VvTP atom simulatorThe VvTP is the Student Society for Applied Physics. The logo of this society is an atom.
As a promotional stunt, the yearbook committy wanted to build a huge, moving atom simulator. Since no one of the committy knew enough of electronics, they asked me if I could help them building it. So I started to make a design.
The schematic consist globaly of 5 parts: a power supply to convert the incomming high voltage to 5 volts (7805), an oscillator (40106), a binary counter (4020), a 4-to-16 decoded (4514) and a few output stages (ULN2804 + BD140).
The power supply is very basic and build around a 7805 voltage regulator. Also a fuse and a reverse polarity protection is added. If the polarity is reversed accidently, diode D1 will short-circuit the fuse and thereby protecting the eletronics.
The oscillator is build around a 40106 Schmitt-trigger. A potmeter is added, to make the speed variable. This signal is then devided by the 4020 binary counter. Every output devides the frequency of it's previous output by 2. The 4 uppermost bits are sent to the 4514 4-to-16 decoded which makes 1 of its outputs high based in the binary input. The 5th bit is sent to a few inverters to select led columns 1-16 or 17-32. The last few bits are used to blink the big letters on the billboard.
Since the ULN2804 drivers can only sink current, 2 PNP transistors (BD140) are used to source current to the LEDs. On the last ULN2804, a few outputs are used in parallel to increase the maximum current.
Fortunatly, this schematic performs very well and is still working after 2 years of continious work.