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By craigfoo
#76989 I've been working with AI-Thinker modules ESP-12E and then ESP-12S. I've come across a pulse issue during Deep Sleep Wake Up.

I have a simple setup to test individual modules and I'm experiencing different behavior with the same code and circuit on the different modules (ESP-12E vs. ESP-12S).

The schematic doesn't include the tie between RST and GPIO16 but I've tied them external for the Deep Sleep Wake Up requirement and measured the pulse. See attached for full schematic.

Redline of attached schematic showing external tie between RST and GPIO16:

ESP-12E Pulse:

ESP-12S Pulse:

Test Hardware, pogo pins to connect module:

Using EspressIf SDK, I ran a simple test to go into Deep Sleep and wake up automatically every 30 secs to capture the pulse. Code below, binaries attached.

Flashed binaries with esptool command:
Code: Select --port COM4 write_flash -ff 40m -fm dio -fs 4MB 0x0000 eagle.flash.bin 0x20000 eagle.irom0text.bin

Code: Select all
extern "C" {
#include "espressif/esp_common.h"
#include "gpio.h"
#include "uart.h"

 * FunctionName : user_rf_cal_sector_set
 * Description  : SDK just reversed 4 sectors, used for rf init data and paramters.
 *                We add this function to force users to set rf cal sector, since
 *                we don't know which sector is free in user's application.
 *                sector map for last several sectors : ABCCC
 *                A : rf cal
 *                B : rf init data
 *                C : sdk parameters
 * Parameters   : none
 * Returns      : rf cal sector
extern "C" uint32 user_rf_cal_sector_set(void) {
    // FIXME - Is this using the correct part of the flash?
    flash_size_map size_map = system_get_flash_size_map();
    uint32 rf_cal_sec = 0;

    switch (size_map) {
    case FLASH_SIZE_4M_MAP_256_256:
        rf_cal_sec = 128 - 5;

    case FLASH_SIZE_8M_MAP_512_512:
        rf_cal_sec = 256 - 5;

    case FLASH_SIZE_16M_MAP_512_512:
    case FLASH_SIZE_16M_MAP_1024_1024:
        rf_cal_sec = 512 - 5;

    case FLASH_SIZE_32M_MAP_512_512:
    case FLASH_SIZE_32M_MAP_1024_1024:
        rf_cal_sec = 1024 - 5;
    case FLASH_SIZE_64M_MAP_1024_1024:
        rf_cal_sec = 2048 - 5;
    case FLASH_SIZE_128M_MAP_1024_1024:
        rf_cal_sec = 4096 - 5;
        rf_cal_sec = 0;
    // ets_printf("Size map %d \n", size_map);
    return rf_cal_sec;

 * user_init - Entry point into our application.  We must initialize our app
 * and return from this function to allow the SDK built-in threads to start
 * and execute.
extern "C" void user_init(void) {
  printf("SDK version:%s\n", system_get_sdk_version());

  system_deep_sleep_set_option(0); // Use EEPROM to determine RF on wake behavior

Can anyone else run this test and see what they get? I've contacted AI-Thinker about it but so far they aren't being helpful. I've also contacted EspressIf and they ran this test on their WROOM-02 module and the pulse looks great. The reason I'm concerned is that sometimes the ESP8266 "hangs" when coming out of Deep Sleep, it's random but I have a hunch it's because of this less than ideal wake up pulse.
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User avatar
By craigfoo
#77279 I found the culprit.

I ended up removing the shields on both the ESP-12S and ESP-12E to try to track down the differences. There is one major difference that, so far, has not been documented anywhere (even by AI-Thinker).

The schematics of the modules that have been floating around are not 100% correct. Even the schematic from the AI-Thinker documentation for the ESP-12E is incorrect.

In the ESP-12E module, there is a series resistor (about a 450 Ohm) in series between the RST pad and the EXT_RSTB of the ESP8266. There is also a 12k pull-up and some value capacitor. Seems like the RC circuit slows the rise time for the reset. This 450 Ohm resistor doesn't exist in the ESP-12S module which isn't documented anywhere.

Adding this 450 Ohm resistor in series externally on the ESP-12S fixes the pulse issue.

User avatar
By Andres Petrillo
#82063 Hi @craigfoo.
We are having a similar issue with a batch of ESP12F. ... -487568675

Can you post a picture or a diagram of how you solved the problem with an external resistance? I can not understand between what pins that resistance would go.