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KnightRider LED Scanner This circuit simulates the row of scanned lights used on the car in the KnightRider TV series. The PC board has a row of 16 LEDs which are scanned back and forth continuously at a rate which can be set by an on-board trimpot. While it is many years since the “KnightRider” series was featured on TV, it still creates interest. In particular, the row of scanning lights in the bonnet of the car has been the inspiration for a number of circuits. We published one in the November 1988 issue of Silicon Chip. That circuit had two sets of 10 LEDs interposed into two rows. This new circuit has one row of 16 LEDs and is more realistic, scanning in one direction and then the other. The circuit presented here is based on a design submitted by Andersson Nguyen, of Bankstown, NSW. At his suggestion, we’ve simply taken his circuit and produced a PC board for 80  Silicon Chip it. The 16 LEDs are mounted along one edge and only two wires go to the board: +9V (or up to +12V) and 0V. How it works The core of this circuit is a 4029 presettable up/down counter. It is made to count up, then down, then up and so on. It counts from 0-15 and back again in BCD (binary coded decimal). The four outputs (A, B, C & D) are decoded to give 16 individual outputs by a 4514 (IC4) which drives the LEDs directly. Fig.1 shows the relevant circuit details. IC1, a 555 timer, provides the clock pulses for the 4029 presettable up/ down counter, IC2. It oscillates at By RICK WALTERS several Hertz, as determined by the 2.2µF capacitor and the setting of the 100kΩ trimpot VR1. Its output at pin 3 drives the clock input of IC2 at pin 15. IC2 can be set to count to any value from 0-15 by means of four jam (preset) inputs – pins 3, 4, 12 & 13. However, in this circuit, we want the full count so the jam inputs are not used; instead, they are tied low. Therefore, it counts from 0 to 15 then back to 0 again and its four BCD (binary coded decimal) outputs are connected to IC4, a 4514 1-of-16 decoder which drives the 16 high-intensity LEDs. Thus, as the 4029 (IC4) counts from 0-15, the output pins (S0-S15) of this IC will each go high in turn, lighting Fig.1: the KnightRider circuit is simple and, just as important, simple to build. It is designed to be mounted in a vehicle, hence the regulated power supply. This can be omitted for battery or fixed supply use. the LEDs which are connected to these pins. Outputs S0 (pin 11) and S15 (pin 15) of IC4 are connected to the set and reset (pins 7 & 4) inputs of IC3, a 4027 dual JK flipflop, only one of which is used. Pins 5 & 6 of this 4027 are held high and pin 3 is held low, allowing it to act as an RS flipflop. The Q output (pin 1) of the 4027 is fed to the up/ down input, pin 10 of IC2, so that every time the first or last LEDs are lit they cause a change in the counting direction. Thus, the up/down counter will now count up from 0-15, then down to 0 again. Since only one LED is on at any time, a single 1kΩ resistor can be used for current limiting. The value of this resistor can be altered to suit the LEDs that you use but do not reduce it much below 1kΩ, as the outputs at S0 and S15 will be loaded so much that the RS flipflop will not toggle. Diode D1 is included for reverse polarity protection. The 10Ω resistor and 15V zener diode ZD1 are only needed if you intend to operate the scanner in a motor car. If not, omit ZD1 and fit a link for the 10Ω resistor. Putting it together We have designed a PC board measuring 95 x 88mm which is coded 08105961. Before inserting any components, check the board carefully against the PC pattern in Fig.3. Look for any undrilled holes, shorts between tracks or breaks in the copper pattern. There should not be any but if there are, it is better to find and fix them at this stage, than to tear your hair out later when the board does not work. Start by inserting and soldering the 19 links, then the resistors and diodes. As the easiest way to assemble a board is to insert components in order of increasing height, the next groups will be the ICs, LEDs and trimpot, followed by the capacitors. Before installing the LEDs, it is a good idea to test at least one of them for polarity, since some LEDs now available are being supplied with the May 1996  81 PARTS LIST 1 PC board, code 08105961, 95 x 88mm Semiconductors 1 555 timer (IC1) 1 4029 up/down counter (IC2) 1 4027 JK flipflop (IC3) 1 4514 1-of-16 decoder (IC4) 1 1N4004 diode (D1) 1 15V 1W zener diode (ZD1) (see text) 16 5mm high intensity LEDs (LED1-LED16) Capacitors 1 10µF 25VW electrolytic 1 2.2µF 25VW electrolytic 1 0.1µF MKT polyester Resistors (0.25W, 1%) 1 10kΩ 1 1.2kΩ 1 1kΩ 1 10Ω (see text) 1 100kΩ horizontal mounting trimpot (VR1) Fig.2 (below): use the printed circuit board overlay (below) in conjunction with the pattern (Fig.3, right) to make the construction simple. Don't forget to check the PC tracks for any damage before inserting the components. 82  Silicon Chip longer lead as the cathode instead of the anode. Using a 9-12V battery, connect one end of a 1kΩ resistor to the positive terminal and the other end to the anode of the LED. The cathode of the LED should be connected to the battery negative. You can also use a DC power supply for this test. If the LED doesn’t light, reverse its leads. If it now lights, the lead going to the resistor is the anode. If it still doesn’t light, it is a dud. Looking at each LED from the front of the PC board (LED edge), the cathode is the left lead while the anode is the right lead. When you have finished installing and soldering all the components, check your work carefully against the circuit and wiring diagrams. This done, apply power and the LEDs should immediately start scanning from one side to the other. Remember that regardless of the speed of scanning, only one LED is on at any one time. Use the trimpot to set the scanning speed. And if you want the circuit to drive 12V light globes . . . The circuit at right shows how to interface the KnightRider with high power (up to 35W) 12V bulbs. Only one circuit is shown, but you would need to build up 16 of these to have the full effect of the KnightRider. Note that the interface circuit can either replace the LEDs (LEDs 1-16 on the circuit) or, if you wish, can be connected in parallel with each LED so that the LED display operates in sympathy with the light bulbs. There is no provision made on the PC board for the interfaces. It may be possible to solder the Darlington transistors direct to the lamps or lamp sockets. The DC supply for the lamps should be taken via a suitable fuse from the battery side of D1, not from the reguSC lated supply.