LED scanning arrow sign

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Sometimes a few components are enough to make simple yet useful circuits that can be assembled even by beginners. With just two ICs and a handful of LEDs, you'll be able to make this LED scanning arrow sign. 

LED scanning arrow sign animated image

This eye-catching, decorative light arrow could well find its place in a display window to draw the customer's attention to an item or group of items. It could also mark a direction or an entry or exit point that we would like to indicate to an audience, etc. 

LED scanning arrow sign electronic circuit
LED scanning arrow sign electronic circuit

As shown in the circuit diagram, there are only two integrated circuits, a 555 and a 4017 plus four NPN transistors used to power groups of LEDs in series. NE555 IC1 is connected as an astable multivibrator. By adjusting trimmer R1 so that its resistance is fully short-circuited, a frequency of about 5 Hz is produced at pin 3 of IC1 and, in this condition, the sweep speed of the LEDs is maximum. If we set R1 for maximum resistance, the frequency of the astable multivibrator becomes about 1 Hz and the sweep speed is then minimal. 

The CD4017BC is a 5-stage divide-by-10 Johnson counter with 10 decoded outputs and a carry out bit. This counter is advanced on every positive edge of the clock signal provided by the 555. 

As shown in the wiring diagram, output pins 3, 2, 4, and 7, which correspond to the least significant (lower) outputs of the counter, are connected to the bases of transistors T4, T3, T2, and T1. When an output is at a logical high state, it turns on the corresponding transistor and the corresponding group on LEDs. At the first four clock pulses, pins 3, 2, 4 and 7 advance sequentially.  On the fifth clock pulse, pin 10 goes to logic 1 and resets the counter, since it is connected to the “reset" pin 15. A new counting cycle starts after each reset. 

The circuit can be powered from any 12V DC power supply unit or from any battery. The current consumption is about 30mA. 

How to assemble the LED arrow sign electronic board
How to assemble the LED arrow sign electronic board

The brightness of the LEDs depends on the values of resistors R8, R9, R10 and R11. R11 has a slightly smaller value than the rest since it regulates the current flowing through a group of 5 LEDs while for the other resistors, each one regulate the current in a group of four LEDs. If you wish to have higher or lower brightness on the LEDs, you may decrease or increase the values of these resistors accordingly.  

To assemble the circuit, you can build the printed circuit board, based on the instructions provided below. The circuit board can easily be placed into a small stylish box in which you will have to drill some holes to fit the LEDs.


Printed circuit board artwork for the LED scanning arrow sign.


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