Creating LED Chaser Using 555 Timer and 4017 Decade Counters

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In summary, the individual is attempting to create a LED chaser using a 555 timer chip and 2 x 4017 decade counter chips. They are unsure about the correct way to connect the two chips and have provided a schematic for reference. Another individual suggests using 20 switching diodes to isolate the outputs and achieve the desired effect. However, it is noted that connecting outputs together in this manner is not recommended for digital chips. It is also mentioned that a series resistor is needed to limit current and that the Knight Rider circuit, which uses series diodes for special effects, may be a better option. The individual is unsure of the original intent but it is assumed that they are trying to have 20 lights come on in sequence,
  • #1
unknown_2
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hey, I've been looking at ways to create a LED chaser using a 555 timer chip and 2 x 4017 decade counter chips(more than 10 LEDs). mind you I've only been working with these chips for an hour. so here's the dilemma, I'm not quite sure if I'm right on connecting the 2 chips. what i did was connect the carry output pin of the first chip to the clock pin of the second chip. then i connected one of the last output pins of the second chip to both reset pins of the decade counters. i have provided a schematic below. is this correct or am i missing something?

Schematic: http://i20.photobucket.com/albums/b219/twiztedazn/SCHEMATIC1_PAGE1.jpg"

thanks,
 
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  • #2
it's not a good idea to connect the output of these chips like that, however, you can isolate them with 20 switching diodes (10 for each chip). A diode will conduct current in one direction, so if one pin on, current will be blocked by the diode in the other pin, and vice versa. That way the current will guided only to the LEDs.

You can employ the same trick using one chip, but with less LEDs

555-KnightRiderAnim.gif
 
  • #3
Your circuit should never have outputs connected together like that. This applies for almost any digital chip. Never connect outputs together.

With two 4017s you can turn on 20 LEDs but two at a time (One LED must be on for each 4017). The outputs just go to the LEDs and then through a common resistor to ground.
You do need a series resistor to limit the current, but since they are only coming on two at a time, it can be a common resistor.
Normally, you would have a resistor for each LED.

You do not need series diodes (in series with the LEDs) . That Knight Rider circuit had them because they were combining outputs to get special effects with the lights going backwards and forwards.
 
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  • #4
vk6kro said:
You do not need series diodes (in series with the LEDs) . That Knight Rider circuit had them because they were combining outputs to get special effects with the lights going backwards and forwards.

I think that's what he is trying to do.
 
  • #5
Yes, I'm not sure.

It seemed like if he had two 4017s he wanted to have 20 lights coming on in sequence.

However, in the simple circuit, it was necessary to have one light of each 4017 on at a time and this could be achieved with one 4017 anyway.

The Knight Rider circuit is better, anyway.
 

1. What is a 555 timer and how does it work?

The 555 timer is an integrated circuit that is commonly used in electronic circuits as a timer, oscillator, and flip flop. It works by using a combination of resistors, capacitors, and transistors to generate precise and stable pulses of electricity.

2. What are decade counters and how do they work?

A decade counter is a type of digital counter that counts in multiples of ten. It works by using a series of flip flops to store and display the count in binary form, with each flip flop representing one bit of the binary number.

3. How does the LED chaser circuit function?

The LED chaser circuit uses a combination of the 555 timer and decade counters to create a sequence of flashing LEDs. The 555 timer generates pulses that are fed into the decade counters, which then count in binary and activate the LEDs in a sequential pattern.

4. What components are needed to build the LED chaser circuit?

To build the LED chaser circuit, you will need a 555 timer, two 4017 decade counters, resistors, capacitors, LEDs, and a power source. You will also need a breadboard, jumper wires, and a soldering iron if you choose to solder the components together.

5. Can the LED chaser circuit be modified or expanded?

Yes, the LED chaser circuit can be modified or expanded in various ways. For example, you can change the flashing pattern by adjusting the values of the resistors and capacitors, or you can add more LEDs by connecting additional decade counters in series. You can also incorporate other components, such as transistors or switches, to create more complex effects.

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