ESP-01S Pinout


The ESP-01S module is equipped with just 8 pins. Among these pins, two are designated for power, denoted as VCC and GND. Additionally, two pins serve the functions of enabling (EN) and resetting (RST) the module.

Pin Function Notes Pull Up
1 GND  Power Ground
2 GPIO1 Default Serial TX
(ESP-01S -> MCU)
3 GPIO2 Serial1
(ESP-01S -> MCU)
4 CHIP_EN Chip Enable
5 GPIO0 Yes
LOW to HIGH reset the chip
7 GPIO3 Default Serial RX
(ESP-01S <- MCU)
8 VCC Power VCC 2.5-3.6V

This allocation leaves us with a total of four General-Purpose Input/Output (GPIO) pins at our disposal. These GPIO pins are identified as GPIO0, GPIO1, GPIO2, and GPIO3. However, it's important to note that GPIO1 and GPIO3 are reserved for specific purposes, namely serving as the transmit (TX) and receive (RX) pins for serial communication.

For instance, if you require serial data transmission, such as interacting with the Arduino IDE's Serial Monitor, these two pins are dedicated to that purpose. Consequently, only two pins (GPIO0 and GPIO2) remain available for general GPIO usage on the ESP-01S module. This limitation underscores the importance of judiciously planning your pin assignments for your specific project needs.

Powering the ESP-01S

The ESP-01S module lacks an onboard Low-dropout regulator (LDO). Instead, the VCC pin is directly connected to the ESP8266 System-on-Chip (SoC). According to the ESP8266 datasheet, the recommended operating voltage falls within the range of 2.5V to 3.6V. Therefore, a stable 3.3V power supply is highly recommended for the VCC pin. If you intend to power the ESP-01S via a USB port, you will need an external Fixed 3.3V LDO (Low-dropout regulator). A commonly employed LDO for this purpose is the AMS1113.

It's crucial to note that the ESP-01S has a maximum allowable voltage of 3.6V. This imposes a limitation when attempting to power the module directly from certain power sources, such as LIPO batteries like the 18650 battery, which can have a voltage as high as 4.2V when fully charged. In such cases, the implementation of an LDO becomes indispensable to effectively lower the input voltage from the LIPO battery to the safe operating range of the ESP-01S, ensuring optimal performance and preventing potential damage.



The CHIP_EN (Chip Enable) Pin, found at Pin 4, is a pivotal control feature responsible for activating or deactivating the ESP8266 chip integrated within the ESP-01S module. When this pin is set to a logic HIGH level (connected to VCC or 3.3V), it serves as the switch that empowers the ESP8266 chip, enabling it to execute its program or firmware seamlessly. Conversely, should CHIP_EN be driven to a logic LOW level (connected to GND), it acts as the switch-off mechanism for the ESP8266 chip. In this state, the chip is effectively rendered inactive or placed into a low-power mode, thereby conserving energy. Analogous to a power switch on a personal computer, this pin governs the operational status of the ESP8266 chip.

The EXT_RSTB (External Reset) Pin, positioned at Pin 6, serves as a conduit for external hardware or software-driven resets for the ESP-01S module. When the need arises to initiate a reset sequence, the process involves transitioning this pin from a logic LOW level (connected to GND) to a logic HIGH level. This action triggers a reset event, effectively restarting the ESP8266 chip. It's important to note that when the EXT_RSTB pin is pulled to a logic LOW state, the ESP-01S ceases its operations, and only upon returning the pin to a logic HIGH state does the ESP-01S recommence its functioning. Similar to the reset switch on a PC.

In essence, while both CHIP_EN and EXT_RSTB contribute to the management of the ESP8266 chip within the ESP-01S module, their roles are distinctly separate. CHIP_EN chiefly governs the chip's activation and deactivation, resembling a power switch, whereas EXT_RSTB offers an avenue for external resets to restart or reset the chip as required. Understanding the unique functions of these pins is crucial for maintaining control and ensuring the desired behavior of the ESP-01S module.

Todo Video: Chip_EN connect to switch, EXT_RST connect to reset button


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