Esp-01 01s Apr 2026

| Feature | ESP-01 | ESP-01S | |---------|--------|---------| | Flash | 512 kB (rare 1 MB) | 1 MB | | Pull-ups on GPIO0,2,EN | No | Yes (12k) | | User LED | No (red power only) | Yes (blue on GPIO2) | | Boot reliability | Poor without mods | Good | | AT firmware version | v0.x–v1.x | v1.x–v2.x | | Best for | Hobbyist with soldering | Reliable IoT endpoints |

Always buy ESP-01S unless you have a specific need for the original's smaller flash (almost never). For anything beyond two I/O pins, skip both and use ESP-12E/F, Wemos D1 Mini, or NodeMCU. esp-01 01s

Once connected:

| Mode | GPIO0 | GPIO2 | GPIO15 | |------|-------|-------|--------| | UART Download (Flash) | LOW | HIGH | LOW | | Flash Boot (Run) | HIGH | HIGH | LOW | | SDIO/SPI Boot | ? | ? | HIGH (invalid for ESP-01) | #define DHTPIN 0 #define DHTTYPE DHT11

#include <ESP8266WiFi.h> #include <PubSubClient.h> #include <DHT.h> #define DHTPIN 0 #define DHTTYPE DHT11 skip both and use ESP-12E/F