3D LED Pyramid

The author 'just wanted to do a bit of microcontroller programming'. However, the project rapidly grew into this impressive and visually attractive pyramid. The circuit consists essentially of a specially-sawn printed circuit board,  23 LEDs and a microcontroller. Despite the fact that the microcontroller  is a rather modest Atmel ATtiny2313, the author nevertheless has found room in the 2 KB flash memory for 16 different light sequences.

The 23 LEDs are divided into three groups. The lower and middle sections consist of eight LEDs, while the upper section  has just seven. The microcontroller has only 20 pins, and so it is not feasible to provide a direct individual drive for each LED. The multiplexing approach adopted uses just eleven output port pins. Buffer transistors are used to increase the  current drive capability of each output.

The software was written in assembler and can, as usual, be downloaded from the Elektor web pages accompanying this  article [1]  as either source code or as a hex file. The printed circuit board layout files are also available from the same  place, as well as a link allowing purchase of ready-made boards and pre-programmed microcontrollers.

Populating the printed circuit board is straightforward: there are some surface-mount components to be soldered,  but space is not tight. For best results,  it is best to choose LEDs with the widest possible viewing angle so that the pyramid  looks its best even when seen from the side. The author used type LO 1296 orange LEDs from Osram, which have a viewing angle of 160 '. A six- way connector is provided to allow in system programming  (l5P) of the microcontroller. The  configuration fuses are set to enable use of the internal4  MHz  clock source, which is divided down to 0.5 MHz by an  internal divider.  lf the fuses are not correctly programmed the light sequences will run too quickly, too slowly, or even not at all!

When everything is working, take an 11 cm length and  a 5.5 cm  length of 1.5 mmz solid copperwire and solder one end  of the shorter piece to the middle of the longer piece to make a 'T' shape. Pullthe  printed  circuit board spiral apart  so  that the T-shaped wire assembly fits underneath, and then solder it to the two pads as shown in the photograph. Fine-bore brass tubing can also be used instead of solid copperwire.

As well as the ISP connector a USB interface is provided, whose job is solely to provide a 5 V supply. An external 5 V mains adaptor would do the job equally well. Two jumpers affect the behaviour of the light pyramid: JP1 deter-mines  whether the sixteen sequences follow one another in strict order or at random;  and JP2 determines whether the light  patterns are displayed orwhether all LEDs will be continuously lit. S1 is a reset button, which will come in handy if you  wish to experiment with modifying the software.

Author : Lothar Goede - Copyright : Elektor