The smart Home Comfort Control System that will replace Thermostats old and new

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Home climate control is quickly becoming Internet connected, with Nest’s thermostat at the forefront. While these newly emerging devices are a significant improvement over their predecessors in terms of customizability and user experience, smart thermostat systems are not yet smart enough since they are still wall-mounted.This antiquated legacy means the thermostat is not placed in the most efficient location for a temperature sensor, a heating/cooling actuator or a user interface.

shelºF was born from these inefficiencies as a three part internet connected solution:
- shelºF Sense: hidden temperature sensors to place around the home
- shelºF Act: an actuator to turn on the central fan, heater or air-conditioner
- shelºF Control: a simple app to control it all

With these three components the result is a much simpler and personalized Comfort Control System that allows you to control temperature better than the conventional Thermostat.


shelºF Sense

The first shelºF Sense device, the TempBook, is a small, simple board that is made up of an Electric Imp, a temperature sensor and a power supply.

The Electric Imp imp002 module is a great fit for this device since it has the ability to function in three states: sleep, shallow wake and wake. Sleep is when the imp is not performing any function and goes into a very low power mode (5uA) that it wakes up from after a set amount of time. Shallow wake is when the imp is performing typical microcontroller functions without connecting to the Internet, which is where a lot of the power consumption comes from (40mA). And wake is when the imp is connected to the Internet and ready to send/receive data (80mA). For a device that just measures temperature the imp is ideal since it only needs to be awake to quickly measuring temperature, which results in no battery waste.

The temperature sensor chosen for this device was the Si7021 temperature and humidity sensor. This IC was chosen because it is cheap, small and has a very simple I2C protocol that allows for quick setup. The board is powered by two AAA batteries that offer 3V and up to 1200mAh which was all that was needed for this low power application. This power source is then fed through a reverse voltage protection and under-voltage lockout circuit to ensure the safety of the board as a whole. This is then fed through the Torex XC9128 to produce the necessary 3V for the imp, which was chosen due to its efficiency and ability to save power when the imp is off.

shelºF Act

Most thermostats are designed to connect to four wires, one common wire and one each to control the fan, cooling and heating. Each mode is activated by connecting the common wire to the desired function or functions. Since the first iteration of shel°F is designed only for heating, it has one relay for the fan and one for the heater. I selected the 2-Channel Relay Module by SainSmart which has all the FETS and diodes necessary to drive the relays from the Imp. It is sold by many retailers and can be found for under $3. This module is then just connected to the Electric Imp April Board with 4 wires and the shelºF Act hardware is complete and connected to the Internet. The Electric Imp April Board is a great solution to connect to the Internet since anyone can go online and purchase it, and it works right out of the box with no complex soldering. This simple purchase and setup is very important to convince potential customers that this is not a task for an Electrical Engineer, but anyone who would feel comfortable setting up a normal thermostat.



A wireless thermostat system needs software for sensing, actuating, control and a server to connect everything together. It is clear to see that the first three components are controlled by the shelºF, but the main advantage of using the Electric Imp platform is that there is no need for an external server for the last component. Each device has an agent that it can communicate with, which in turn acts as a small server that can store data and take requests.The system model outlined below shows the connections between the app and the two imp devices. The App gets all of the necessary information from the Master Agent using http requests, never talking to the Sensor Agent. The Master Agent then gets all of the sensors’ states from data pushed by the Sensor Agents, and stores it in a table. Based on the sensor state and the targets set by the app the Agent then switches the relays accordingly.

shelºF Sense

The agent code for Sense is quite simple. When the system is configured it is passed the URL of the Master Agent. Whenever it receives a reading from the device it sends the temperature to the Master Agent via a HTTPS Post.

The Imp device code performs temperature/humidity measurement using the Si7021 sensor class and sends this information and its battery level to it's agent. In order to save battery, it attempts to deep...

