An Arduino Thermostat

I started this project to create a thermostat which could be controlled from the internet with the following features:

• REST API
• one unit connected to the CV and a unit to control the thermostat
• both units communicating via RF
• have a program for every day of the week with up to 4 time intervals to set a temperature
• be able to temporarily change a temperature for a time interval
• holiday mode, set a specific temperature which will be held until the mode is disabled
• Optional: iOS notifications via Prowl when CV is turned on and off

The FrankenStat conists of 2 arduino's. The first is the MCP, which has the controls, display and the logic. The 2nd Arduino is called BIT and controls the CV burner. Both Arduino's communicate through a 433MHz RF link.

Parts

• 2x Atmega328 based Arduino
• 2x MCP9701 Thermistor
• Hitachi HD44780 compatible LCD screen with I2C interface adapter
• DS1307 RTC
• 2x Buttons
• 433 MHz RF receiver
• 433 MHz RF transmitter
• LED
• Relay

Before compiling copy include/prowl.h-example to include/prowl.h and insert your Prowl API key (make one on the Prowl site, if you don't already have one).

Building

I use the Arduino makefile, as I hate the Arduino IDE. This should work on Linux and Mac OS X.

git clone https://github.com/sudar/Arduino-Makefile.git
ln -s Arduino-Makefile/arduino-mk
git clone https://github.com/arnoudj/FrankenStat.git
cd FrankenStat
cp include/prowl.h-example include/prowl.h # and change the API key
cd mcp
vi Makefile # and change the device name for your arduino
make upload
cd ../bit
vi Makefile # and change the device name for your arduino
make upload

Schematic

TODO: Schematic is outdated, needs an update.

Sensor Accuracy

I noticed that the temerature would go up, when the LED was turned on by about 0.25 degrees. Measuring the voltage showed a small drop in voltage. This was solved by using the 3.3V power, and hooking the 3.3V power to the AREF pin. See the sensor guide on Adafruit.

API

To read the status and control the temperature the following URL's can be used:

All API calls return a JSON with the target temperature, current temperature, status of the CV and current mode.

{
  "target": 21,
  "current": 21.15,
  "burner": false,
  "mode": 0
}

/

Returns the status of the thermostat.

/up

Increase the target temperature. If the mode is set to auto, then mode will be set to temp.

/down

Decrease the target temperature. If the mode is set to auto, then mode will be set to temp.

/mode/MODE[/16]

TODO: Implement

Set the operating mode. Modes can be:

0: Automatic
1: Temporary
2: Holiday

/time/HH:MM

TODO: Implement

Set the time.

TODO's

MCP

• Store the schedule in EEPROM
• API to manage schedule
• Add LDR to detect if light is on or not, no use heating when no-one is home
• Design PCB
• Make a nice enclosure
• Set time using NTP or API call
• API for setting the mode
• Code refactoring, it's ugly and unreadable ;)

BIT

• Add a temperature sensor to BIT and make it use this sensor to set the temperature to a save setting when no message has been received from the MCP for a specific time.
• Design PCB
• Make a nice enclosure

Useful URL's

• EtherCard Examples
• Open Energy Monitoring: Nice example on how to use the EtherCard library.
• McMicken Thermostat Another Thermostat