ESP32 Wi-Fi: joining the strongest access point on a mesh

Measured on a real ESP32 on 24 Oct 2026. Three access points, all on channel 2.

The board joined the weakest node (-79 to -84 dBm) instead of the nearest (-16 dBm). MQTT over WSS then failed with -0x7280 (MBEDTLS_ERR_SSL_CONN_EOF). Connecting took about 130 seconds.

With a full-channel scan sorted by signal, it joined the node at -15 to -17 dBm. Wi-Fi was up in 6.4 seconds. MQTT was up in 12.0 seconds. A shared attribute was received and applied 12.5 seconds after a hardware reset.

SDK option

AutoconnectoSDK 1.7.76 joins the strongest access point by default.

• config.wifiJoinStrongest = true scans every channel and sorts by signal. false keeps the first match.
• config.wifiConnectTimeoutMs defaults to 15 seconds.
• A failed MQTT connect switches between WSS and MQTTS, then retries with a bounded backoff.
• Register sdk.onWifiJoin before begin. It receives BSSID, channel, and RSSI even when enableSerialLogs is false. sdk.lastWifiJoin reads the same result.
• enableSerialLogs = false prints no SDK log lines. The sketch can still print the join callback.
• On boot the device takes the retained shared-attribute push. It does not send a second request when that push has already arrived.

examples/MqttConnectFault_mqtt fails the first two MQTT connects in software so the transport switch and the backoff can be checked without waiting for a dead broker.

Examples in the SDK:

• examples/WifiJoinStrongest_mqtt
• examples/Attributes_RestoreOnBoot_mqtt — read shared attributes at boot, drive a GPIO, and report a client attribute.
• examples/MqttConnectFault_mqtt

Next

• ESP32 quick start
• ESP32 MQTT
• This note on the website