Sequentially shifting control circuit for extendible light strings

A sequentially shifting control circuit for extendible light strings comprising a main controller serially coupled with a plurality of bidirectional-shifting control units and a backward signal generating circuit, a single signal line and two power lines coupling said main controller, said bidirectional-shifting control units, and said backward signal generating circuit;

• synchronous signals for said control circuit having a level between 18 volts and 5 volts, forward data signals and backward data signals being synchronously interposed in a low level between zero and 5 volts and a high level between 18 volts and 30 volts, respectively, backward control signals being interposed in the synchronous signal and having a duty cycle greater than said synchronous signal, such that said signal line transmits said synchronous signal, said forward data signal, said backward data signal, and said backward control signal simultaneously;
• wherein said bidirectional-shifting control unit comprises two independent shift circuits, each of which comprises a shift register, said two registers having a plurality of output terminals, a corresponding terminal from each register forming a pair, each pair being connected to an OR gate which is further connected to a light, thereby constituting a light string, said two shift registers having data input terminals thereof and driving output terminals thereof being inverted to connect to two external terminals to function forward and backward respectively, said synchronous control circuit receiving said synchronous signal from one of said external terminals and connecting to said two shift registers at a clock terminal thereof, and through a transistor circuit to regenerate synchronous signals to couple to the other external terminal and transmit to the next shifting control unit.