diff --git a/sensors/src/TachSensor.cpp b/sensors/src/TachSensor.cpp
new file mode 100644
index 0000000..91f0545
--- /dev/null
+++ b/sensors/src/TachSensor.cpp
@@ -0,0 +1,312 @@
+/*
+// Copyright (c) 2018 Intel Corporation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+*/
+
+#include <unistd.h>
+
+#include <TachSensor.hpp>
+#include <Utils.hpp>
+#include <boost/algorithm/string/predicate.hpp>
+#include <boost/algorithm/string/replace.hpp>
+#include <boost/date_time/posix_time/posix_time.hpp>
+#include <iostream>
+#include <limits>
+#include <sdbusplus/asio/connection.hpp>
+#include <sdbusplus/asio/object_server.hpp>
+#include <string>
+
+static constexpr unsigned int PWM_POLL_MS = 500;
+static constexpr size_t WARN_AFTER_ERROR_COUNT = 10;
+
+TachSensor::TachSensor(const std::string &path,
+                       sdbusplus::asio::object_server &objectServer,
+                       std::shared_ptr<sdbusplus::asio::connection> &conn,
+                       boost::asio::io_service &io, const std::string &fanName,
+                       std::vector<thresholds::Threshold> &&_thresholds,
+                       const std::string &sensorConfiguration) :
+    path(path),
+    objServer(objectServer), dbusConnection(conn),
+    name(boost::replace_all_copy(fanName, " ", "_")),
+    configuration(sensorConfiguration), thresholds(std::move(_thresholds)),
+    sensor_interface(objectServer.add_interface(
+        "/xyz/openbmc_project/sensors/fan_tach/" + name,
+        "xyz.openbmc_project.Sensor.Value")),
+    input_dev(io, open(path.c_str(), O_RDONLY)), wait_timer(io),
+    value(std::numeric_limits<double>::quiet_NaN()), err_count(0),
+    // todo, get these from config
+    max_value(25000), min_value(0)
+{
+    if (thresholds::HasWarningInterface(thresholds))
+    {
+        threshold_interface_warning = objectServer.add_interface(
+            "/xyz/openbmc_project/sensors/fan_tach/" + name,
+            "xyz.openbmc_project.Sensor.Threshold.Warning");
+    }
+    if (thresholds::HasCriticalInterface(thresholds))
+    {
+        threshold_interface_critical = objectServer.add_interface(
+            "/xyz/openbmc_project/sensors/fan_tach/" + name,
+            "xyz.openbmc_project.Sensor.Threshold.Critical");
+    }
+    set_initial_properties(conn);
+    isPowerOn(dbusConnection); // first call initializes
+    setup_read();
+}
+
+TachSensor::~TachSensor()
+{
+    // close the input dev to cancel async operations
+    input_dev.close();
+    wait_timer.cancel();
+    objServer.remove_interface(threshold_interface_warning);
+    objServer.remove_interface(threshold_interface_critical);
+    objServer.remove_interface(sensor_interface);
+}
+
+void TachSensor::setup_read(void)
+{
+    boost::asio::async_read_until(
+        input_dev, read_buf, '\n',
+        [&](const boost::system::error_code &ec,
+            std::size_t /*bytes_transfered*/) { handle_response(ec); });
+}
+
+void TachSensor::handle_response(const boost::system::error_code &err)
+{
+    if (err == boost::system::errc::bad_file_descriptor)
+    {
+        return; // we're being destroyed
+    }
+    std::istream response_stream(&read_buf);
+    if (!err)
+    {
+        std::string response;
+        try
+        {
+            std::getline(response_stream, response);
+            float nvalue = std::stof(response);
+            response_stream.clear();
+            if (nvalue != value)
+            {
+                update_value(nvalue);
+            }
+            err_count = 0;
+        }
+        catch (const std::invalid_argument &)
+        {
+            err_count++;
+        }
+    }
+    else
+    {
+
+        err_count++;
+    }
+    // only send value update once
+    if (err_count == WARN_AFTER_ERROR_COUNT)
+    {
+        // only an error if power is on
+        if (isPowerOn(dbusConnection))
+        {
+            std::cerr << "Failure to read sensor " << name << " at " << path
+                      << "\n";
+            update_value(0);
+        }
+        else
+        {
+            err_count = 0; // check power again in 10 cycles
+            sensor_interface->set_property(
+                "Value", std::numeric_limits<double>::quiet_NaN());
+        }
+    }
+    response_stream.clear();
+    input_dev.close();
+    int fd = open(path.c_str(), O_RDONLY);
+    if (fd <= 0)
+    {
+        return; // we're no longer valid
+    }
+    input_dev.assign(fd);
+    wait_timer.expires_from_now(boost::posix_time::milliseconds(PWM_POLL_MS));
+    wait_timer.async_wait([&](const boost::system::error_code &ec) {
+        if (ec == boost::asio::error::operation_aborted)
+        {
+            return; // we're being canceled
+        }
+        setup_read();
+    });
+}
+
+void TachSensor::check_thresholds(void)
+{
+    if (thresholds.empty())
+        return;
+    for (auto &threshold : thresholds)
+    {
+        if (threshold.direction == thresholds::Direction::HIGH)
