synced using infrared phototransistors

Below is the circuit I`m working with; I plan on having the infrared phototransistor pairs inserted in 3 locations in the middle of the maze, including the end point. The width of the maze will be small enough for one finger to be able to slide in it, and as both fingers pass the phototransistors, they will cause a sound to be emitted from the spe
synced using infrared phototransistors - schematic

aker. This page presents information on infrared Across The Track` train detection circuits. The circuits are designed around the LM339 quad comparator chip and can use a wide assortment of matched infrared emitter / detector pairs. There is also a method that can be used for longer range across track detection that could be used for yard throats. A detector circuit of this type is in use at the London Model Railroad Group`s club layout and spans seven O  Scale tracks using one infrared LED and a lensed phototransistor. In the circuit bellow the LED will turn on when the infrared beam is broken. The value of the resistor R1 determines the sensitivity of the phototransistor Q1. In most cases a value of 1 Meg or 470K ohm with good results but every situation is different and some experimentation might be needed. Circuit Operation When a train breaks the infrared beam the phototransistor will conduct less current. The voltage at the MINUS input of the comparator will rise above the reference voltage at the PLUS as determined by R3 and R4. The output of the comparator to turn ON and the LED will be lit. Good alignment of the emitter and detector is important for good operation, especially if the gap is large. This can be done with a piece of string stretched between and in line with LED and phototransistor. A length of dowel or stiff wire could be used to set the alignment. Another method that can be used for longer distances...

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