4 ms·

> Simple home-made driver for the SX1276 and SX1262 LoRa chip Beware of what nailed the Meshtastic people: These chips don't have temperature dependent crystal

> Simple home-made driver for the SX1276 and SX1262 LoRa chip Beware of what nailed the Meshtastic people: These chips don't have temperature dependent crystal oscillators. Transmitting more than a few milliseconds causing a temperature rise, throwing the clock off, causing transmission warpage, causing timing errors, causing transmission failures.

Neywiny 1y ago
You mean they don't have temperature compensated? What you described is temperature dependent
- exabrial 1y ago
  too late to edit now :)
bigfatkitten 1y ago
This is a radio module issue, not a chip issue. Cheap modules have cheap crystals, better ones have a TCXO.
ShakataGaNai 1y ago
Temperature Compensated Crystal Oscillators (TCXOs) is what they should be looking for. And to be clear you can get SX1262 variants with such, eg: https://wiki.seeedstudio.com/wio_sx1262/ https://wiki.seeedstudio.com/wio_sx1262/ For the detailed run down, see https://cdn.sparkfun.com/assets/f/f/b/4/2/SX1262_AN-Recommendations_for_Best_Performance.pdf https://cdn.sparkfun.com/assets/f/f/b/4/2/SX1262_AN-Recommen... page 14 > In the case of an SX1262 operating at +22 dBm in the US 902 – 928 MHz band, the frequency drift measured during the maximum LoRAWAN™ packet duration stays below the maximum limit, provided thermal insulation is implemented around the crystal during PCB design. > At extreme temperatures (below -20 °C and above 70 °C), it is recommended to use a TCXO. > For any other frequency bands corresponding to longer RF packet transmissions at +22 dBm, it is recommended to use a TCXO.
- buckle8017 1y ago
  Theory and reality are different here. As used in the meshtastic devices this chip does actually fail doing normal Lora transmission under reasonable conditions. I know because I've seen the exact failure.
  - nerdsniper 1y ago
    You've seen the failures in variants with a TCXO?
oakwhiz 1y ago
The chip itself supports using a TCXO instead of a regular crystal

Neywiny 1y ago

You mean they don't have temperature compensated? What you described is temperature dependent

exabrial 1y ago
too late to edit now :)

bigfatkitten 1y ago

This is a radio module issue, not a chip issue. Cheap modules have cheap crystals, better ones have a TCXO.

ShakataGaNai 1y ago

Temperature Compensated Crystal Oscillators (TCXOs) is what they should be looking for. And to be clear you can get SX1262 variants with such, eg: https://wiki.seeedstudio.com/wio_sx1262/ https://wiki.seeedstudio.com/wio_sx1262/ For the detailed run down, see https://cdn.sparkfun.com/assets/f/f/b/4/2/SX1262_AN-Recommendations_for_Best_Performance.pdf https://cdn.sparkfun.com/assets/f/f/b/4/2/SX1262_AN-Recommen... page 14 > In the case of an SX1262 operating at +22 dBm in the US 902 – 928 MHz band, the frequency drift measured during the maximum LoRAWAN™ packet duration stays below the maximum limit, provided thermal insulation is implemented around the crystal during PCB design. > At extreme temperatures (below -20 °C and above 70 °C), it is recommended to use a TCXO. > For any other frequency bands corresponding to longer RF packet transmissions at +22 dBm, it is recommended to use a TCXO.

buckle8017 1y ago
Theory and reality are different here. As used in the meshtastic devices this chip does actually fail doing normal Lora transmission under reasonable conditions. I know because I've seen the exact failure.
- nerdsniper 1y ago
  You've seen the failures in variants with a TCXO?

oakwhiz 1y ago

The chip itself supports using a TCXO instead of a regular crystal