• (FYI : I am currently not posting the projects in chronological order, because I have so much stuff lying around that I did before I had the blog. So those things will show up from time to time.)

    The 4×4 LED Display was my first project with a two-layer circuitboard layout. The alignment was not 100% optimal, but sufficent. I wanted to make the board as small as possible, so the parts had to be stacked at some places. The square LED’s were painted black on the sides to keep the pixels sharp.

    4x4 LED Matrix Circuit Board (Top)

    4x4 LED Matrix Circuit Board (Top)

    The rows and columns are both controlled by a 4094 Shift&Store-register. The upper four bits control the coloumns and the lower four the rows. So for each frame 4 bytes have to be shifted in. That is done via a QBasic programm that toggles pins on the serialport. Instead it would also be possible to just send the bytes over a serialconnection, but I was to lazy to write code for that.
    To generate the patterns, one can put them together binary by hand. But I choose the easy way again and wrote a Delphi-Program to generate patternfiles, which then would be send to the display by a QBasic programm. (I test all my circuits on old DOS-PCs).

    Here is a video of the display in action. The sequence is preprogrammed…so no actual tetris yet..

    Layout and circuit are here. QBasic sourcecode is too ugly to show. How to shift data into a shiftregister should be easy for everyone who can read the datasheet.

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  • Christmas Lights reused

    Top view

    When clearing out the basement a found an old chain of lights for christmas decoration. Many bulbs were burned out but a litte box at the end looked worth opening, as the lights could blink in different patterns. Inside the biox was an IC and four transistors for driving the lamps.

    Christmas Lights reused

    Bottom view

    I plugged it in and measured the signals at the pins of the IC and discovered, that the chip was clocked by the mains frequency but needed no other signals except a button for switching the pattern.

    I decided to replace the lamps by leds and place everything on a small circuitboard.
    At every channel of the IC there are four blue leds. All sixteen leds are placed in a circle around the other parts.
    The clock is generated by a good old NE555 timer.

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