Low Power Thermostat

Here are the code and schematics of a IoT enabled, low power Thermostat, based on a Moteino board. It has a build-in 868MHz radio to transmit information to a base station and, therefore, push data the cloud.

The thermostat itself works just as a switch to the heater control line; no AC supply is needed.

Key features:

• Current temperature set point and ON/OFF modes are configurable through an Android app. :-)
• Low power (idle current of ~25uA). No AC supply needed. Can run for months with 3xAAA, LiPo, etc.
• OLED screen as a HID.
• 3 modes of operation:
  • Turn the heater ON for a period of time.
  • After a period of time, turn the heater ON for another period of time.
  • Temperature set point with a configurable 1ºC hysteresis.
• IoT enabled through another Arduino based device connected to the Internet.

Links:

• https://thingspeak.com/channels/400806/

TODO

• Connect the Thermostat directly to the Internet, keeping a low power profile.
• Add an RTC in order to program the Thermostat based on week days, day time, etc.

Changelog

v1.1

• Switched from DHT22 temperature sensor to HTU21D.
• Aprox 100ms of sleep task time.

Program:   22370 bytes (68.3% Full)
(.text + .data + .bootloader)
Data:        929 bytes (45.4% Full)
(.data + .bss + .noinit)

v1.0

• First stable version.
• Android app connection is working.
• Issue. 250ms delay after temperature sampling to avoid incoherent readings.

Program:   23292 bytes (71.1% Full)
(.text + .data + .bootloader)
Data:        896 bytes (43.8% Full)
(.data + .bss + .noinit)