A waterproof DS18B20 probe stuck deep in your compost pile feeds an Arduino Nano which logs to an SD card every 10 minutes.
DS18B20 needs a 4.7k pullup between data and VCC. Power the SD module from 3.3V via the Nano regulator (NOT 5V - the SD card is 3.3V).
| Component | Qty | Spec | Cost | Source |
|---|---|---|---|---|
| Arduino Nano | 1 | ATmega328P | $5 | — |
| DS18B20 waterproof probe | 1 | 1m cable | $3 | — |
| SD card module | 1 | SPI | $2 | — |
| 4.7k resistor | 1 | $0.05 | — |
01
Wire the DS18B20
Red->5V, Black->GND, Yellow->D2 with 4.7k pullup to 5V.
02
Wire the SD module
CS->D10, MOSI->D11, MISO->D12, SCK->D13.
03
Upload sketch
Sketch logs `<unix_millis>,<temp_c>` every 10 minutes. Watch the LED blink on each write.