Model Train Diesel and Horn Circuit

The main power supply to the system must be a regulated 12 volts DC with a minimum input from the train control AC or DC power supply of 13.5 VAC connected to pos 3 and 4 of the rectifier bridge . The ground bus of the regulated 12 volts supply must be connected to the system ground , The independent speed reference voltage is taken directly from the train speed control module or can be taken by connecting directly from the tracks to positions 5 and 6 of the rectifier bridge .The output of this bridge will always be a positive speed voltage signal whichever direction the train is going.
Model Train Diesel and Horn Circuit - schematic

The op-amp used is a FET input type ( TL071) for minimum offset voltage without having to use a zero offset voltage circuit . The offset voltage for the 741 was found to be much too high at 2.3v while the TL071 average offset of 1.15 volts was ideal to ma

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