Garry is a standard PC, that was fixed inside the house without any type of case. The PC prepares the signals from the software so that they can be used by the shift-registers on Paula. The 450 MHz processor is underclocked and is only running at 400 Mhz to keep power-dissipation low.

Controlling 144 lamps isn't easy, especialy when those lamps need to be logic '0' or '1' at all times. This means that we would need 144 outputs from the PC, but since the centronics-port can only offer a fraction of those outputs we had to find a different solution. The original Blinkenlights control PC used three expansion cards with 48 outputs each. This would have been an elegant but also expensive way of solving the problem, so we decided to use the 18 8bit shift-registers like BlinkenLEDs.

In this example all memorys contain logic zero (0V) [1]. A bit-combination is applied to the input and then a short impulse to the clock-input. After that has happend, the first bit of the combination has been shifted into the first cell [2] and therefore the first parallel output ~> the first lamp is on. If the register is „clocked“ again the second bit moves into the first cell and the first one is moved to the second cell [3]. With the next clock the third bit is moved into the first cell and the ones in the cell are moved on [4]. After the eighth clock all bits are in the cells, and the lamps, corresponding to the bit-combination, are on [5]. In this way the first bit at the input is moved into the first cell an the bits already in the register are moved forward by one cell.In our case the clock-signal is so fast that the single steps can't be registered by the human eye. Just about as soon as the bit-combination is applied, all the bits would have „fallen“ out of the serial output.

This means, that it is possible to control 8 lamps with one output of the centronics-port. But to control 144 lamps the port would need to have 18 outputs, so we had to use a little trick. With help of the serial outputs of the shift-registers two or more registers can be cascaded [6]. With this method 16 or more lamps can be controlled and therefore we only need 9 outputs from the centronics-port. The house has 18 columns with each 8 rows, therefore one output controls 2 columns.

The 18 shift-registers on Paula, cascaded to 9 sets of 2. This can easily be seen from the bottom of the PCB.

The ICs 1&2, 3&4, and so on are cascaded. This means that pin 10 of the first IC is connected to pin 02 of the second IC etc. The supply-voltage for Paula is connected to K1, here 12V. IC19 is a fixed 5V voltage-regulator (78L05), that is connected to pin 16 of all shift-registers. C1 and C2 are 100nF bipolar capacitors, C3 is a 10µF electrolytic capacitor. These three capacitors stabilise and smooth the supply-voltage of the shift-registers. An overview of all connections that come from Garry, can be found above in "Modular connector K2''. Because Paula has quite a few traces, the PCB had to be double-sided, but nevertheless a few wire connections had to be made.

Since 36V incandescent lamps where used for the house it was not possible to connect the lamps directly to the shift-registers. To obtain the higher voltage and current needed, the signals from Paula have to be amplified.

As can be seen on the pictures, Agnus is also a double-sided PCB. The 144 N-channel enhancement-mode MOS-FETs are assembled to a low-side-amplification-circuit (left picture). Every lamp has it's own FET. The lamps are directly connected to 36V, and when the FET is switched the other side of the lamp is pulled down to ground ~> then the lamp is on.

Here you can see Paula at the front with ribbon cable to Garry, and Agnus with the 144 wires that go directly to the lamps. Nothing should be canged round here.

Denise is more or less the case for Paula, Agnus and Garry and consists of medium density fiber boards , plastic-glas and a lot of screws. We bought 7 boards of MDF-wood with 16mm thickness and the following dimensions:

2x 75,0 x 115,0 - front, back wall
2x 20,0 x 113,4 - side walls
1x 75,0 x 28,2 - base plate
1x 75,0 x 20,0 - ceiling plate
1x 71,8 x 113,4 - insertion [lamp-holder]

All boards are still the same size, except for the lampholder, which was shortened at the top and bottom to improve air circulation.

Building the house

The first step was to screw the boards to a box, so that we could see, if everything would fit properly, and to drill the holes for the screws. This was the first time that we noticed, how large our construction would be. Then the box was dismantled again and the positions of the windows where sketched on to the front. Then two holes had to be drilled for each windows so that we could use the jigsaw to „cut“ out the windows. Larger windows where sawn into the back and the top to be able to see the inside of Denise. A large round hole was sawn into the top for the case fan and another into the back for the aluminium plate with the switches and socket. A few leftovers where enough to make four „feet“. When everything was sawn, we started varnishing. Every single unit has to be varnished two or three times, until the colour properly covered. At the end we put clear varnish on the outsides. We still had to drill 144 holes into the lamp-holder, on which we sticked aluminium foil for reflection. The amount of time we spend for all that can be estimated at about a week (five to six hours per day) in a not heated garage in the middle of November. At this point we want to thank Emsa, a company which produces very good thermal coffee pots. After the work in the garage we could get inside, where it was nice and warm, to do less rough work. First we wired up the reflector, that means the threads of all lamps were connected with each other and then the lamps were screwed into the reflector.

Denise is not only the case for Paula, Agnus and Garry, but also the power-source. An aluminium panel with power socket, two power switches and two micro-switches was fixed to the back of Denise. The first power switch connects the two transformers to the mains. The first transformer [24V 160VA] supplys the lamps through a bridge-rectifier [80C35A], a 10.000µF electrolytic capacitor and a amperemeter at around 35VDC. The second transformer is a PCB-mount type [15V 25VA] ,connected to the adjustable power-supply [0V – 15V], supplies Paula, case-fan and the fan for cooling the 160VA transformer. A blue fluorescent lamp was also fixed inside Denise for better illumination, and also draws its current from the adjustable supply. The second power-switch connects Garry to the mains, and the micro-switches are to reset and switch on Garry.

After the cut up Persplex panes were installed behind the window holes, only Paula, Agnus and Garry had to find their place in the case. Then the lamp-holder was built in. In addition a "raster" was put on screws in the lamp-holder. It is used to divide the light from every single lamp, otherwise also the neighbour windows would be shining. To suppress this effect we further put seal tape (actually used to seal doors and windows) between raster and lamp-holder to make the windows as lightproof as possible. Thanks to Jan, Kathes brother, for this great and cheap idea. While the "indoor work" the front wall was painted by Cindy 'Slide' Krause. She painted the original communist marquetries in oil on it, now it looks like the real house of the teacher. The original frieze was made 1964 by Walter Womacka.

After the front has dried Denise could at last be put together completely. This happened, after nearly two months of building and constructing, on December 20 of the year 2002.

The complete Littlelights documentation is available in the docu section for download.