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This was designed to operate a turnout for the approaching train. The photocells were set between the rails about 2 engine lengths back from the point in the approach rails. The points would then be set to allow the train to proceed through. A momentary contact double throw switch was in circuit to allow manual setting of the points.
When the light to the top pcel is cut off by the train it allows the 555 timer threshold voltage to rise and time out. This puts pin 3 low and drops the relay. Changing the points setting.
If the lower pcel is covered the first transistor high output switches the second transistor on which applies a negative trigger to the timer. This sets pin 3 high and picks the relay. The manual switch puts a low or high pulse onto the timer pins 2 & 6 to cause the same sequence.
This was designed to operate a turnout for the approaching train. The photocells were set between the rails about 2 engine lengths back from the point in the approach rails. The points would then be set to allow the train to proceed through. A momentary contact double throw switch was in circuit to allow manual setting of the points.
When the light to the top pcel is cut off by the train it allows the 555 timer threshold voltage to rise and time out. This puts pin 3 low and drops the relay. Changing the points setting.
If the lower pcel is covered the first transistor high output switches the second transistor on which applies a negative trigger to the timer. This sets pin 3 high and picks the relay. The manual switch puts a low or high pulse onto the timer pins 2 & 6 to cause the same sequence.
LINK TO IMAGE - auto-1.gif
Circuit Schematic
