Random Lights


Random lights for illumination of the model railways

This circuit performs, in an almost random form, on and off lights and accessories for the model railways. There are seven random outputs and the eighth to use, for example, as street lights to distinguish between day and night phase, having more or fewer lights on at one phase or another. It is based on the circuit Men at work and in this random flasher.

In the schematics you can see the parts that conform the circuit:

- An oscillator for the speed of the sequence

- A 7-segment decoder to provide the randomness

- An output stage to connect the lighting and accessories

the pseudo-random sequence obtained at the outputs is:

The part of the voltage regulator is mounted around a 78L05 as it only fed CMOS circuits, the consumption is small.

The oscillator consists of the 4060, it has its frequency set by R3 and C4, with the values shown there is a change every 85 seconds, so a day (repetition of outputs) takes about 45 minutes. Changing the value of C4 the time can be adapted to the day duration of your railway model.

The 4543 is a 7-segment decoder that converts the binary output from 4060 to something more random, besides having an entry that reverses the outputs are achieved more with less activated outputs states with which we can have two phases (day and night) be a more enlightened than the other

Each of the outputs of the 4543 active the ULN2803 to connect lamps or LED (house lights, etc. ..). If you mount LED, put the corresponding resistor for it. Also you can place a relay to the output if the power to control is more than 500mA or if you want to invert their operation.

Here you can see the prototype mounted:

Download the design of printed circuit board here in PDF format.