Tiny, low power temperature sensor based on DS18B20.

The main scope of this project was to have dirt cheap, wireless, tiny and portable temperature sensor powered by batteries for at least 4+ months.

Requirements:

(Hardware)

• ESP8266 (ESP01) + Low power mod
• 4.7k resistor
• 2x1.5 AAA/AA batteries
• Battery holder
• Working MQTT Server
• Graphana (optional)

(Software)

• Temperature values will be sent to an MQTT broker
• Store the data into a database
• Plot nice graphs :)

Let's build it!

1. Deep sleep mod.There is a way to make ESP-01 work for months* using something called deep sleep mode. When in deep sleep, ESP8266 disables almost all of its functions and reboots after specified period of time. There is one catch: ESP-01 is capable to enter deep sleep, but unable to restart and resume operation. XPD_DCDC MCU pin in not connected to RESET pin. To fix it, you would have to solder thin wire between XPD_DCDC and RESET pin. There is a good article explaining in details how do to this. I also have removed the red power led from the ESP01 board what saved 10mA more.

2. Wiring see the image below:

3. Upload the sketch

Restults

Power consumption: Active: 133.2mA Idle: 18.6uA

Updates

After running on 2AA batteries for less then 4month (less then expected) I have decided to replace 2AA with one CR123 Lithium battery. This battery, in theory should last for about 2y.