ABSTRACT RADIO REPEATER POWER SUPPLY MONITORING SYSTEM SCADA PT PLN (PERSERO) APD ACEH By NANDA NURMAULIDA 1404005010014 Radio repeater power supply monitor is a device based on ATMEGA-8 microcontroller. This device supervised power supply and battery condition in realtime. If problem occur, this device sending an information over Short Message Service (SMS) to admin. Power supply damage is overvoltage and undervoltage. If power supply damage occur, this device will shutdown the power source to repeater, so that will not damage repeater. If main source 220V absence, this device automatically transfer power source from power supply to battery. That will keep repeater operated. While battery voltage reach below 11 volt, this device will shutting down repeater power source, so battery not damage because overdischarge. Keyword : AVR, ATMEGA-8, repeater, SMS, power supply, ATS (automatic transfer switch)