Direction Pointer

Many times we find an arrow pointing direction of a shop, in movie halls giving you the indication of exit door or in malls to give you direction of staircase or wash room. But in night or in dim light it becomes quite difficult to find the way. So at such places you can install this direction pointer which will produce an eye catching appearance than any other ordinary direction pointer.

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Fig. 1: Prototype of Direction Pointer Circuit on Breadboard

This simple direction pointer circuit is made with the help of an IC CD7404 with few more commonly used components. CD7404 is the most commonly used Complementary Metal Oxide Semiconductor (CMOS) chip. It comes in a 14 pin Dual Inline Package (DIP). It has small notch on one side which identifies as pin 1. It consists of 6 independent NOT gate on a single chip. Each gate has 1 inputs and 1 output. Working voltage range of IC is from 5V to 16V. It can deliver approx.10mA at 12V but this can be reduced as power supply voltage reduces.

IC consist of 14 pin and pin 7 and 14 is connected to battery or DC power supply. Negative is connected to pin 7 and pin 14 is connected to power supply. As we know it has six gates we call it NI1, NI2, NI3, NI4 and so on. In first gate NI1 pin 1 is for inputs and pin 2 is for output. As you can see in the circuit below, its outputs goes low when input is high and its output becomes high when input is low, that’s why it is known as inverter IC.

Fig. 2: Pin Diagram of IC CD7404

In this circuit four sets of LED are arranged in the form of arrow and each set is light up one by one to give you indication. When power supply is provided, input pin of gate NI4 and NI1 are at low level as initially capacitor will behave like a short capacitor and inputs of both the gates are connected through a resistor R4. Because of this output pin 8 of NI4 becomes high and it will drive the transistor T1 into conduction and LED 1 and LED 2 connected to it start glowing.

At this time low at input pin 1 of NI1 make the output pin 2 high (therefore transistor T1 will not conduct) which is connected to input pin 3 of NI2 therefore after certain delay because of resistor R1 and capacitor C1 output pin 4 of NI3 becomes low and it will drive the transistor T2 and LED 3 and LED 4 connected to it start glowing.

Now again pin 4 is connected with pin 5 of NI3 so it will make the output pin 6 high and the transistor T3 connected to it start conducting and LED 5 and LED 6 will glow after some delay because of resistor R2 and capacitor C2. Now this high is again feed to pin 1 of NI1 and pin 9 of NI4( transistor T4 will not conduct) and at this time output pin 2 of NI1 become low and transistor T1 comes into conduction and LED 7, LED 8 and LED 9 will glow after some delay because of resistor R3 and capacitor C3. And this cycle is repeated until power supply is provided.

Arrange the LED’s in the form of arrow to point the direction. In order to slow down the speed of glowing LED’s increase the value of resistor R1, R2 and R3 and capacitor C1, C2 and C3.