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 ^.^)

 

Moved from General Electronics Chat to Homework Help.

 

What is the desired flash pattern for "police lights"?

Are the flash patterns for both circuits the same?

How do the two circuits create their respective flash pattern?

 

Moved from General Electronics Chat to Homework Help.

how do i do that?

 

What is the desired flash pattern for "police lights"?

Are the flash patterns for both circuits the same?

How do the two circuits create their respective flash pattern?

he didn`t specify any particular flash pattern...i guess that is for me to decide
i have no ideea if they are same...
i don`t even know how to answer the last question...

can you maby please explain how those questions are relevant and how dose the circuit differ when the pattern differs? it would help me alot

 

Hello,

You likely got the schematics from the following sites:
http://www.electro-tech-online.com/threads/police-flash-lights.103089/
http://www.555-timer-circuits.com/police-lights.html

For the one with the resistors, what happens in the base of the transistor (look at the extra diodes 1N4148's).
Why are no outputs of the 4017 skipped?
For the one with the diodes, look how the signal would look like at the base of the transistors.
Why are outputs of the 4017 skipped?

Bertus

PS MrChips did move the tread for you.

 

Hello,

You likely got the schematics from the following sites:
http://www.electro-tech-online.com/threads/police-flash-lights.103089/
http://www.555-timer-circuits.com/police-lights.html

For the one with the resistors, what happens in the base of the transistor (look at the extra diodes 1N4148's).
For the one with the diodes, look how the signal would look like at the base of the transistors.

Bertus

PS MrChips did move the tread for you.

haha you are right about the 2nd schematics (the one with the diodes) as for the first one, that was given to my by my teacher... in the complete picture of the first schematics there is a link to www.talkingelectronics.com, but its the same schematics as the one on the electro-tech

how do i "look " how the signal would look like at the base of the transistor...i`m guessing i need to simulate the circuit ? i`m thinking about doing it with orcad? that is the software we are using at my university...

 

Hello,

Only 1 pin of the 4017 will be high, all others will be low.
With the resistor schematic, a voltage divider will be created.
And what will the 2 diodes 1N4148 do in that schematic?

What will happen in the diodes schematic?

Bertus

 

i like the fact that you answer with tips and questions, this is great. as this is the first time i try to understand things not just to memorize things, it will take me some time to answer your question because i don`t even know how to abord the questions , i need to review some of my documentation and try to figure out how all that circuit works..! i will be back with answers

 

i like the fact that you answer with tips and questions, this is great.

We need to introduce you to a member known as, Yakima. I am sure he will convince you of the errors in this perception.

 

The first circuit uses the 555 to turn off the leds, at each clock pulse, your circuit uses every other output of the 4017 to put the leds on then off.

 

We need to introduce you to a member known as, Yakima. I am sure he will convince you of the errors in this perception.

as i can`t think of any for myself i really would like him to explain his opinion on this aproach to me you really should introduce me to him

 

Hello,

Here is the internal schematic and timing diagram of the 4017:

This might give you an idea how the 4017 works.
I also attached the complete datasheet for you.

Bertus

 

Hello,

Only 1 pin of the 4017 will be high, all others will be low.
With the resistor schematic, a voltage divider will be created.
And what will the 2 diodes 1N4148 do in that schematic?

What will happen in the diodes schematic?

Bertus

uh uh i think i got it, i have major problems reading this schematics , i never know where to start "reading / interpreting " a schematics, but i think i partialy got this one...so here goes nothing, i`ll try to answer . so after i study the " counting action of the 4017 decade counter" i can see WHY "Only 1 pin of the 4017 will be high, all others will be low."...depending on where that 1high is ,1 of the 2 diodes will conduct current trough it...if 1 conducts current the other one is blocked , disableing the tranzistor that is wired to it, while the one conducting will create a flow of current from it`s transistor emitter terminal trough it`s base. wich will then enable the emitter - collector current to flow, thus lighting up the leds conected to it...is that corect? if not ask me more question so i can deduce why it`s not corect

 

Hello,

I have made the question for the resistor circuit in a drawing, to visualize it:

Bertus

 

The 4017 moves the outputs one at a time from 0 to 9, only one output is high as it clocks the output moves along to number 9, your using every other output, so it pulses the transistor on and off via the diodes.

 

Hello,

I have made the question for the resistor circuit in a drawing, to visualize it:

left picture : the first diode will have low on kathode and high on anode right (because ?1 will be high?) that means it will conduct, while the other one will have low on both terminals (because ?2 is low), so it won`t conduct.......i think..?

 

ok so i feel like when i have LOW the diodes will conduct SO the lights will be off...because the current will go trough the diodes, not the tranzistors...and if i have HIGH they will be blocked...and then magic happens and the lights are on....i wish i had a more engineering reasoning for this..this is just gut feeling

 

no when the outputs are low the diodes are off, transistor is off, led is off, ...

 

Hello,

When the input of the diode is low, it will conduct and the transistor can not be switched on.
When the input of the diode is high, it is in reverse connected, and no current can flow through it, the current can go to the transistor, so the led will be on.

Bertus