K.I.T.T

Knight Rider led animation



Created by: J. de Waal, 2020-01-31


Knight Rider bicycle light

When cycling in the dark it is important to have proper lighting to be visible. A single red light bulb can be a bit boring. That’s why I came up with the idea of making a small animated rear light. The animation consists of 6 red leds, which light up from left to right and back, creating an effect similar to the scanner on KITT as seen in the Knight Rider series.

The animation

After some research, it seemed that using a decade counter was the best option for creating the animation. Together with some OR-gates is was possible to create the animation. The counter used is a 4017-CMOS IC. These come in a convenient dip-16 package. These come with the advantage that they have a wide input voltage range. However, the output current is limited. This is why transistors are used to control the leds. Using a clever voltage divider, the transistors can double as OR-gate, limiting the parts needed.

The design

While some parts of the design were well thought out, most of it was formed live at the Klushok. During building the connections on the output of the IC were shifted to make the part layout easier. This choice was determined by the placement of the pins of the IC. This only influences the starting point of the animation.

Power

The circuit gets its power from a 9v battery. This is connected using a cable that has a connector that fits the battery. Because the IC can handle a wide range of input voltages no regulator is needed.

Clock signal

For the animation to work a clock signal is needed. It is possible to use a 555-timer circuit. But for this version a transistor based astable mulivibrator was used. Using a variable resistor the frequency of the clock can be varied between 3 and 28 Hz. The counter divides the frequency by 10, so the period can be varied between about 0.3 and 3 seconds. This makes it possible to set the timing to match the scanner from the Knight Rider series.

The voltage divider

To control the transistors the gates are connected to one or two outputs of the counter using resistors. The resistors are calculated to form a Thevenin equivalent that can activate the transistor when one of the two connected outputs on the counter is high. Here it is helpful that only one of the connected outputs can be high at any time. By connecting the emitter of the transistor to ground and connecting the collector to the positive voltage via a led and an appropriate resistor, an OR-gate was formed. This also solved the problem of the maximum output current of the counter. For the leds that did not need an OR-gate, there is only one resistor going to the output from the counter. This provided the current to drive the leds on the far left and right of the bar.

Building

The complete circuit was made on a protoboard. The board has all the leds in a row to display the animation. To save on parts, board space and soldering work, there is only one resistor shared over the leds. This is no problem because at any time there will be exactly one led that lights up, resulting in a constant current drawn. After building, the project worked as soon as a proper IC was inserted in the socket. Some work was needed in order to tune the oscillator frequency range, resulting in some stacked resistors and an external potentiometer.

Conclusion

When the idea for this project came up, the intention was to make a rear light for a bicycle. However, mainly the leds used are not suited for this purpose. The light emitted is not bright enough and it is directional. This makes the light hard to see from an angle. However, because transistors are used to drive the leds, it is possible to use brighter leds if the resistor value is changed accordingly. The circuit behaves in an unintended way if the power source makes no proper connection. Therefore, a capacitor should be added parallel to the battery in future versions. Also a power switch should be nice to turn of the circuit without the disconnecting the battery. At last, some form of reverse voltage protection could be implemented to prevent damage from reversing the polarity on the battery.