modern railway level crossing lights

A magnet under the train operates reed switches positioned on the track. The trigger reed switch starts the sequence by switching on the amber light, a few seconds later the two red lights start to flash. When the train has passed the level crossing it operates the cancel reed switch which switches off the lights until the next train arrives.

There is a PCB pattern for this project, but if you don't have facilities to make PCBs you can build this project on stripboard instead.

Parts Required
Level crossing lights

* resistors: 680 ×3, 1k ×3, 33k, 47k, 82k, 270k
* capacitors: 0.1µF ×3, 10µF radial ×2
* red LED (3mm best) ×2
* amber* (or yellow) LED (3mm best)
* some amber LEDs are too orange to look correct, yellow may be better
* 555 timer IC ×3
* 8-pin DIL socket for IC ×3
* on/off switch
* battery clip
* reed switch ×2
* miniature magnet - each locomotive needs one
* printed circuit board (PCB)

block diagram of model level crossing lights

PCB component layout

The reed switches can be held in place between the rails with a small piece of blu tac.
Each locomotive will need a miniature magnet glued to its underside, test first with blu tac, then use superglue.

light sensitive alaram project

The circuit detects a sudden shadow falling on the light-sensor and sounds the bleeper when this happens. The circuit will not respond to gradual changes in brightness to avoid false alarms. The bleeper sounds for only a short time to prevent the battery running flat. Normal lighting can be used, but the circuit will work best if a beam of light is arranged to fall on the light-sensor. Breaking this beam will then cause the bleeper to sound. The light sensor is an LDR (light-dependant resistor), this has a low resistance in bright light and a high resistance in dim light.

* The light-sensitivity of the circuit can be adjusted by varying the 100k preset.
* The length of bleep can be varied from 0.5 to 10 seconds using the 1M preset.

Using the 7555 low-power timer ensures that the circuit draws very little current (about 0.5mA) except for the short times when the bleeper is sounding (this uses about 7mA). If the circuit is switched on continuously an alkaline PP3 9V battery should last about a month, but for longer life (about 6 months) you can use a pack of 6 AA alkaline batteries.