ESP8266 Software Serial Loopback Test

This is a quick summary of testing the software serial function on a single ESP8266 in loopback mode.

Schematic

For this post, GPIO14 and GPIO12 are used as the RX and TX respectively for Software Serial.

Note,
For ESP8266, GPIO 0 ~ 5, 12 ~ 15 can be used for RX / TX, GPIO 16 cannot be used for RX / TX.

Arduino Sketch

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/* The original example can be found at https://github.com/esp8266/Basic/tree/master/libraries/espsoftwareserial * Implementation of the Arduino software serial library for the ESP8266. * Speed up to 115200 baud is supported. The constructor also has an optional input buffer size. * Please note that due to the fact that the ESP always have other activities ongoing, there will be some inexactness in interrupt timings. * This may lead to bit errors when having heavy data traffic in high baud rates. * * https://forum.arduino.cc/index.php?topic=354933.0 * For ESP8266, GPIO 0 ~ 5, 12 ~ 15 can be used for RX / TX, GPIO 16 cannot be used for RX / TX. * * The circuit: * RX is digital pin 14 (connect to TX of other device) * TX is digital pin 12 (connect to RX of other device) */ #include <SoftwareSerial.h> String str = ""; SoftwareSerial swSer(14, 12, false, 256); // rxPin, txPin, inverse_logic, buffer size void setup() { Serial.begin(115200); swSer.begin(115200); // Max speed for software serial is 115200bps // clear out the serial buffer // https://forum.arduino.cc/index.php?topic=234151.0 // ----------------------------------------------------------------------------------------------------- byte w = 0; for (int i = 0; i < 10; i++) { while (Serial.available() > 0) { char k = Serial.read(); w++; delay(1); } delay(1); } // ----------------------------------------------------------------------------------------------------- Serial.println(); //Serial.print("***SSSoooffftttwwwaaarrreee...ssseeerrriiiaaalll...ttteeesssttt...ssstttaaarrrttteeeddd***"); Serial.print("***Software.serial.test.started***"); while (swSer.available() > 0) { str = str + (char)swSer.read(); yield(); } Serial.println(); Serial.print("Message received via software serial: "); Serial.println(str); Serial.println("\nEnd of message received"); } void loop() { yield(); }

Note,

Line 41 may be implemented to counter error during transmission. It's inspired by the Forward Error Correction (FEC) taught in this video - https://www.youtube.com/watch?v=0CLTy231Hsw.

Result

References:

https://github.com/esp8266/Basic/tree/master/libraries/espsoftwareserial

https://forum.arduino.cc/index.php?topic=354933.0