diff --git a/sensors/builder.cpp b/sensors/builder.cpp
new file mode 100644
index 0000000..2786141
--- /dev/null
+++ b/sensors/builder.cpp
@@ -0,0 +1,153 @@
+/**
+ * Copyright 2017 Google Inc.
+ *
+ * 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 <iostream>
+
+/* Configuration. */
+#include "conf.hpp"
+
+#include "dbus/dbuspassive.hpp"
+#include "interfaces.hpp"
+#include "notimpl/readonly.hpp"
+#include "notimpl/writeonly.hpp"
+#include "sensors/builder.hpp"
+#include "sensors/manager.hpp"
+#include "sensors/host.hpp"
+#include "sensors/pluggable.hpp"
+#include "sysfs/sysfsread.hpp"
+#include "sysfs/sysfswrite.hpp"
+#include "util.hpp"
+
+static constexpr bool deferSignals = true;
+
+std::shared_ptr<SensorManager> BuildSensors(
+    const std::map<std::string, struct sensor>& config)
+{
+    auto mgmr = std::make_shared<SensorManager>();
+    auto& HostSensorBus = mgmr->getHostBus();
+    auto& PassiveListeningBus = mgmr->getPassiveBus();
+
+    for (auto& it : config)
+    {
+        std::unique_ptr<ReadInterface> ri;
+        std::unique_ptr<WriteInterface> wi;
+
+        std::string name = it.first;
+        const struct sensor* info = &it.second;
+
+        std::cerr << "Sensor: " << name << " " << info->type << " ";
+        std::cerr << info->readpath << " " << info->writepath << "\n";
+
+        IOInterfaceType rtype = GetReadInterfaceType(info->readpath);
+        IOInterfaceType wtype = GetWriteInterfaceType(info->writepath);
+
+        // fan sensors can be ready any way and written others.
+        // fan sensors are the only sensors this is designed to write.
+        // Nothing here should be write-only, although, in theory a fan could be.
+        // I'm just not sure how that would fit together.
+        // TODO(venture): It should check with the ObjectMapper to check if
+        // that sensor exists on the Dbus.
+        switch (rtype)
+        {
+            case IOInterfaceType::DBUSPASSIVE:
+                ri = std::make_unique<DbusPassive>(
+                         PassiveListeningBus,
+                         info->type,
+                         name);
+                break;
+            case IOInterfaceType::EXTERNAL:
+                // These are a special case for read-only.
+                break;
+            case IOInterfaceType::SYSFS:
+                ri = std::make_unique<SysFsRead>(info->readpath);
+                break;
+            default:
+                ri = std::make_unique<WriteOnly>();
+                break;
+        }
+
+        if (info->type == "fan")
+        {
+            switch (wtype)
+            {
+                case IOInterfaceType::SYSFS:
+                    if (info->max > 0)
+                    {
+                        wi = std::make_unique<SysFsWritePercent>(
+                                 info->writepath,
+                                 info->min,
+                                 info->max);
+                    }
+                    else
+                    {
+                        wi = std::make_unique<SysFsWrite>(
+                                 info->writepath,
+                                 info->min,
+                                 info->max);
+                    }
+
+                    break;
+                default:
+                    wi = std::make_unique<ReadOnlyNoExcept>();
+                    break;
+            }
+
+            auto sensor = std::make_unique<PluggableSensor>(
+                              name,
+                              info->timeout,
+                              std::move(ri),
+                              std::move(wi));
+            mgmr->addSensor(info->type, name, std::move(sensor));
+        }
+        else if (info->type == "temp" || info->type == "margin")
+        {
+            // These sensors are read-only, but only for this application
+            // which only writes to fan sensors.
+            std::cerr << info->type << " readpath: " << info->readpath << "\n";
+
+            if (IOInterfaceType::EXTERNAL == rtype)
+            {
+                std::cerr << "Creating HostSensor: " << name
+                          << " path: " << info->readpath << "\n";
+
+                /*
+                 * The reason we handle this as a HostSensor is because it's
+                 * not quite pluggable; but maybe it could be.
+                 */
+                auto sensor = HostSensor::CreateTemp(
+                                  name,
+                                  info->timeout,
+                                  HostSensorBus,
+                                  info->readpath.c_str(),
+                                  deferSignals);
+                mgmr->addSensor(info->type, name, std::move(sensor));
+            }
+            else
+            {
+                wi = std::make_unique<ReadOnlyNoExcept>();
+                auto sensor = std::make_unique<PluggableSensor>(
+                                  name,
+                                  info->timeout,
+                                  std::move(ri),
+                                  std::move(wi));
+                mgmr->addSensor(info->type, name, std::move(sensor));
+            }
+        }
+    }
+
+    return mgmr;
+}
+