diff --git a/cores/esp8266/core_esp8266_sigma_delta.c b/cores/esp8266/core_esp8266_sigma_delta.c
new file mode 100644
index 0000000000..d101401c2e
--- /dev/null
+++ b/cores/esp8266/core_esp8266_sigma_delta.c
@@ -0,0 +1,174 @@
+/*
+  core_esp8266_sigma_delta.c - sigma delta library for esp8266
+  
+  Copyright (c) 2014 Ivan Grokhotkov. All rights reserved.
+  This file is part of the esp8266 core for Arduino environment.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+#include "Arduino.h" // using pinMode
+
+// definitions in esp8266_peri.h style
+#define GPSD  ESP8266_REG(0x368) // GPIO_SIGMA_DELTA register @ 0x600000368
+#define GPSDT 0  // target, 8 bits
+#define GPSDP 8  // prescaler, 8 bits
+#define GPSDE 16 // enable
+
+void sigmaDeltaSetPrescaler(uint8_t prescaler); // avoids compiler warning
+
+/******************************************************************************
+ * FunctionName : sigmaDeltaEnable
+ * Description  : enable the internal sigma delta source
+ * Parameters   : none
+ * Returns      : none
+*******************************************************************************/
+void ICACHE_FLASH_ATTR sigmaDeltaEnable()
+{
+  GPSD = (0 << GPSDT) | (0 << GPSDP) | (1 << GPSDE); //SIGMA_DELTA_TARGET(0) | SIGMA_DELTA_PRESCALER(0) | SIGMA_DELTA_ENABLE(ENABLED)
+}
+
+/******************************************************************************
+ * FunctionName : sigmaDeltaDisable
+ * Description  : stop the internal sigma delta source
+ * Parameters   : none
+ * Returns      : none
+*******************************************************************************/
+void ICACHE_FLASH_ATTR sigmaDeltaDisable()
+{
+  GPSD = (0 << GPSDT) | (0 << GPSDP) | (0 << GPSDE); //SIGMA_DELTA_TARGET(0) | SIGMA_DELTA_PRESCALER(0) | SIGMA_DELTA_ENABLE(DISABLED)
+}
+
+/******************************************************************************
+ * FunctionName : sigmaDeltaAttachPin
+ * Description  : connects the sigma delta source to a physical output pin
+ * Parameters   : pin (0..15), channel = unused, for compatibility with ESP32
+ * Returns      : none
+*******************************************************************************/
+void ICACHE_FLASH_ATTR sigmaDeltaAttachPin(uint8_t pin, uint8_t channel)
+{
+  (void) channel;
+  // make the chosen pin an output pin
+  pinMode (pin, OUTPUT);
+  if (pin < 16) {
+    // set its source to the sigma delta source
+    GPC(pin) |= (1 << GPCS); //SOURCE 0:GPIO_DATA,1:SigmaDelta
+  }
+}
+
+/******************************************************************************
+ * FunctionName : sigmaDeltaDetachPin
+ * Description  : disconnects the sigma delta source from a physical output pin
+ * Parameters   : pin (0..16)
+ * Returns      : none
+*******************************************************************************/
+void ICACHE_FLASH_ATTR sigmaDeltaDetachPin(uint8_t pin)
+{
+  if (pin < 16) {
+    // set its source to the sigma delta source
+    GPC(pin) &=  ~(1 << GPCS); //SOURCE 0:GPIO_DATA,1:SigmaDelta
+  }
+}
+
+/******************************************************************************
+ * FunctionName : sigmaDeltaIsPinAttached
+ * Description  : query if pin is attached
+ * Parameters   : pin (0..16)
+ * Returns      : bool
+*******************************************************************************/
+bool ICACHE_FLASH_ATTR sigmaDeltaIsPinAttached(uint8_t pin)
+{
+  if (pin < 16) {
+    // set its source to the sigma delta source
+     return (GPC(pin) & (1 << GPCS)); //SOURCE 0:GPIO_DATA,1:SigmaDelta
+  }
+  else
+    return false;
+}
+
+/******************************************************************************
+ * FunctionName : sigmaDeltaSetup
+ * Description  : start the sigma delta generator with the chosen parameters
