Rancang Bangun Model Sistem Pemantauan Tinggi Muka Air Sungai Menggunakan Telemetri Radio

The early warning system of flood is used to prevent and minimize a damage to be happened. The primary element for the early warning system is water level of river, using distance measurement based on ultrasonic wave. The objective of this research is to make an instrument that functioned to measure water level of river and send the data to data center using radio frequency. This instrument is designed using the microcontroller as a trigger sensor and time of flight numerator of ultrasonic wave, result of the measurement is modulated using FSK then sent using the radio wave at frequency 88 108 MHz. Data which have been received then sent to computer in order to be presented and recorded. For 100 m from sensor, water level can be measured with one millimeter scale, with 0.61percent deviation for clear water. For dirty water, the deviation is 2.29 percent. Water level of river that modulated at modulator FSK for high logic is 5.98 percent, and for low logic is 6.22 percent. The stability of modulator frequency for all logics is good. Keywords: early warning system of floods, sensor ultrasonic, radio telemetry