[better]: Ulp.txt

This approach allows the greenhouse owner to change operating parameters by editing ULP.txt on a laptop and moving the SD card—no firmware reflash required.

If you suspect a ULP:

void parseULP() File file = SD.open("ULP.txt"); while(file.available()) String line = file.readStringUntil('\n'); if(line.startsWith("#")) continue; int sep = line.indexOf('='); if(sep > 0) String key = line.substring(0, sep); String val = line.substring(sep+1); key.trim(); val.trim(); if(key == "target_temp_c") targetTemp = val.toFloat(); // ... other assignments ULP.txt

To configure ULP.txt , follow these steps: This approach allows the greenhouse owner to change

Some projects extend ULP.txt with simple conditionals: The bootloader reads it to set register values

In devices like environmental sensors, wearables, or industrial controllers, ULP.txt resides on a small SPI flash or EEPROM. The bootloader reads it to set register values. Because the file is plain text, field engineers can update parameters via a serial terminal without reflashing the entire firmware.