diff --git a/libraries/ADG731/.arduino-ci.yml b/libraries/ADG731/.arduino-ci.yml
new file mode 100644
index 00000000..10c0e10b
--- /dev/null
+++ b/libraries/ADG731/.arduino-ci.yml
@@ -0,0 +1,28 @@
+platforms:
+  rpipico:
+    board: rp2040:rp2040:rpipico
+    package: rp2040:rp2040
+    gcc:
+      features:
+      defines:
+        - ARDUINO_ARCH_RP2040
+      warnings:
+      flags:
+
+packages:
+  rp2040:rp2040:
+    url: https://github.com/earlephilhower/arduino-pico/releases/download/global/package_rp2040_index.json
+
+compile:
+  # Choosing to run compilation tests on 2 different Arduino platforms
+  platforms:
+    - uno
+    # - due
+    # - zero
+    # - leonardo
+    - m4
+    - esp32
+    # - esp8266
+    # - mega2560
+    - rpipico
+
diff --git a/libraries/ADG731/.github/FUNDING.yml b/libraries/ADG731/.github/FUNDING.yml
new file mode 100644
index 00000000..90d9ab4c
--- /dev/null
+++ b/libraries/ADG731/.github/FUNDING.yml
@@ -0,0 +1,4 @@
+# These are supported funding model platforms
+
+github: RobTillaart
+
diff --git a/libraries/ADG731/.github/workflows/arduino-lint.yml b/libraries/ADG731/.github/workflows/arduino-lint.yml
new file mode 100644
index 00000000..8a26f14a
--- /dev/null
+++ b/libraries/ADG731/.github/workflows/arduino-lint.yml
@@ -0,0 +1,13 @@
+
+name: Arduino-lint
+
+on: [push, pull_request]
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: arduino/arduino-lint-action@v1
+        with:
+          library-manager: update
+          compliance: strict
diff --git a/libraries/ADG731/.github/workflows/arduino_test_runner.yml b/libraries/ADG731/.github/workflows/arduino_test_runner.yml
new file mode 100644
index 00000000..a1090a68
--- /dev/null
+++ b/libraries/ADG731/.github/workflows/arduino_test_runner.yml
@@ -0,0 +1,17 @@
+---
+name: Arduino CI
+
+on: [push, pull_request]
+
+jobs:
+  runTest:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v3
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: 2.6
+      - run: |
+          gem install arduino_ci
+          arduino_ci.rb
\ No newline at end of file
diff --git a/libraries/ADG731/.github/workflows/jsoncheck.yml b/libraries/ADG731/.github/workflows/jsoncheck.yml
new file mode 100644
index 00000000..37a11298
--- /dev/null
+++ b/libraries/ADG731/.github/workflows/jsoncheck.yml
@@ -0,0 +1,18 @@
+name: JSON check
+
+on:
+  push:
+    paths:
+      - '**.json'
+  pull_request:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: json-syntax-check
+        uses: limitusus/json-syntax-check@v1
+        with:
+          pattern: "\\.json$"
+
diff --git a/libraries/ADG731/ADG731.h b/libraries/ADG731/ADG731.h
new file mode 100644
index 00000000..1c6705ff
--- /dev/null
+++ b/libraries/ADG731/ADG731.h
@@ -0,0 +1,88 @@
+#pragma once
+//
+//    FILE: ADG731.h
+//  AUTHOR: Rob Tillaart
+//    DATE: 2023-07-24
+// VERSION: 0.1.0
+// PURPOSE: Arduino library for ADG731 - 32 to 1 channel multiplexer
+//     URL: https://github.com/RobTillaart/ADG731
+
+
+#include "Arduino.h"
+
+#define ADG731_LIB_VERSION         (F("0.1.0"))
+
+#define ADG731_ALLOFF              0x80
+
+
+class ADG731
+{
+public:
+  explicit ADG731(uint8_t clockPin, uint8_t dataPin, uint8_t syncPin)
+  {
+    _clockPin = clockPin;
+    _dataPin  = dataPin;
+    _syncPin  = syncPin;
+
+    pinMode(_clockPin, OUTPUT);
+    pinMode(_dataPin, OUTPUT);
+    pinMode(_syncPin, OUTPUT);
+
+    digitalWrite(_clockPin, HIGH);
+    digitalWrite(_dataPin, HIGH);
+    digitalWrite(_syncPin, HIGH);
+
+    //  default all off.
