Low cost low power room sensor with atmega328p and 433mhz transmission

Following my first build of an external garden sensor, here is a simplified version with temperature, humidity and battery voltage measurement for a baby bedroom

[EDIT] feedback about the expected battery duration here

The requirements are:

• cheap
• long battery life, the atmega328p run at 8mhz with minimal components and functions
• under 8€
• wireless (433Mhz) with good range (2 walls to cross and 10 meters)

Here is the final view attached to a lion for decoration:

And a report from OpenHab displaying the sensor data:

If you want more details about energy power consumption the first article on this subject is more detailled.

Now let's see how to build this.

Bill of material

The sensors is based on atmega328p(3€), 

• a 433 Mhz transmitter (1,5€) ,
• a DHT22 temperature and humidity sensor (4€),
• a 433 mhz antenna (0,18€)
• DIP socket adaptor for the ATmega (1€)
• an electronic prototype printed circuit board (0,5€)

At total we are around 8€

Principle

Every hour the sensor send the data to a 433Mhz gateway so as to be stored in OpenHAB, the data sent are:

• air temperature
• air humidity
• voltage of the power supply

The library used to send the data is RCSwitch.

The program to load to atmega328p on the sensor is here Low power sensor_inside

Steps to follow

The steps to follow are the same as the garden sensor, just remove the hygrometer sensor and you are done.