Main components

Part number

Source

Cost (US$)

Microcontroller/cellular board

Feather 32u4 FONA

Adafruit Industries

45

Cellular antenna

Sticker-type GSM

Adafruit Industries

3

Rechargeable battery

3.7 V LiPoly, 2500 mAh

Adafruit Industries

15

Terminal block

Spring terminals

Adafruit Industries

3

Low-power timer

TPL5110

Adafruit Industries

5

Weatherproof enclosure

NBF-32002

Mouser Electronics

9

Miscellaneous (protoboard, headers, resistors, connector)

5

Total

85

Soil-moisture sensors (4)

Watermark 200SS

Irrometer Company

120

SIM card, cellular data plan

1 MB/month, 1 year

Embedded Works

30