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Metal cold room cabinet causes ESP-01 disconnects, external antenna options

Metal cold room cabinet causes ESP-01 disconnects, external antenna options

Solved 5 3

Translated from Türkçe by AI ·

Me again 🙂 This time it’s the hotel’s kitchen side. We monitor temperature in six cold rooms, each with a small box built from a DS18B20 + ESP-01 (ESP8266) that sends data to Hermetry every minute via MQTT. The boxes are inside the stainless steel electrical cabinet outside the room, and the probe cable goes inside.Two rooms keep disconnecting. On the device page’s Log tab I see keepalive_timeout 30-40 times a day, the offline alarm keeps switching on and off, and the night shift is tired of the alarm notifications. The access point is in the corridor, about 15 meters away.When I leave the cabinet door open it gets better, so the problem is probably the metal cabinet. Can an external antenna be attached to the ESP-01, or should I buy a different module? I don’t know much about electronics, a technician friend built the box inside the cabinet.

Modbus sadece register'dır, ta ki olmayana kadar.
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Translated from Türkçe by AI ·

What RSSI are you seeing? If you add WiFi.RSSI() to the telemetry in the code, you’ll see it on the graph instead of guessing.

Ağ geçidi yine bağlanıyor…
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Translated from Türkçe by AI ·

The technician added: with the lid closed between -86 and -91, when open -68.

Modbus sadece register'dır, ta ki olmayana kadar.
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Translated from Türkçe by AI ·

At -86 and below, the limit for ESP8266 is marginal, and the metal cabinet acts like a Faraday cage. The ESP-01 has a PCB antenna and no external antenna input. We had the same problem in our warehouse and solved it like this:We replaced the module with an ESP-07S or with the U.FL connector version of the ESP-12 (the ESP-07S has no PCB antenna, only U.FL, so there is no confusion). With an RP-SMA panel-type pigtail cable from the U.FL, we brought the antenna out through the top of the cabinet, and on the outside we fitted a small 3 dBi rod antenna. If you want to use an ESP32, the ESP32-WROOM-32U follows the same approach. The code does not change, only the pin definitions.Keep the cable short (20-30 cm), since a long thin coaxial cable causes losses at 2.4 GHz. Keep the antenna at least a few cm away from the metal surface of the cabinet, and keep it upright. For us, the signal went from -88 to -61.On the Hermetry side, also do this: check the Open after (seconds offline) value in the offline rule. The default is 600, but yours may have been set to something short like 60, so set it back to 600. Short disconnections will not open an alarm, and a device that really disconnects will still be caught within 10 minutes. Details: Offline alarmları. Also keep the keepalive in the 30-60 second range; the PubSubClient default is 15 seconds.

Accepted solution♥ 7

Translated from Türkçe by AI ·

Thanks a lot, Kerem. We fitted two rooms with ESP-07S and external antennas, RSSI is -63 / -66, and there have been no drops for two days. I also set the offline timeout to 600. The technician forgot to pull GPIO15 to ground while flashing the ESP-07S, and we struggled with it for half a day, so I’ll mention that too.

Modbus sadece register'dır, ta ki olmayana kadar.
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Translated from Türkçe by AI ·

Keep logging RSSI in telemetry. If you also set a threshold rule, you will get early warning if the antenna cable loosens.

Ağ geçidi yine bağlanıyor…
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