+        {
+            if (value > threshold.value)
+            {
+                assert_thresholds(threshold.level, threshold.direction, true);
+            }
+            else
+            {
+                assert_thresholds(threshold.level, threshold.direction, false);
+            }
+        }
+        else
+        {
+            if (value < threshold.value)
+            {
+                assert_thresholds(threshold.level, threshold.direction, true);
+            }
+            else
+            {
+                assert_thresholds(threshold.level, threshold.direction, false);
+            }
+        }
+    }
+}
+
+void TachSensor::update_value(const double &new_value)
+{
+    sensor_interface->set_property("Value", new_value);
+    value = new_value;
+    check_thresholds();
+}
+
+void TachSensor::assert_thresholds(thresholds::Level level,
+                                   thresholds::Direction direction, bool assert)
+{
+    std::string property;
+    std::shared_ptr<sdbusplus::asio::dbus_interface> interface;
+    if (level == thresholds::Level::WARNING &&
+        direction == thresholds::Direction::HIGH)
+    {
+        property = "WarningAlarmHigh";
+        interface = threshold_interface_warning;
+    }
+    else if (level == thresholds::Level::WARNING &&
+             direction == thresholds::Direction::LOW)
+    {
+        property = "WarningAlarmLow";
+        interface = threshold_interface_warning;
+    }
+    else if (level == thresholds::Level::CRITICAL &&
+             direction == thresholds::Direction::HIGH)
+    {
+        property = "CriticalAlarmHigh";
+        interface = threshold_interface_critical;
+    }
+    else if (level == thresholds::Level::CRITICAL &&
+             direction == thresholds::Direction::LOW)
+    {
+        property = "CriticalAlarmLow";
+        interface = threshold_interface_critical;
+    }
+    else
+    {
+        std::cerr << "Unknown threshold, level " << level << "direction "
+                  << direction << "\n";
+        return;
+    }
+    if (!interface)
+    {
+        std::cout << "trying to set uninitialized interface\n";
+        return;
+    }
+    interface->set_property(property, assert);
+}
+
+void TachSensor::set_initial_properties(
+    std::shared_ptr<sdbusplus::asio::connection> &conn)
+{
+    // todo, get max and min from configuration
+    sensor_interface->register_property("MaxValue", max_value);
+    sensor_interface->register_property("MinValue", min_value);
+    sensor_interface->register_property("Value", value);
+
+    for (auto &threshold : thresholds)
+    {
+        std::shared_ptr<sdbusplus::asio::dbus_interface> iface;
+        std::string level;
+        std::string alarm;
+        if (threshold.level == thresholds::Level::CRITICAL)
+        {
+            iface = threshold_interface_critical;
+            if (threshold.direction == thresholds::Direction::HIGH)
+            {
+                level = "CriticalHigh";
+                alarm = "CriticalAlarmHigh";
+            }
+            else
+            {
+                level = "CriticalLow";
+                alarm = "CriticalAlarmLow";
+            }
+        }
+        else if (threshold.level == thresholds::Level::WARNING)
+        {
+            iface = threshold_interface_warning;
+            if (threshold.direction == thresholds::Direction::HIGH)
+            {
+                level = "WarningHigh";
+                alarm = "WarningAlarmHigh";
+            }
+            else
+            {
+                level = "WarningLow";
+                alarm = "WarningAlarmLow";
+            }
+        }
+        else
+        {
+            std::cerr << "Unknown threshold level" << threshold.level << "\n";
+            continue;
+        }
+        if (!iface)
+        {
+            std::cout << "trying to set uninitialized interface\n";
+            continue;
+        }
+        iface->register_property(
+            level, threshold.value,
+            [&](const double &request, double &oldValue) {
+                oldValue = request; // todo, just let the config do this?
+                threshold.value = request;
+                thresholds::persistThreshold(
+                    configuration,
+                    "xyz.openbmc_project.Configuration.AspeedFan", threshold,
+                    conn);
+                return 1;
+            });
+        iface->register_property(alarm, false);
+    }
+    if (!sensor_interface->initialize())
+    {
+        std::cerr << "error initializing value interface\n";
+    }
+    if (threshold_interface_warning &&
+        !threshold_interface_warning->initialize())
+    {
+        std::cerr << "error initializing warning threshold interface\n";
+    }
+
+    if (threshold_interface_critical &&
+        !threshold_interface_critical->initialize())
+    {
+        std::cerr << "error initializing critical threshold interface\n";
+    }
+}