diff --git a/htu21d.h b/htu21d.h
new file mode 100644
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--- /dev/null
+++ b/htu21d.h
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+// Dario Lemus 01/oct/2026
+// HTU21D temperature and humidity sensor library
+// tested in a raspberry pi zero w
+
+#ifndef HTU21D_H
+#define HTU21D_H
+
+// commands and i2c address
+#define ADDR 0x40 //i2c address
+#define HUM 0xE5 // hold master humidity command
+#define TEMP 0xE3
+#define RESET 0xFE
+
+// prototype functions:
+int getTemp(int fd, double *temp);
+
+int getHum(int fd, double *hum);
+
+#endif // HTU21D_H