Design of remote temperature monitoring system tool using VHF waves based on VFC LM331

Abstract

A remote temperature monitoring system has been designed and manufactured using VHF waves based on VFC LM331. This remote temperature monitoring system uses the IC LM35 temperature sensor. The technique used for sending data uses radio waves on VHF lines with an OOK (On-Off Keying) modulation system. So that the analogue voltage signal from the sensor can be modulated and transmitted by the transmitter, the voltage must be converted to frequency using a VFC LM331. From the results of measuring the accuracy of the design tool, it was found that the design tool worked well at a temperature of 0 oC up to 99% compared to a reference device. The range of the system that has been designed is much influenced by the frequency of the transmitter used, the more users on that frequency, the shorter the range. The farthest distance that can be reached is around 120 meters at a frequency of 80 MHz while at a frequency of 89 – 106.3 MHz it can only reach around 48 meters.