_openthread_platform_config_t ot_config = {
        .radio_config = ESP_OPENTHREAD_DEFAULT_RADIO_CONFIG(),
        .host_config = ESP_OPENTHREAD_DEFAULT_HOST_CONFIG(),
        .port_config = ESP_OPENTHREAD_DEFAULT_PORT_CONFIG(),
    };
    set_openthread_platform_config(&ot_config);

    esp_matter::start(app_event_cb);
    PrintOnboardingCodes(chip::RendezvousInformationFlags(chip::RendezvousInformationFlag::kBLE));
}

Build and flash with idf.py set-target esp32c6 && idf.py build flash monitor. On first boot it prints a QR code — scan it with Apple Home (or any Matter controller) to commission over BLE. It joins your Thread network automatically.

How it works

[12/24V rail] → [Mini560 5V] → [NanoC6] → [Relay] → [Dry contacts]
                                  ↑
                            Matter over Thread

The NanoC6 registers as an On/Off Light on your Matter fabric. When any controller turns the "light" on, the attribute callback fires, GPIO 2 goes high, and the relay clicks.

The dry contacts can trigger anything: a Shelly SW input, a garage door opener, an HVAC system, a motorized valve — anything that accepts a dry contact closure.

I'm using mine to bridge a Lafaer LWR01 presence sensor to a Shelly Pro RGBWW PM via the Shelly's SW input, giving me presence-activated hallway lights through Apple Home automations.