ATtiny84 Low power LoRa node

In this post I will show you the development of a Low Power LoRa node with a ATtiny84. A lot of thanks to the guys on The Things Network forum. I took their code for ATtiny85 and modified it to use it for a ATtiny84. I used this processor because I was familiar with it and has more IO pins.

Main modules/electronics used:

  • ATtiny84A microprocessor
  • BME280 sensor
  • RFM95W LoRa module

Technical specifications:

  • 4.8 microAmpere in sleep mode (3.3V)
  • 100mA @51 ms sending data SPF7
  • About 2.2-3.6 V power supply (Lithium Battery)
  • Measurement of Supply voltage, Temperature and Humidity in current version of the software.

Picture of the latest version:

Final version of the node

I used 675 Zinc-Air Batteries to create a real small LoRa node. Here a picture to compare the size to a 9V battery:

The PCB size is 45 x 20 mm. Maximum height is about 18 mm without housing.

The schematic:

The code can be found at https://gitlab.com/iot-lab-org/ATtiny84_low_power_LoRa_node.git

** NEW ** 2018-05-15: OOP code at https://gitlab.com/iot-lab-org/ATtiny84_low_power_LoRa_node_OOP.git

The schematic and PCB design can be found at https://easyeda.com/Leo/ATtiny84_LoRa_Environment_Node-d542dfbcc50d456c80869380bc979266

The total cost (typically Dutch):

Device Shop/webshop Price
ATtiny84 eoo-bv.nl  €       2,90
RFM95W aliexpress.com  €       4,60
BME280 (inclusief header pins-6 voudig) aliexpress.com  €       2,99
Printplaat LJK1801 EasyEDA  €       1,98
Batterijen (2x) 675 Zink Air Kijkshop  €       0,67
Batterij-veren Hackerstore.nl  €       1,10
IC-voet 14 pens eoo-bv.nl  €       0,16
C 100nF, raster 5 mm MKT eoo-bv.nl  €       0,15
C 470uF, 10V, 8,2x12mm axiaal eoo-bv.nl  €       0,10
Header-6pin female martoparts.nl  €       0,25
Header-2pin male martoparts.nl  €       0,03
Dupont-2pin female krimp martoparts.nl  €       0,10
3D print matriaal behuizing  €       0,23
Totaal  €     15,25

 

Current measurements:

Remember to remove the resistor on the BME280 to reduce current in sleep mode. Here (not) shown in second place from the top at the (original) 5 SMD parts.

The calculations I did to get the lifetime. Please correct me if I am wrong:

Information:

  • 4.8 uA in sleep
  • 100 mA @ 51 ms pulse every 5 minutes.

Power used in a year:

rest: 4.8 * 10E-6  A * 24hours * 365.25 days = 0.04104 Ah = 41.04 mAh per Year

sending: 100 *E-3 A * 288 measurements a day * 365.25 days * 51 * 10E-3 seconds / 3600 seconds in an hour = 0.149022 Ah = 149.022 mAh per Year.

Total 190 mAh per Year.

Useable time:

675 Battery (Zinc-Air):  640 mA => 3.37 Year

LS14250 Battery (Lithium): 1200mA => 6.3 Year

LS14500 Battery (Lithium): 2450mA => 12.9 Year

(This is incredible!, I do not believe it)

 

Testing:

I am now testing a few nodes: outside, in the freezer (-20 degrees Celsius) and room temperature with different batteries.

Inside (box) and outside closure:

I designed and printed this closure myself (3D print). You only have to add 2x M4 x 60mm bolts and 2x M4 nuts. I made the design public available: http://a360.co/2FBE9M9. You have to print the mid-section a few (8) times. I learned that it is called Stevenson screen. My design has the looks but not the scientific usability :smile:

 

 

 

2 thoughts on “ATtiny84 Low power LoRa node

  1. Hello,

    Thanks for the complements, great to hear that you’re gonna use my design. Have fun with it!

    About the 470uF capacitor:
    Because of the 3.3 V working voltage a 6,3 Volt Capacitor would be enough. I bought a 10 V capacitor because a 6,3 V was not available or the size was not appropriate for my (physical) design.
    You may choose yourself what size or voltage you want to use. The capacity is also arbitrary, I did not make any calculation. Ik know when the RFM95W is sending data It wil draw 100mA in 50uSeconds.
    I guessed that will be heavy load for the battery, so I decided to add this capacitor to catch this pulse a bit, and to prevent the voltage to drop to much near the end of the lifetime of the battery.

    The 100nF capacitor you mentioned is fine. This 100nF capacitor is a (default) interference suppression capacitor for high frequencies.

    Leo.

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