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This is a simpler, but still effective DC Block detector than the Twin-T. The circuit was supplied by Roger Smith in a signalling article in the NZ Model Railway Journal of June 2003. It uses the voltage drop generated across two rectifier diodes of 1.2 volts to activate an optical coupler. This needs to be an AC type or a two 4N35 types connected with opposite voltage inputs. H11AA1 has a transistor output, a TLP620 darlington transistor type could be used for greater sensitivity. The output is isolated from CAB power and lights a LED and provides a low logic signal.
As with both current detectors there is a loss of track voltage. All blocks on the layout must have a double diode in the supply line or a slow train will speed up in an uncompensated block.
This is a simpler, but still effective DC Block detector than the Twin-T. The circuit was supplied by Roger Smith in a signalling article in the NZ Model Railway Journal of June 2003. It uses the voltage drop generated across two rectifier diodes of 1.2 volts to activate an optical coupler. This needs to be an AC type or a two 4N35 types connected with opposite voltage inputs. H11AA1 has a transistor output, a TLP620 darlington transistor type could be used for greater sensitivity. The output is isolated from CAB power and lights a LED and provides a low logic signal.
As with both current detectors there is a loss of track voltage. All blocks on the layout must have a double diode in the supply line or a slow train will speed up in an uncompensated block.
LINK TO IMAGE - det-diode.gif
Circuit Schematic
