Some notes on some boards I have tried.

Flashing requires holding down USER button on boot. The meshtastic device installer script needs it held for some time as it flashes multiple images, resetting in between.

Meshtastic firmware build as of 25 Oct 2023 did not work on the boards I had, because it seems the screen / connection was changed by Heltec in newer versions of the board. Screen working with build of git master which was at 092e6f2424aac486267c15e1c94f18c36093017a.

Flashing this with platformio uses a different method. It uses the builtin jtag interface of the ESP32, which does not use the CDC-ACM serial port. This is significant because permissions on the USB device must be set correctly, not just on the serial port.

udev rule to add:

ATTRS{idVendor}==“303a”, ATTRS{idProduct}==“1001”, MODE=“0660”, GROUP=“plugdev”, TAG+=“uaccess”

Tested output with spectrum analysers - Rigol RSA5032 TG, and Siglent SSA 3021X, on 28th Nov 2023. Could just about see the chirps on waterfall display.

Used Meshtastic with settings: Very long slow, +27dBm TX. Bandwidth should be 62.5 kHz. Centre frequency 869.4313MHz. Tested in room temperature room. Git version 092e6f2424aac486267c15e1c94f18c36093017a, screen says 2.2.12.

Using max hold setting, peak was a flat line across expected bandwidth, power about 20dBm. Allowing for losses in cables and connectors, perhaps about 21.5dBm out of the board. Board uses SX1262 which specifies: “+22dBm or +15dBm high efficiency PA”. It seems we have a 22dBm transmitter and it is basically hitting its specification.

Centre frequency was low by about 1kHz (~1.2ppm). Seems oscillator is well tuned, at least at room temp. Bandwidth at about -1dB about 62 kHz. Not sure how at what level the specified bandwidth is meant to be measured.

Noticed later that despite UI showing 869.4313MHz, serial console shows radio is set to 869.431274 MHz - 26 Hz lower than specified. It seems that when not set explicitly, the code calculates a centre frequency from the bandplan, so I suspect that the UI is then showing a rounded value. Explicitly setting 869.4313MHz would give the set value I think.

Console also says Set radio: final power level=22. This appears to come from #define SX126X_MAX_POWER 22 in SX126xInterface.cpp.

2nd harmonic ~47dB down from peak. Otherwise output looked clean.

This was straightforward to flash with Meshtastic.

The WiFi is terrible. Probably because of the small helical coil antenna. It seems to need an AP very close to connect.

This was straightforward to flash with Meshtastic.

It has two antenna connectors, one for LoRa, and one for wifi / bluetooth? I could not find any documentation for this, but a forum post somewhere said the connector for LoRa is the one on the top left.

There are several versions. I (river) have a version marked “T-BEAM-AXP2101-V1.2”.

Parts:

• ESP32-D0WD (original, not S2/3)
• SX1276
• NEO-6M GPS
• AXP2101 power control chip
• CH9102F - WCH USB serial chip.
• MS412FE rechargeable RTC backup battery connected to GPS.
• micro USB. (Other boards I have have USB C)

Power on seems to require long press on PWR button.

Screen connects to pins 21 and 22 which are also marked SDA and SCL.

Supplied antenna is marked LILYGO/868. SMA connector on board. Not tested yet.

uFL for GPS, supplied with small antenna. uFL for wifi / bluetooth or ?default onboard sheet metal antenna.

It came with meshtastic installed, with limited web interface. Latest meshtastic build failed to flash with MD5Sum error. It at least partially worked but webserver only had basic interface. Latest release build worked as expected with full web interface. File that worked:

./device-install.sh firmware-tbeam-2.1.23.04bbdc6.bin

I have since found that the md5 error goes away if programming speed is reduced to 115200 baud. This is surprising as I normally find 1.5 MBaud works reliably for programming ESP8266 with CH340.

esptool reports:

Chip is ESP32-D0WDQ6-V3 (revision v3.1) Features: WiFi, BT, Dual Core, 240MHz, VRef calibration in efuse, Coding Scheme None Crystal is 40MHz

User: Red, connected to GPIO4. Middle left, over charge LED. Charge: Blue. Connected to AXP2101 power control chip. GPS: Red, under the GPS module. Connected to the PPS output.

• SX127x on RFM9x module.
• ATSAMD21G18 ARM Cortex M0 processor
• Needs uFL connector added.

Not supported by meshtastic or RNode.

• Marked 20170815
• SX1278
• ESP32-DOWD
• CP2102