+    _channel = ADG731_ALLOFF;
+  }
+
+
+  void setChannel(uint8_t channel)
+  {
+    _channel = channel & 0x0F;
+    write(_channel);
+  }
+
+
+  uint8_t getChannel()
+  {
+    return _channel;
+  }
+
+
+  uint8_t channelCount()
+  {
+    return 32;
+  }
+
+
+  void allOff()
+  {
+    _channel = ADG731_ALLOFF;
+    write(_channel);
+  }
+
+
+private:
+  void write(uint8_t data)
+  {
+    digitalWrite(_syncPin, LOW);
+    for (int i = 0; i < 8; i++)
+    {
+      //  CLOCK max 30 MHz.
+      digitalWrite(_clockPin, HIGH);
+      digitalWrite(_dataPin, (data & 0x80) > 0);
+      data <<= 1;
+      digitalWrite(_clockPin, LOW);
+    }
+    digitalWrite(_syncPin, HIGH);
+  }
+
+  uint8_t  _clockPin;
+  uint8_t  _dataPin;
+  uint8_t  _syncPin;
+  uint8_t  _channel;
+};
+
+
+//  -- END OF FILE --
diff --git a/libraries/ADG731/CHANGELOG.md b/libraries/ADG731/CHANGELOG.md
new file mode 100644
index 00000000..522aed1c
--- /dev/null
+++ b/libraries/ADG731/CHANGELOG.md
@@ -0,0 +1,10 @@
+# Change Log ADG731
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](http://keepachangelog.com/)
+and this project adheres to [Semantic Versioning](http://semver.org/).
+
+
+## [0.1.0] - 2023-07-24
+- initial version
diff --git a/libraries/ADG731/LICENSE b/libraries/ADG731/LICENSE
new file mode 100644
index 00000000..16ef1551
--- /dev/null
+++ b/libraries/ADG731/LICENSE
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2023-2023 Rob Tillaart
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/libraries/ADG731/README.md b/libraries/ADG731/README.md
new file mode 100644
index 00000000..568d2c8a
--- /dev/null
+++ b/libraries/ADG731/README.md
@@ -0,0 +1,77 @@
+
+[![Arduino CI](https://github.com/RobTillaart/ADG731/workflows/Arduino%20CI/badge.svg)](https://github.com/marketplace/actions/arduino_ci)
+[![Arduino-lint](https://github.com/RobTillaart/ADG731/actions/workflows/arduino-lint.yml/badge.svg)](https://github.com/RobTillaart/ADG731/actions/workflows/arduino-lint.yml)
+[![JSON check](https://github.com/RobTillaart/ADG731/actions/workflows/jsoncheck.yml/badge.svg)](https://github.com/RobTillaart/ADG731/actions/workflows/jsoncheck.yml)
+[![License: MIT](https://img.shields.io/badge/license-MIT-green.svg)](https://github.com/RobTillaart/ADG731/blob/master/LICENSE)
+[![GitHub release](https://img.shields.io/github/release/RobTillaart/ADG731.svg?maxAge=3600)](https://github.com/RobTillaart/ADG731/releases)
+
+
+# ADG731
+
+Arduino library for ADG731 - 32 to 1 channel multiplexer.
+
+
+## Description
+
+**Experimental**
+
+ADG731 is an Arduino class that controls a 1 x 32 multiplexer over a SPI
+like interface.
+Only one of the 32 channels can be connected at the same time.