+ * Parameters   : channel = unused (for compatibility with ESP32), 
+ *                freq : 1220-312500 (lowest frequency in the output signal's spectrum)
+ * Returns      : uint32_t the actual frequency, closest to the input parameter
+*******************************************************************************/
+uint32_t ICACHE_FLASH_ATTR sigmaDeltaSetup(uint8_t channel, uint32_t freq)
+{
+  (void) channel;
+  
+  uint32_t prescaler = ((uint32_t)10000000/(freq*32)) - 1;
+  
+  if(prescaler > 0xFF) {
+      prescaler = 0xFF;
+  }
+  sigmaDeltaEnable();
+  sigmaDeltaSetPrescaler ((uint8_t) prescaler);
+  
+  return 10000000/((prescaler + 1) * 32);
+}
+
+/******************************************************************************
+ * FunctionName : sigmaDeltaWrite
+ * Description  : set the duty cycle for the sigma-delta source
+ * Parameters   : uint8 duty, 0-255, duty cycle = target/256, 
+ *                channel = unused, for compatibility with ESP32
+ * Returns      : none
+*******************************************************************************/
+void ICACHE_FLASH_ATTR sigmaDeltaWrite(uint8_t channel, uint8_t duty)
+{
+  uint32_t reg = GPSD;
+  (void) channel;
+
+  reg = (reg & ~(0xFF << GPSDT)) | ((duty & 0xFF) << GPSDT);
+  GPSD = reg;
+  
+}
+/******************************************************************************
+ * FunctionName : sigmaDeltaRead
+ * Description  : get the duty cycle for the sigma-delta source
+ * Parameters   : channel = unused, for compatibility with ESP32
+ * Returns      : uint8_t duty cycle value 0..255
+*******************************************************************************/
+uint8_t ICACHE_FLASH_ATTR sigmaDeltaRead(uint8_t channel)
+{
+  (void) channel;
+  return (uint8_t)((GPSD >> GPSDT) & 0xFF);
+}
+
+/******************************************************************************
+ * FunctionName : sigmaDeltaSetPrescaler
+ * Description  : set the clock divider for the sigma-delta source
+ * Parameters   : uint8 prescaler, 0-255, divides the 80MHz base clock by this amount
+ * Returns      : none
+*******************************************************************************/
+void ICACHE_FLASH_ATTR sigmaDeltaSetPrescaler(uint8_t prescaler)
+{
+  uint32_t reg = GPSD;
+
+  reg = (reg & ~(0xFF << GPSDP)) | ((prescaler & 0xFF) << GPSDP);
+  GPSD = reg;
+}
+
+/******************************************************************************
+ * FunctionName : sigmaDeltaGetPrescaler
+ * Description  : get the prescaler value from the GPIO_SIGMA_DELTA register
+ * Parameters   : none
+ * Returns      : uint8 prescaler, CLK_DIV , 0-255
+*******************************************************************************/
+uint8_t ICACHE_FLASH_ATTR sigmaDeltaGetPrescaler(void)
+{
+  return (uint8_t)((GPSD >> GPSDP) & 0xFF);
+}
diff --git a/cores/esp8266/sigma_delta.h b/cores/esp8266/sigma_delta.h
index 2e8bdc092f..6792f931cb 100644
--- a/cores/esp8266/sigma_delta.h
+++ b/cores/esp8266/sigma_delta.h
@@ -18,15 +18,55 @@
  License along with this library; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */
+ 
+ /*******************************************************************************
+ * Info Sigma delta module
+
+This module controls the esp8266 internal sigma delta source
+Each pin can be connected to the sigma delta source
+The target duty and frequency can be modified via the register GPIO_SIGMA_DELTA
+
+THE TARGET FREQUENCY IS DEFINED AS:
+
+FREQ = 80,000,000/prescaler * target /256  HZ,     0<target<128
+FREQ = 80,000,000/prescaler * (256-target) /256  HZ,     128<target<256
+target: duty cycle,range 0-255
+prescaler: is a clock divider, range 0-255
+so the target and prescale will both affect the freq.
+CPU_FREQ has no influence on the sigma delta frequency.
