Design of a programmable logic controller auto power reset circuit for an FM transmitter

Abstract

The mono-stereo controller using an audio mute clock has been used at the International Broadcasting Bureau (IBB) FM 106.6 MHz transmitter in Ulaan Baatar, Mongolia since 2010. The major problem of the FM broadcast station was from a frozen programmable logic controller, PLC, that must be manually reset and the report by the VOA listeners. A PLC auto power reset circuit was proposed and built as a mono-stereo controller to monitor the operation of the PLC. The circuit was also used to restart the PLC whenever it became frozen. A cloud router and Transmission Control Protocol/Internet Protocol (TCP/IP) to a Recommended Standard Number 232 (RS-232) converter were used to synchronize the time parameter of the PLC. From the results, this circuit improved transmitter availability and quality of the 24 hours/day broadcast program without affecting the listeners. The reliability of the cloud router is acceptable with low delay of data transfer via the internet connection between Thailand and Mongolia. The cloud router, leased by IBB from a provider that offers Internet services at speeds of up to 1000 Mb/s via a remote terminal, is used for scheduled programming and correct time synchronization of the PLC. The proposed system is very stable and there has been no incidence of a frozen PLC when connected to the Internet or when it was disconnected. Hence, the designed PLC auto power reset circuit can be used for relief of this frozen PLC problem.