4017 & 555 Police LED Lights Project (noob question)

[10101010]

hello, i am assigned to create a physical project starting from the schematics on the left side. my teacher told me that the schematic is incomplete, so the first step is to corect it and then use pads and then send the gerber files to a company to create it. i started reserching it and every schematics i found on the internet about this project had a major diffrence...in my schematics the outputs of the IC 4017 is conecte to 6 resistors...on a number of other similar schematics they are connected to 6 diodes...this is my first project and it is the first time i have to use my electronics knowledge to do something from a tp z and aparently i don`t have much of it

...can some one please talk to me about the diffrences on those schematics...can any one shed some light for me on this subject? i will be forever gratefull

thank you in advance

(sorry for my bad english, i hope you understand what i am talking about ^.^)

 

[Gryd3]

Tomaeto Tomahto.
The resistors allow current to flow both directions... so the 4017 will form a voltage divider. If the values are chosen properly, there should be enough current to trigger the transistor further down the line responsible for the lights.
The diodes only allow current flow in one direction (toward the transistor) and would be the easier one to design/troubleshoot, and more of the output from the 4017 would be directly sent to the transistor.

 

[BobK]

Agree. They are just wasting power compared to the diode solution. Perhaps this is one of the "mistakes" your prof wanted you to find.

Bob

 

[10101010]

nice. thank you all for the feedback it really helped. i think i figured it out. now i`m thinking to be a little arogant and add a speaker with the sirens of a police car, any toughts on that? i presume i need to make some major changes to the project but it`ll be worth it cuz i`ll stand out from the crowd .

 

[10101010]

so this seems an easy enough schematics...i just need to try and interpret it. if i do this more i`ll get good at it lol this is fun

 

[Colin Mitchell]

The siren circuit is a very bad design. It does not have any current limiting.

"They are just wasting power compared to the diode solution. " This is incorrect.

 

[Gryd3]

The siren circuit is a very bad design. It does not have any current limiting.

"They are just wasting power compared to the diode solution. " This is incorrect.

Lets slow you down a little Colin.
The circled parts of both diagrams refer to section responsible for ORing the output pins of the 4017 together.
Both diagrams have a current limiting resistor before the transistor, and for each series sets of LEDs. So they do indeed have current limiting.

Can you please be more specific on why the resistor layout is not wasting power?
Only thing I can think of is if the voltage drop across the resistors are higher than the 0.6-0.7V forward drop of the diodes... but then again, this allow allows current to flow between 4017 pins from high into the 3 remaining low pins.

 

[Colin Mitchell]

Here is the simplest circuit:

http://www.talkingelectronics.com/projects/50 - 555 Circuits/images/PoliceLights-2a.gif

 

[Colin Mitchell]

"Both diagrams have a current limiting resistor before the transistor, and for each series sets of LEDs. So they do indeed have current limiting."
I said the Siren Circuit.

 

[Colin Mitchell]

"Can you please be more specific on why the resistor layout is not wasting power?"
The resistors perform two functions. They limit the current and form a "gating" function.

 

[10101010]

hmmm well i changed the siren circuit....i have finished my led circuit and i understood how it works...i was thinking to connect another 555 timer as a clock generator witch i will connect to a BDX53 , 93 transistor witch then will be conected to my speaker...the IN of my 2nd 555 will be the OUT of my first 555....i also tought i would use a pontetiometer betwen my first 555`s 7 pin and 8 pin, thus i can control the freq of my output witch is = to controling my led`s freq of blinking....i don`t understand why i need to capacitors next to my leds...what is the role of that? here is the shcematics for my design...the part of my siren circuit is drown separatly from the main circuit, on the bottom left of the paper, i`ve explained how i want it connected so can you please tell me what you think about that idea?