Kinetic Art: The Shift Register, A Circuit for Sequential Switching of Lights

Leonurdo,Vol. 5, pp. 59-61. PergamonPress 1972. Printed in Great Britain KINETIC ART: THE SHIFT REGISTER, A CIRCUIT FOR SEQUENTIAL SWITCHING OF LIGHTS David Smith* During 1970, while a student at Sydney University in Australia and a member of the Optronic Kinetics Group there, I constructed my ‘Kinetic Kaleidoscope ’ (cf. Fig. 1) [l]. The on-off or flashing lights in the array making up the picture are operated by an electronic circuit called a shift register. I will describe this circuit before giving details of the construction of the picture and my reflectionson the application of modern technology to art. The shiftregistercircuit can be made easily by one who has some experience with digital switching electronics [2].Basically,it consistsof a circuit made up of any number of identical devices, called ‘JK’ flip-flops, connectedin seriesasshowninthe diagram in Fig. 2. A view of the circuit as it appears from the rear of the picture is shown in Fig. 3. The variable voltage output of each flip-flop controls a transistor switch that allows or disallowsthe current toflowthrough a 12V, 2Wlightbulb. Thetransistor conducts when the voltage output at its base is a predetermined value. The properties of an individual flip-flop are the following: It has two voltage outputs, indicated by Q and in Fig. 2, each of which can have either a high or a low voltage level. The two outputs are always complementary, that is, when Q is low then is high and vice versa. For a change in output to occur, a trigger or initiating pulse, generated by a clock circuit, must be applied. The type of change in output is also determined by the input voltage levels on terminals J and K of each flip-flop. Each of the terminals Q and are connected to the input terminals J and K of the adjacent flip-flop, as indicated in Fig. 2. If the input levels at J and K are changed and a trigger pulse is applied after each change, the following corresponding changes in output occur: When J is high and K is low, Q becomes or remains high; when J is low and K is high, Q becomes or remains low; when both J and K are high, Q remains unchanged after triggering and, finally, when both J and K are low, Q becomes the opposite of what it was before triggering. Fig. 1. ’Kinetic Kaleidoscope’, kinetic picture with sequentially switched lights, 250 Watts, max., 90 x 105 x 22 cm, 1970. The output Q of any flip-flopmay also be changed by applying an external voltage to it. For example, if Q is low and an external high voltage is applied to it by closing switch B, then Q will change to its high value and remain there even after the switch is opened. When the shift-register circuit consisting of a chain of flip-flops is first turned on, the output Q of each flip-flop is low and none of the bulbs will light up. If one momentarily introduces a positive external voltage at switch B to the Q output of the first flip-flop, it will change to this value and cause the first bulb to light up. Upon this occurrence, the inputs J and K of the second flip-flop receive the new voltage and, according to the properties of the circuit described above, the first trigger pulse will cause bulb No. 1 to extinguish and bulb No. 2 to light up. The second trigger pulse causes No. 2 to extinguish and No. 3 to light up and so on. Thus, information in the form of voltage level is passed along the chain, its presence made evident by the illumination of a bulb. The eyes see a light that * Electricalengineerand artist livingat 16A StationStreet, Pymble,N.S.W.2073,Australia. (Received26August 1971.) appears to move continuously from bulb to bulb. When the voltage information reaches the last bulb, 59 60 David Smith SWLTCH c Fig. 2. Diagram of shijit register sequentialswitching circuitfor ‘KineticKaleidoscope’. it is directed back to the first bulb by a feed-back line and the cycle repeats itself. By introducing the change in voltage level at...