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Display
Every display character consists of a matrix of 5 x 7 =35 light bulbs. In a piece of three-ply wood which has been painted white at front, holes have been drilled for the small lamps. At the rear comes the wiring which has been soldered to the lamps. The distance between the lamps amounts 1.67 cm. So there are 3 lamps on 5 cm.
With this measure the size of a display character is 10 x 6.7 cm. The size of a display with two display characters becomes about 23 x 16 cm. and of three display characters 32.5 x 16 cm.
Around every light bulb there has been glued a small paper cylinder with diluted glue to care that the light stays near the lamps. The dimension of the cylinder is 1.5 cm diameter and some mm. high. In the image there has some been drawn.
The displays with 2 or 3 characters should be mounted not to far behind the front plate of the total display so that the display keeps readable at very small angels.
At left one can see the shape of the figures, variations are possible. One could imagine that all these figures are on top of each other in the total display matrix. For every lamp a diode is needed. All added, one needs 150 diodes per display character. For 8 characters this amounts 8x150=1200 diodes. These are switching diodes of 100 mA. Try to get the cheapest diodes in dump shops or markets. They may be cheaper in big amounts.
For the support of the diode matrix one can use circuit board with metalized holes at 0.1 inch. distance. The total number of holes 10x35=350. Of these only 150 are provided with a diode. The 35 wires for the lamps are soldered over the diodes. For this one can use very thin un-insulated copper wire, for example one thin wire from a twin wire 220 V. cord. Perpendicular 10 wires from the relais are soldered at the bottom. Total there are 8 matrices needed.
At best every diode matrix can be mounted as close as possible to the character display, so that the 35 wires are as short as possible.
Schematic diagram of the diode matrix
On the diode matrix one may save room for a spare character. In that case there are not 10 but 11 wires at the bottom, so 10 for figures 1-9 and a character. As mentioned earlier, the BCD coding has 16 possibilities from which 10 are uses for the 10 figures. One of those extra possibilities may be used to display an extra character as an eleventh figure. If this bit combination is present (1010), a circuit controls a relais which disconnects the supply of the relais box and put supply to every eleventh wire of the displays. In my case the words: "HBV DE BUN" are displayed. So every diode matrix generates one character of the sentence.
