ESP8266: Pinout, Minimal Circuit and Technical Specifications

Introduction

In recent years the ESP8266 has become one of my go-to choices for smart home/IoT devices or projects requiring WiFi. It is cheap (around $1.5 on Amazon)¹, has WiFi, and can be programmed using the Arduino IDE, making it an easy replacement for Arduinos if we need WiFi connectivity.

This post concentrates on the technical specifications of different ESP8266 modules and the minimal circuit required to use each ESP module. It is part of a complete ESP8266 reference you can find here.

Technical Specification

The information in this chapter is primarily taken from the datasheets of the different modules [8,9,10,11,12].

Power:

• Supply Voltage: 2.8-3.6V
• avg. current: 80mA
• Max current: 430mA
• avg. Light Sleep current: 0.4-1.8mA
• avg. Deep Sleep current: 20µA

Memory:

• RAM: 80kB
• Cache: 32kB
• Flash Memory: up to 16MB external flash
• Max Program size: 1MB

Connectivity:

• Digital I/O: 11 programmable pins, 12mA max.
• Analog in: 1 pin, 0-1V, 10 bit resolution
• Serial: 1 SPI, 1 IIC, 1 UART, 1 UART (output only)
• WiFi: 802.11 b/g/n 2.4GHz, WPA/WPA2 PSK
• IPv4 and IPv6 (with Arduino Core 2.5.0 or later)
• UDP and TCP, max 5 simultaneous connections
• Ping: 4-10ms (up to 200 on crowded channels)
• Soft-AP, up to 4 simultaneous connections

ESP-01 and ESP-1

The ESP-01 and ESP-1 modules are among the cheapest options. They feature eight exposed pins (2.54mm pin header), of which only two are usable GPIO pins. The modules differ in the following way:

Module	Flash memory	LEDs	Other
AI-Thinker ESP-01	512kB (blue) or 1MB (black)	Power (red), GPIO2 (green)
AZ-Delivery ESP-01S	1MB	GPIO2 (blue)	additional pull-up resistor on EN pin
DOIT ESP-1 (ESP82855)	1MB	TxD (blue)

Minimal Circuit

The minimal circuit required to run an ESP-01 is shown in Fig. 2.1 below. Pins 2, 4, and 6 need to be connected to VCC, while pin 7 has to be connected to ground. Pulling pin 3 low during boot enables the firmware upload mode. As always, a decoupling capacitor is placed close to the microcontroller.

Pinout

Pin No.	Name	Description	Behavior on boot
1	GPIO3 (RxD)	Serial input/GPIO	pulled high
2	VCC	+3.3V, uses up to 430mA	pulled high
3	GPIO0	low on boot to enter programming mode, high or floating for normal boot
4	RESET	low to reset, see Fig. 2.2
5	GPIO2 (TxD1)	normal gpio	serial output, not allowed to be low
6	CHIP_EN	high to enable chip, low to shut down
7	GND	ground
8	GPIO1 (TxD)	serial output or normal gpio	serial output, not allowed to be low

Reset Pin differences

Furthermore, the modules differ slightly in how the reset pin circuit is realized. Figure 2.2 below shows how the module's pin 1 (labeled "1") is connected to the ESP8266's reset pin (labeled "RST").

ESP-07 and ESP-12

In contrast to the ESP-01 module, the ESP-07 and ESP-12 modules have additional flash memory and more exposed pins. While the ESP-07 has 16 exposed pins, the ESP-12E and F modules have 22 pins, of which six are unusable.

Module	Flash memory	LEDs	Other
ESP-07	1MB	Power (red), GPIO2 (blue)	Built in ceramic antenna, external antenna can be used (remove capacitor!)
ESP-07S	1MB	no LEDs	requires external antenna
ESP-12S	4MB	GPIO2 (blue)	built in antenna only
ESP-12E ESP-12F	4MB	GPIO2 (blue)	built in antenna only 6 additional, unusable, pins

Minimal Circuit

Although the minimal circuit required to run the ESP-07 and ESP-12E/F is similar to ESP-01's, the pinout has changed. Pins 1, 3, and 8 need to be connected to VCC, while pin 7 has to be connected to ground. Additionally, pin 16 (gpio15) has to be pulled LOW during boot. Pulling pin 18 (gpio0) low during boot enables the firmware upload mode. Again, a decoupling capacitor is placed close to the microcontroller.

Pinout

Pin No.	Name	Description	Behavior on boot
1	RESET	low to reset, see Fig. 2.4
2	ADC	analog input, 0-1V
3	CHIP_EN	high to enable chip, low to shut down
4	GPIO16	gpio (no PWM), wakeup timer output when using deep sleep	emits high pulse
5	GPIO14 (SCK)	normal gpio or serial clock (SPI)	pulled high
6	GPIO12 (MISO)	normal gpio or master input slave output (SPI)	pulled high
7	GPIO13 (MOSI)	normal gpio or master output slave input (SPI)	pulled high
8	VCC	+3.3V, uses up to 430mA	pulled high
9		already used to connect to built-in flash memory
10
11
12
13
14
15	GND	ground
16	GPIO15 (CS)	normal gpio or chip select (SPI)	has to be pulled low
17	GPIO2 (TxD1)	normal gpio, connected to blue LED (illuminate on low)	serial output, not allowed to be low
18	GPIO0	low on boot to enter programming mode, high or floating for normal boot
19	GPIO4	normal gpio
20	GPIO5	normal gpio
21	GPIO3 (RxD)	Serial input/GPIO	pulled high
22	GPIO1 (TxD)	serial output or normal gpio	serial output, not allowed to be low

Reset Pin differences

Furthermore, the modules differ slightly in how the reset pin circuit is realized. Figure 2.2 below shows how the module's pin 1 (labeled "1") is connected to the ESP8266's reset pin (labeled "RST").

Limitations

Although the ESP8266 is a great chip, it has several drawbacks.

• The analog input has up to 20% error [8]. Turning off WiFi before reading an analog signal can help reduce the error, as discussed in [1].
• Waking up from deep sleep requires a reset of the chip, causing data in RAM to be lost.
• The RTC is inaccurate in deep-sleep.
• ESP.deepSleep() sometimes does not enter deep sleep correctly [1,6]. Using delay(100) after ESP.deepSleep() helps to mitigate this problem.
• The ESP has no real multitasking, so we must give the WiFi enough time to do the required tasks. This is done in between calls to loop() or during delay() or yield() calls, as discussed in [13]. If not, the ESP's watchdog resets the module.

More Info

This post is part of a complete ESP8266 reference/guide. You can find more information on how to use your ESP8266 module effectively at blog.hirnschall.net/esp8266/.

References

Visited on 26.06.2023:

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