+The library also support to set them all off (17th state).
+
+This library can be used to connect 32 analog devices to one analog port.
+
+On power-up, all switches are in the OFF state.
+
+This library can be used e.g. to connect 32 analog devices to 
+one analog port, or to select between 32 DHT22 sensors.
+
+Not tests with hardware have been done yet, so use with care.
+Feedback welcome!
+
+
+TODO insert picture.
+
+
+#### Related
+
+- https://github.com/RobTillaart/HC4051 (1x8 mux)
+- https://github.com/RobTillaart/HC4052 (2x8 mux)
+- https://github.com/RobTillaart/HC4053 (3x2 mux)
+- https://github.com/RobTillaart/HC4067 (1x16 mux)
+- https://github.com/RobTillaart/ADG725 (2x16 mux)
+- https://github.com/RobTillaart/ADG731 (1x32 mux)
+
+
+## Interface
+
+```cpp
+#include "ADG731.h"
+```
+
+- **ADG731(uint8_t clockPin, uint8_t dataPin, uint8_t syncPin)** constructor.
+- **void setChannel(uint8_t channel)** set the current channel.
+Valid values for channel are 0..31.
+- **uint8_t getChannel()** get last set channel == 0..31 or ADG731_ALLOFF.
+- **uint8_t channelCount()** returns 32 for ADG731.
+
+
+## Future
+
+#### Must
+
+- improve documentation
+- test with hardware
+
+#### Should
+
+- add examples
+- check performance
+
+#### Could
+
+
+#### Wont
+
+
diff --git a/libraries/ADG731/examples/ADG731_demo/ADG731_demo.ino b/libraries/ADG731/examples/ADG731_demo/ADG731_demo.ino
new file mode 100644
index 00000000..204a23ea
--- /dev/null
+++ b/libraries/ADG731/examples/ADG731_demo/ADG731_demo.ino
@@ -0,0 +1,52 @@
+//
+//    FILE: ADG731_demo.ino
+//  AUTHOR: Rob Tillaart
+// PURPOSE: minimal sketch
+//     URL: https://github.com/RobTillaart/ADG731
+
+
+#include "ADG731.h"
+
+
+ADG731 ADG(10, 11, 12);
+
+uint32_t start, stop;
+
+void setup()
+{
+  Serial.begin(115200);
+  Serial.print("ADG731_LIB_VERSION: ");
+  Serial.println(ADG731_LIB_VERSION);
+  delay(100);
+  
+  start = micros();
+  ADG.setChannel(0);
+  stop = micros();
+  Serial.print("Time:\t");
+  Serial.println(stop - start);
+  delay(100);
+
+  start = micros();
+  ADG.setChannel(1);
+  stop = micros();
+  Serial.print("Time:\t");
+  Serial.println(stop - start);
+  delay(100);
+}
+
+
+void loop()
+{
+  for (int ch = 0; ch < 32; ch++)
+  {
+    ADG.setChannel(ch);
+
+    Serial.print(ch);
+    Serial.print("\t");
+    Serial.println(ADG.getChannel());
+    delay(1000);
+  }
+}
+
+
+//  -- END OF FILE --
diff --git a/libraries/ADG731/keywords.txt b/libraries/ADG731/keywords.txt
new file mode 100644
index 00000000..1ca6222f
--- /dev/null
+++ b/libraries/ADG731/keywords.txt
@@ -0,0 +1,17 @@
+# Syntax Colouring Map For ADG731
+
+# Data types (KEYWORD1)
+ADG731	KEYWORD1
+
+
+# Methods and Functions (KEYWORD2)
+setChannel	KEYWORD2
+setChannel	KEYWORD2
+getChannel	KEYWORD2
+channelCount	KEYWORD2
+
+
+# Constants (LITERAL1)
+ADG731_LIB_VERSION	LITERAL1
+
+ADG731_ALLOFF	LITERAL1
