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A dual (2 lead LED) can be simply driven with this circuit. As shown it was used on a 2 aspect signal with a separate marker light (for APB blocking)
For 3 aspect heads a transistor drive is suitable if there is a relay as the block detector output. This one described in Railroad Modeller July 2002 is simple and driven by switching the require LED circuit to ground. Red over-rides all other drives. The red also outputs a line to the previous signal which is used to interlock it to yellow. The Green input can be driven by the preceeding signal going red for active signalling or else it is tied to ground to display all the time.
A dual (2 lead LED) can be simply driven with this circuit. As shown it was used on a 2 aspect signal with a separate marker light (for APB blocking)
For 3 aspect heads a transistor drive is suitable if there is a relay as the block detector output. This one described in Railroad Modeller July 2002 is simple and driven by switching the require LED circuit to ground. Red over-rides all other drives. The red also outputs a line to the previous signal which is used to interlock it to yellow. The Green input can be driven by the preceeding signal going red for active signalling or else it is tied to ground to display all the time.
LINK TO IMAGE - sig-tdrive.gif
Circuit Schematic
