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Presepino: the nativity scene with Arduino

Presepino: the nativity scene with Arduino

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A light system, capable of simulating the alternation of night and day, that will make your nativity scene – be it a small or a big one – even more realistic. Our circuit is capable of piloting four light loads, corresponding to the daylight, to the brilliance of the stars, to the household hearths, and to the guiding star. It allows the control of LEDs and of a NeoPixel strip.

 

presepino featured

As with every year – with Christmas time approaching – we think about a themed project that might be able to make it even more original and warm. We decided to opt for a nativity scene control box, but we deemed right to make it in a modern and topical key; and with “topical” we mean the usage of hardware that has been experienced and appreciated, that is what thousands of experimenters could find in Arduino. This Presepino was born, that is to say, a light and sound control box for nativity scenes, whose circuit is based on the ATmega 328 microcontroller (therefore, that’s Arduino UNO’s hardware) and created so to directly command some LEDs, with all the relevant advantages: the first among all of them is the fact that it operates at a low voltage, and therefore it may be placed in the vicinity of children, without any danger for their health. Moreover, with LED strips being greatly available nowadays, it turns out to be very easy to create an automated nativity scene.

In addition to the lights, our Presepino enables the audio management, thanks to an innovative MP3 player module, mounted on the board, and capable of reproducing (even if in mono sound) all the tracks contained in a SD-Card.

 

The project

But let’s go in order and see – as a first thing – all the available functions, that differentiate our control box from those used for the simple control of two lights: dawn and sunset. With Presepino it is possible to obtain a control going beyond the one needed in small or big nativity scenes found in the houses, and one that is suitable for the nativity scenes prepared for the churches, for the parish youth clubs, for the community centres, and more in general for the places of worship. For this reason we created a circuit that is certainly a powerful one, and capable of driving four light loads, having LEDs operating at 12 volts and absorbing an individual power of 6 amperes; this is also the maximum current that the board may manage, and it can be powered by copiously tinning the tracks going from the power terminal box to the MOSFETs, and from the latter ones to the corresponding output terminal boxes. With “individual current” we mean that each channel may commute 6 amperes, but given the way the printed circuit board has been built, it is not possible to constantly absorb 6 amperes from all the outputs at the same time. These values, considering that the circuit was born for the purpose of piloting LED strips or – anyway – LED compositions, are more than adequate ones, and for a home nativity scene they are more than abundant.

The outputs for the terminal box are six, but the firmware we supply contemplates the management of the first four, so to implement the simulation of the daylight, of the starlight, of the hearths for (Bethlehem’s) hut/cave and for the shepherds’ houses, and finally of the guiding star’s lighting. The lights are progressively turned on and off, and follow a cycle that simulates the duration of the whole day.

To these basic outputs you may add the other two, by acting on the sketch for the ATmega 328 microcontroller: to them you may assign the control of various accessories in the nativity scene, such as a paddle wheel, the movement of animated characters or animals, and so on.

As regards the basic outputs, we divided the complete sequence in four phases, obviously named day, sunset, night and dawn. The duration of each phase may be independently adjusted; as for day and night, the duration is set between about 3 and 10 minutes, while the two transitions have a duration between about 20 and 100 seconds. Obviously the latter ones are the most evocative ones: during the sunset the day luminosity (SOLE output) gradually decreases, while the stars start to light up (STELLE output); at a certain point, before the cycle reaches its conclusion, the hearths in the houses and in the hut will light up (FUOCO output). By the way, our circuit is capable of simulating the flickering flames of the wood burning, by piloting the FUOCO output, by means of an appropriate sequence of pulses. When all the stars in the sky are completely lighted up, even the guiding star will appear (lighted by the COMETA output). Obviously, and except for some small details, during the dawn all the other lights will gradually turn off, while the “daylight” will reach the maximum luminosity.

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