diff --git a/libraries/ADG731/library.json b/libraries/ADG731/library.json
new file mode 100644
index 00000000..cacd4823
--- /dev/null
+++ b/libraries/ADG731/library.json
@@ -0,0 +1,23 @@
+{
+  "name": "ADG731",
+  "keywords": "ADG731,32,1, multiplexer, MUX",
+  "description": "Arduino library for ADG731 - 32 to 1 channel multiplexer.",
+  "authors":
+  [
+    {
+      "name": "Rob Tillaart",
+      "email": "Rob.Tillaart@gmail.com",
+      "maintainer": true
+    }
+  ],
+  "repository":
+  {
+    "type": "git",
+    "url": "https://github.com/RobTillaart/ADG731"
+  },
+  "version": "0.1.0",
+  "license": "MIT",
+  "frameworks": "*",
+  "platforms": "*",
+  "headers": "ADG731.h"
+}
diff --git a/libraries/ADG731/library.properties b/libraries/ADG731/library.properties
new file mode 100644
index 00000000..2bb54416
--- /dev/null
+++ b/libraries/ADG731/library.properties
@@ -0,0 +1,11 @@
+name=ADG731
+version=0.1.0
+author=Rob Tillaart <rob.tillaart@gmail.com>
+maintainer=Rob Tillaart <rob.tillaart@gmail.com>
+sentence=Arduino library for ADG731 - 32 to 1 channel multiplexer.
+paragraph= 
+category=Signal Input/Output
+url=https://github.com/RobTillaart/ADG731
+architectures=*
+includes=ADG731.h
+depends=
diff --git a/libraries/ADG731/test/unit_test_001.cpp b/libraries/ADG731/test/unit_test_001.cpp
new file mode 100644
index 00000000..a3f6ba90
--- /dev/null
+++ b/libraries/ADG731/test/unit_test_001.cpp
@@ -0,0 +1,80 @@
+//
+//    FILE: unit_test_001.cpp
+//  AUTHOR: Rob Tillaart
+//    DATE: 2023-07-24
+// PURPOSE: unit tests for the ADG731 library
+//          https://github.com/RobTillaart/ADG731
+//          https://github.com/Arduino-CI/arduino_ci/blob/master/REFERENCE.md
+//
+
+// supported assertions
+// ----------------------------
+// assertEqual(expected, actual)
+// assertNotEqual(expected, actual)
+// assertLess(expected, actual)
+// assertMore(expected, actual)
+// assertLessOrEqual(expected, actual)
+// assertMoreOrEqual(expected, actual)
+// assertTrue(actual)
+// assertFalse(actual)
+// assertNull(actual)
+
+#include <ArduinoUnitTests.h>
+
+#include "Arduino.h"
+#include "ADG731.h"
+
+
+unittest_setup()
+{
+  fprintf(stderr, "ADG731_LIB_VERSION: %s\n", (char *) ADG731_LIB_VERSION);
+}
+
+
+unittest_teardown()
+{
+}
+
+
+unittest(test_constructor)
+{
+  ADG731 ADG(10, 11, 12);
+
+  assertEqual(32, ADG.channelCount());
+  assertEqual(ADG731_ALLOFF, ADG.getChannel());
+}
+
+
+unittest(test_constants)
+{
+  assertEqual(0x80, ADG731_ALLOFF );
+}
+
+
+unittest(test_allOff)
+{
+  ADG731 ADG(10, 11, 12);
+
+  ADG.setChannel(13);
+  ADG.allOff();
+  assertEqual(ADG731_ALLOFF, ADG.getChannel());
+}
+
+
+unittest(test_channel)
+{
+  ADG731 ADG(10, 11, 12);
+
+  for (int ch = 0; ch < 16; ch++)
+  {
+    ADG.setChannel(ch);
+    assertEqual(ch, ADG.getChannel());
+  }
+}
+
+
+unittest_main()
+
+
+//  -- END OF FILE --
+