+
+Usage :
+1. sigmaDeltaSetup(0,f) : activate the sigma delta source with frequency f and default duty cycle (0)
+2. sigmaDeltaAttachPin(pin), any pin 0..15, TBC if gpio16 supports sigma-delta source
+     This will set the pin to NORMAL output mode (pinMode(pin,OUTPUT))
+3. sigmaDeltaWrite(0,dc) : set the output signal duty cycle, duty cycle = dc/256
+
+*******************************************************************************/
 
 #ifndef SIGMA_DELTA_H
 #define SIGMA_DELTA_H
 
-#include <stdint.h>
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+//channel parameter is unused (only for ESP32 compatibility) freq 1220-312500 duty 0-255
+void        sigmaDeltaEnable(void);
+void        sigmaDeltaDisable(void);
+uint32_t    sigmaDeltaSetup(uint8_t channel, uint32_t freq);
+void        sigmaDeltaWrite(uint8_t channel, uint8_t duty);
+uint8_t     sigmaDeltaRead(uint8_t channel = 0);
+void        sigmaDeltaAttachPin(uint8_t pin, uint8_t channel = 0);
+void        sigmaDeltaDetachPin(uint8_t pin);
+bool        sigmaDeltaIsPinAttached(uint8_t pin);
+
+// alternative way to control the sigma delta generator frequency
+uint8_t     sigmaDeltaGetPrescaler(void);
+void        sigmaDeltaSetPrescaler(uint8_t prescaler);
+
 
-void sigma_delta_close(uint32_t gpio);
-void set_sigma_target(uint8_t target);
-void set_sigma_prescale(uint8_t prescale);
-void set_sigma_duty_312KHz(uint8_t duty);
+#ifdef __cplusplus
+}
+#endif
 
 #endif//SIGMA_DELTA_H
diff --git a/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino b/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
new file mode 100644
index 0000000000..e5286ccb05
--- /dev/null
+++ b/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
@@ -0,0 +1,47 @@
+/* Any copyright is dedicated to the Public Domain. */
+
+#include "sigma_delta.h"
+
+void setup() {
+
+  Serial.begin(115200);
+  pinMode(LED_BUILTIN, OUTPUT); // blinkie & sigma-delta mix
+  uint32_t reqFreq = 1000;
+  uint32_t realFreq;
+  
+  realFreq = sigmaDeltaSetup(0, reqFreq); // chose a low frequency
+
+  Serial.println();
+  Serial.println("Start Sigma Delta Example\n");
+  Serial.printf("Frequency = %u\n", realFreq);
+  
+}
+
+void loop() {
+ 
+  uint8_t duty, iRepeat;
+  
+  Serial.println("Attaching the built in led to the sigma delta source now\n");
+  Serial.printf("Current duty = %i, prescaler = %i\n", sigmaDeltaRead(), sigmaDeltaGetPrescaler());
+  sigmaDeltaAttachPin(LED_BUILTIN);
+  
+  Serial.println("dimming builtin led...\n");
+  for (iRepeat = 0; iRepeat < 10; iRepeat++) {
+    for (duty = 0; duty < 255; duty = duty + 5) {
+      sigmaDeltaWrite(0, duty);
+      delay(10);
+    }
+    
+    for (duty = 255; duty > 0; duty = duty - 5) {
+      sigmaDeltaWrite(0, duty);
+      delay(10);
+    }
+    
+  }
+  Serial.println("detaching builtin led & playing a blinkie\n");
+  sigmaDeltaDetachPin(LED_BUILTIN);
+  for (iRepeat = 0; iRepeat < 20; iRepeat++) {
+    digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));
+    delay(500);
+  } 
+}
diff --git a/sigma_delta.h b/sigma_delta.h
new file mode 100644
index 0000000000..6ed66191d5
--- /dev/null
+++ b/sigma_delta.h
@@ -0,0 +1,72 @@
+/* 
+ sigma_delta.h - esp8266 sigma-delta source
+
+ Copyright (c) 2014 Ivan Grokhotkov. All rights reserved.
+ This file is part of the esp8266 core for Arduino environment.
+ 
+ This library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ This library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with this library; if not, write to the Free Software
+ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+ 
+ /*
+/******************************************************************************
+ * Info Sigma delta module
+
+This module controls the esp8266 internal sigma delta source
+Each pin can be connected to the sigma delta source
+The target duty and frequency can be modified via the register GPIO_SIGMA_DELTA
+
+THE TARGET FREQUENCY IS DEFINED AS:
+
+FREQ = 80,000,000/prescaler * target /256  HZ,     0<target<128
+FREQ = 80,000,000/prescaler * (256-target) /256  HZ,     128<target<256
+target: duty ,0-255
+prescaler: clk_div,0-255
+so the target and prescale will both affect the freq.
+
+Usage :
+1. sigma_delta_enable() : activate the sigma delta source with default prescalar (0) & target (0)
+2. sigma_delta_attachPin(pin), any pin 0..15, TBC if gpio16 supports sigma-delta source
+     This will set the pin to NORMAL output mode (pinMode(pin,OUTPUT))
+3. sigma_delta_setPrescaler(uint8_t) : reduce the output frequencies
+4. sigma_delta_setTarget(uint8_t) : set the output signal duty cycle, duty cycle = target/256
+
+5. sigma_delta_detachPin(pin), this will revert the pin to NORMAL output mode & GPIO source. 
+The sigma delta source remains on until :
+6. sigma_delta_disable()
+
+*******************************************************************************/
+
+#ifndef SIGMA_DELTA_H
+#define SIGMA_DELTA_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+void sigma_delta_enable(void);
+void sigma_delta_disable(void);
+void sigma_delta_attachPin(uint8_t pin);
+void sigma_delta_detachPin(uint8_t pin);
+bool sigma_delta_isPinAttached(uint8_t pin);
+uint8_t sigma_delta_getTarget(void);
+void sigma_delta_setTarget(uint8_t target);
+uint8_t sigma_delta_getPrescaler(void);
+void sigma_delta_setPrescaler(uint8_t prescaler);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif//SIGMA_DELTA_H