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When using Arduino SoftwareSerial with ESP8266, the blue led turns always on every time I reset the circuit by power. The only way to take the ESP working again is reflashing with the SDK 2.2.1, AT Firmware.

  • Have tested AMS1117 and LM317 as Power supply;
  • I'm using level converter 3V3 <-> 5V;
  • Have choosen different pins on Arduino for TX and RX;
  • No problem when using Hardware Serial pins with no SoftwareSerial;
  • My application works fine. The problem arises when I power off and power on and using SoftwareSerial.

Have noted a difference on the startup of ESP8266 after it gets stuck.

Here is the original startup (at 74880bps), ESP working normally

 ets Jan  8 2013,rst cause:2, boot mode:(3,6)

load 0x40100000, len 2592, room 16 
tail 0
chksum 0xf3
load 0x3ffe8000, len 764, room 8 
tail 4
chksum 0x92
load 0x3ffe82fc, len 676, room 4 
tail 0
chksum 0x22
csum 0x22

2nd boot version : 1.7(5d6f877)
SPI Speed : 40MHz
SPI Mode : QIO
SPI Flash Size & Map: 8Mbit(512KB+512KB)
jump to run user1 @ 1000

rf cal sector: 251
freq trace enable 1
rf[112] : 03
rf[113] : 00
rf[114] : 01
w_flash <-- check the presence of this word

SDK ver: 2.2.1(6ab97e9) compiled @ Jun  7 2018 13:59:14
phy ver: 1136_0, pp ver: 10.2

⸮⸮j⸮l <-- here ESP is ready for AT commands at 115200bps. This is the word "ready" at 115200

Now, when the problem arises

 ets Jan  8 2013,rst cause:2, boot mode:(3,6)

load 0x40100000, len 2592, room 16 
tail 0
chksum 0xf3
load 0x3ffe8000, len 764, room 8 
tail 4
chksum 0x92
load 0x3ffe82fc, len 676, room 4 
tail 0
chksum 0x22
csum 0x22

2nd boot version : 1.7(5d6f877)
SPI Speed : 40MHz
SPI Mode : QIO
SPI Flash Size & Map: 8Mbit(512KB+512KB)
jump to run user1 @ 1000

rf cal sector: 251
freq trace enable 1
rf[112] : 03
rf[113] : 00
rf[114] : 01

SDK ver: 2.2.1(6ab97e9) compiled @ Jun  7 2018 13:59:14
phy ver: 1136_0, pp ver: 10.2

Someone knows what w_flash means?

  • SoftwareSerial at 115200 baud does not work. – Majenko Sep 12 '19 at 10:40
  • 1
    cause: 2 is never good. your esp8266 is underpowered or has to high RF TX power enabled – Juraj Sep 12 '19 at 11:02
  • @Majenko On Arduino, SoftwareSerial sends command to ESP to change to 19200 baud. Then runs SoftSerial.begin(19200) – LeandroIP Sep 12 '19 at 11:51
  • 1
    @LeandroIP - SoftwareSerial won't be able to send the command reliably if it is set to 115200 to start with. I suspect its your power supply, do your PSUs push out enough amp? (can't remember what an ESP8266 requires) – Code Gorilla Sep 12 '19 at 15:27
  • Please note: 1. SoftwareSerial will not work at those high frequencies. And, please, be clear about your setup. Are you using SS on the arduino or on the esp? What pins? How are both circuits powered? – Marco Tulio Souza Sep 13 '19 at 1:31

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