On the ESP32 bench
An ESP32 has no LoRa radio, so a module on SPI and an antenna do the work, and both ends must agree on every setting. This lesson wires the bench in 3D and shows why a mismatch is silence, not an error.
The ESP32 has no LoRa radio
The ESP32 family has Wi-Fi and Bluetooth built in. None of its chips has a sub-gigahertz LoRa transceiver. A LoRa link needs an external radio, a transceiver chip or a module built around one, with an antenna.
The wiring
The usual modules are built on a Semtech SX126x or SX127x chip, and they talk to the ESP32 over SPI: a clock, two data lines and a chip select, plus a reset line and at least one interrupt line. The exact pins differ by chip and by module, so the bench draws a generic one. Wire a real one from its own pinout.
What has to match
For two ends to hear each other, the frequency, the spreading factor, the bandwidth and the sync word must agree. So must the header mode and the check setting. A private network commonly uses a sync word of 0x12, and LoRaWAN uses 0x34, so a private pair and a LoRaWAN gateway do not match.
Here is the cost. A receiver cannot report a packet it could not demodulate. A mismatch does not produce an error. It produces nothing. Change one setting at a time, and compare both cards against the datasheet before you suspect the code.
The antenna comes first
Connect the antenna before the module transmits. With none, the link is far weaker, and the output stage has nothing sensible to drive, so a reflection can send power back into it. A free-space quarter wave at 915 MHz is about eight centimetres, which is a starting point only. A real antenna is tuned to its ground plane and its housing.
The frequency must be allowed
The module has to be built for the band you use, and the frequency has to be one the rules allow where you are, as lesson seven showed. The wiring and the code are in the LoRa chapter of the ESP32 book. For the contrast, the ESP32's own radio is the subject of the Wi-Fi course.
Common mistakes
- Calling an ESP32 a LoRa device. The chip has no sub-gigahertz radio. The module and the antenna are separate parts, and each must be right.
- Changing two settings at once. A mismatch looks like silence, so you cannot tell which change caused it. Change one thing and check the cards.
- Transmitting before the antenna is on. The bench shows nothing arriving. On real hardware the output stage pays for it.
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