thompsonfw
@mthompson · Joined August 2025
Embedded developer · agriculture · 4 years in the field
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Perfect timing. I have a Pi 4 reading six energy meters over RS-485 with pymodbus. Which topic do the readings go to, and do the meters need their own tokens?
Good that Timed out is worded as “outcome unknown” and not as failed. On a weak cell link our boards often run the relay command and the reply is what gets lost.
Aisha’s right. And the catch is the ecosystem: very few meters speak it, so you’d be tied to that one vendor for the meters too. LoRaWAN meters are on the shelf from a dozen makers.
Nice. If the pumps ever need commands, keep in mind a reading batched for 15 minutes doesn’t delay those, they come down the open session.
Your colleague #2 is probably right. A full TLS handshake costs kilobytes, a keepalive ping is tiny.
SD corruption on power loss is the classic Pi failure. Overlay FS through raspi-config (Performance Options > Overlay File System) works well.
For the pucks: mount the gateway high and as close as you can, asphalt plus a car on top eats a lot of signal. We saw SF12 on half our in-ground sensors at first. Check the frames log for RSSI/SNR per sensor before you sign off any bay.
Moved to GPIO 26 with the HIGH-before-OUTPUT trick, no more click across 20 reboots. Bound the switch to pump_state and the firmware reports after switching. I had the old-reading option but not the unknown-state one, so the card was still clickable right after a restart. Both ticked now.
Ah. Any pin that stays quiet at boot?
WiFiManager does all of that for you, including custom fields on the page.
Built it last week. 2x2x0.5 shielded, auto-direction 485 modules, buck converters to 5 V at each Nano. All twelve answer at 19200 with zero CRC errors over two days. I forgot the bias resistors at first and got junk on node 11 (the far end) when the bus idled, adding them fixed it. Children show up in Hermetry as bench-01 to bench-12 under the gateway.
Could, but 12 radios and their power is more cost than a cable, and I want mains-powered nodes anyway.
That clears it up. Kept the footprints, fitting the crystal, and borrowed a NanoVNA for the matching once the enclosures arrive. The first prototype with only the 0 Ω in series already reaches the coordinator from 60 m, so the tuning should only make it better.
Unrelated to the menu thing, but make sure the ESP32 only ever pulses and never holds the relay, and that the door controller’s own limit switches and safety edge are what stop it. The board button should be a convenience, not the safety.
Got two STM32WL modules running on a test probe. The PIC sends three AT commands per reading over its spare UART, joins OTAA fine, and moisture shows up in Hermetry through a table codec. 28 to go. Thanks.