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  • 1 × IMP001 Electric Imp Chip (SD Card)
  • 1 × April Board Electric Imp Commercial Board
  • 1 × SainSmart 2 Channel Relay Module Relay Module
  • 1 × IMP002 Electric Imp Chip (PCB Module)
  • 1 × TempBook Board Electric Imp Custom Board

View all 30 components

  • Moving Forward

    Juan Albanell08/11/2014 at 09:19 0 comments

    The software and hardware are ready and working, but there are still improvements that need to be made before this product could be fully marketable. The first big focus would be to improve the target temperature algorithm to make it smarter over time and account for the climate outside the home and the season to have both cooling and heating. Another part of the improved algorithm would involve adding the option to schedule temperature settings, from daily patterns to monthly events. A more complex feature to add would be to change room priorities based on the users’ locations in the house. This could be done by adding a bluetooth chip to the shelºF Sense and make it perform the functions of an iBeacon or with a low power PIR motion sensor. With those improvements to the current project the shelºF system would be able to provide a superior offering at a better price than the current competition. The table below shows that at 1 unit pricing the cost is under $100, where the Nest is $250, and the costs can still be halved if the components are purchased in bulk. Most importantly it would move the industry in the right direction by making the Internet connected thermostat truly wireless.

    shelºF Act
    shelºF Sense (TempBook)
    April Board$7PCB$2
    Relay Board$3Power Supply$2
    Enclosure$2Temp Sensor$2
    Wall USB Power$5BLE$8
    Total @ 1 unit$42Total @ 1 unit$40

  • Demo Video

    Juan Albanell08/10/2014 at 10:24 0 comments

    So everything is working properly and I made a demo video to show it. It's short and simple to show how easy it is to use shelºF. The lightbulb was the easiest way to simulate a heater and it did the job quite well. So what you see is the actual system with temperature changing! 
    I will probably make a longer video later showing all the app details and going over the TempBook board.

  • The Build Process

    Juan Albanell08/09/2014 at 23:58 0 comments

    As can be seen in the build instructions, since everything I designed and coded is open source, it is easy to get shel°F setup and running in no time. But during the build process I experienced a few difficulties that I thought would be useful to share:

    • The Si7021 sensor comes in a tiny hard to solder package. A heat gun could be used to put it down and make things easier but it could tamper with the sensor according o the datasheet. My solution was to put a little bit of solder on the center pad and slide the sensor into position making sure it is connected to the center and not moving. Then, heating the sides of each pin on the chip and the pad, you add a little bit of solder to create the connection.
    • The Si7021 has a sticker on the top that needs to be keep on particles that could make the sensor malfunction. I accidentally removed the sticker on one of my sensors at the start and the readings were pretty much the same as a sensor with the sticker. That said in the long run things will probably become more inconsistent so since there is no harm, keep the sticker.
    • The book is pretty simple to hollow out if you follow the link to the instructions closely. One thing to note is that if you cut out the top of the book to make the sensor pop out it is best if that is not the only way the heat from the board can go. To prevent the creation of a chimney, you can either block the exit by not cutting out the edge and having the sensor slide out through a small opening or you can create another larger chimney on the side or bottom. I didn't do either and the results have been fine, but it doesn't hurt to make the design more robust.

  • Origin of the Design

    Juan Albanell08/09/2014 at 00:26 0 comments

    The original idea, to replace the wall-mounted thermostat system, was born in a recent Electric Imp Hackathon. Later on this concept would develop into the shelºF three part solution consisting of an actuator, sensor and controller. But the design of the project was decided very early on, especially regarding the sensor and the controller.
    The sensor had to blend into the home, the issue with the wall-mounted unit is that no matter how pretty you make it, like Nest's product, it still can clash with the overall design of your home. The first solution, which eventually led to the TempBook board, was to put the sensor in a hollowed-out book. This is an item that is abundant in most homes and therefore goes by unnoticed, and it can be built very easily (tutorial I used). Future solutions would involve other hidden, easy to set up objects, such as a plant pot or a picture frame.
    The controller had to be very simple and intuitive, while breaking with the original thermostat controls. The resulting design was a comfort-based system, where the user choses if they feel cold, cool, ok, warm or hot. While this is not the conventional system it gets rid of the confusing numbers that no one needs to know, since all that matters is how you feel.

View all 4 project logs

  • 1
    Step 1

    Starting with the shelºF Act unit, connect the April Board and the 2 Channel Relay Module by wiring VCC to the imp's VIN, GND to the imp's GND, IN2 to the imp's Pin1 and IN1 to the imp's Pin2

  • 2
    Step 2

    For the shelºF Sense TempBook board, solder all the components on the PCB as specified by the schematics

  • 3
    Step 3

    Connect the heating, cooling and ground wires to the relays and power the shelºF Act unit using the usb port.

View all 6 instructions

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