Uno + ESP-01 as a small bridge for a street-cabinet energy logger prototype (the ESP has its own sketch, Uno sends it lines over serial). ESP VCC and CH_PD go to the Uno’s 3.3 V pin, GND common.
Sometimes it connects and runs for hours. Most times it reboots in a loop the moment it starts Wi-Fi:
ets Jan 8 2013,rst cause:2, boot mode:(3,6)
load 0x4010f000, len 3460, room 16
...
ets Jan 8 2013,rst cause:4, boot mode:(3,6)
wdt resetWhen it does stay up, Hermetry shows it dropping off every half hour or so, Log tab says keepalive_timeout. Is the 3.3 V pin the problem or my code? I’ve read both opinions.
I had the same reboot loop and it was my code calling delay() too long, so the watchdog bit me. Check for long loops without yield()
Possible, but with the pin you’re using I’d bet on power first. The Uno’s 3.3 V comes from a small LDO (an LP2985 on most boards) rated about 150 mA. An ESP8266 pulls 70-80 mA idle with Wi-Fi on and spikes to 300+ mA during transmit and association. The rail sags, the ESP browns out mid-connect and resets. When it does survive, every busy moment risks the same, which fits your half-hourly drop-offs.
What I’d do:
- Feed the ESP from its own regulator off the Uno’s 5 V: an AP2112K-3.3 (600 mA) or an AMS1117-3.3 module, with 10 µF plus 100 nF right at the ESP’s VCC pin. A 470 µF electrolytic nearby helps with the transmit spikes.
- Level-shift Uno TX to ESP RX with a 1k/2k divider. The ESP isn’t 5 V tolerant, whatever forum posts claim.
- Keep the Uno’s 5 V source decent. USB from a laptop is fine for the bench, a cheap phone charger often isn’t.
Michael’s point is worth checking after that. rst cause 4 is the watchdog, and a brownout that half-crashes the code can also end in a watchdog reset, so fix power and see what’s left.
For the Hermetry side, once it’s stable, keep the MQTT keepalive around 60 s. A short keepalive plus a flaky supply gives you exactly that pattern of timeouts in the Log tab.
That was it. AP2112 module with 470 µF on the ESP, no reboots since Monday, and the keepalive_timeouts are gone from the Log tab. I had the divider already. Scoped the old 3.3 V rail out of curiosity: it dipped to 2.6 V on every connect.
fair enough, power first next time
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