Back logic display tutorial.

Ordedring info at the end of this page.

The back logic consist here of a printed cirquit board. ( PCB) The board is double sided and has already all the holes, these holes are metalized trought and trought , this makes them strong and easy to solder.The arangement has 4 rows of 27 LED's . When the LED's are soldered they fit exactly into the bezel made by another builder Damien ghost@lvdi.net

The whole work consists of soldering all 3mm LED's in place ,and adding 16 resistors .

Finally you have a PCB that fits exactly on the surround of the back logic display.

It is possible to fit the whole thing " as is" on the display surround.

The LED's are 16 series of 6/7 LED's strings. The strings are connected together in pairs this brings us to 8 command lines wich will control all the LED's .Each serie has a resistor connected in series wich can be adapted to have a equal light intensity on every string , this because the string consists of LED's of different colors and as different colors ,and certainly when in series ,sometimes need a few more volts than others..( If you have 5 reds and 2 greens in a string this need two volts more than 2 red' and 5 greens...) I did use all the same resistors and that works fine, but perhaps with ultra bright LED's or LED's that have a bit different caracteristics it may be possible that you need to slightly adjust the resistor values. I did buy my LED's from West Florida components they offer special packages for R2D2 cost only $ 5,95 ( $8,80 shipped to europe)

The LED strings with there series resistor all work on 24 volt, i used this voltage as in most cases this tension is available from the feet batteries.

To command the LED strings you can use different devices or timers , i use in this example the cheap K169 pic flasher. ( $17) Google for "K169 pic flasher" and you will find several places where it's sold.

The material and schematic

The schematic is really simple, just strings of LED's .

This is how the colors are placed, according to the designs i found in the builders group.Of course the wiring is different.

On the lower side the 8 square holes to connect the commands.

At the sides the holes to fit the series resistors.

LED placement .

All led are directed and placed on the PCB in the same way.The cathode ( shortest wire of the LED) is facing the 8 square holes of the board and the LED's are of course at the component side of the board ( the board is marqued component and solder side). If you have any doubts about the direction of the LED's connect the led at a 3 volt battery , when the LED light up the - wire of the led has to face the PCB side where the 8 square command holes are located.

Placement of the LED"s on the PCB (example: first row +one in the second row.)

Starting .

Use a good fine tipped soldering iron, and very fine solder.You need very little solder on each connection.Solder one row at the time and snip off the leg exces.

Solder the LED's row by row that way you have an easy acces.

The LED's all soldered on the PCB.

Equipped with the template from Damien. If you use the template , during soldering of each row place the template on the row new added LED's and then solder, this will keep the alignement 100% accurate.

I found out via messages of the builders group, and afther mounting mine, that Damien has different types of bezels!! Althought they are 4x27 the distance between the holes varies VERY slightly. Therefore sometimes it is better to start soldering the LED's starting from the middle of the PCB and working outwards, while aligning the LED's by mounting the bezel temporally every time you solder a new row of LED's . Do not cut the legs to short, use LED's legs that are slightly longer that way it is easy to bend the legs a little bit to realise a perfect alignement.

The resistors.

The resistors come at the side of the print , you find at each side of the print 8 single holes and 4 pair of connected holes. Those paired holes are the commons for the two connected rows, and each pair is connected to one of the commands. So if at the end all 16 resistors are in place you ends up with only the 8 commands and one common +24volt point.

The placement of the resistors is as follows .

All resistors are 3,3Kohm this gives a good brightness on all rows , the 14 LED rows and the 13 LED rows.

Finished with resistors ( all 3,3 Kohm) .

To check everything now , connect a 24 battery between the common + on the PCB ( a square hole located in the middle of the print at the opposit side of the 8 square command holes). and apply the 0 volt( ground) at each of the commands. Each row will lite up.

Fitted with the template of Damien, and connected to the PIC flasher with a piece of flatcable from an old computer hard-disk.

I did use the cheap K169 versatile pic flasher to command the logic. The flasher has 8 outputs each one is connected to a command of the PCB.

Final result.

Only a video clip can show it , so here we go: ....

Here mounted into the dome .................

Total cost = LED's 5,90

Resistors ............... 0,85

Pic flasher = ........ 17,00

Board = ................ 40,00

I only offer the board , no ready made display's ,but if you can solder there is no problem what so ever!

Price is 40 euro Paypal at leon.b1@scarlet.be

Shipping = 2 euro anywhere in the world, as i can put the pcb in a normal enveloppe IF you order more than one pcb, 1 euro extra as the letter will become heavier.

The board is no longer available.