555 police lights (noob question)

Hello enginners,

I don`t know if this is a good place to ask my question since it is a probably stupid question to you, but i am new to this and i need some help..hope some1 will acord 5 minutes to reply..here it goes

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 ^.^)

The new diodes are fine, the part that you need to add is the two diodes from pin 3 of the NE555. They should be wired directly between pin 3 and the base pin of each transistor. Without them the lights will still operate but you will not get the rapid flashing effect, only the lights operating in sequence.

Brian.

The circuits are different but I think they both work and perform the same function. I think one runs at twice the speed of the other one.
Both circuits use diodes as logic gates but the diodes have different quantities and are in different positions on the two circuits.

Build both circuits to see.

Audioguru said:

The circuits are different but I think they both work and perform the same function. I think one runs at twice the speed of the other one.
Both circuits use diodes as logic gates but the diodes have different quantities and are in different positions on the two circuits.

Build both circuits to see.

Click to expand...

would it help if i try to use orcad to simulate both circuits? will it show the diffrence ? , also, my teacher say that i need to slightly modify the schematics because it is incomplete...

Try simulating and see.
The use of diodes in the new schematic is more efficient than the resistors used in the old one. Note that only one of the 4017 outputs is high at a time so the diodes are there to turn the tansistors on when those outputs with diodes are active but isolate the outputs from back-driving each other. Functionally, it makes no difference whether you use one diode per output and a single bias resistor or use lots of resistors and a single diode.

The missing part is the two diodes (1N4148 on the old schematic) to pull the base voltage of both transistors low enough that they are prevented from conducting at 'clock' speed (the output of the NE555).

Brian.

Resistors work OK at 12V where 3 R's load each other so you end up with 1/3 of 12V=4V before next stage load

1st circuit uses 2 diodes to turn off both LEDs, 2nd does not.
2nd using Diodes give more base current for bigger LEDs

2nd uses pattern 0 off 2 off 4 5 off 7 off 9 0 off...repeating


Both circuits waste way too much voltage on LED current limit resistors, or else you can add more LED's in series with each easily (3V/Blue,White) (2V Red) then recalc series R aor possibly run off 3.7V Lithium with small R (50) or 5V logic voltage.

Police LEDS use many 1W LEDs and maybe pulse at 3W, which means you ought to use MOSFET switches instead of transistors with logic level drive since transistors need about 10% drive current into base.

The diodes in the first circuit with all the resistors turn off the LEDs each time the 555 output goes low. Then each group of LEDs can blink 3 times. It will work the same without the diodes if it uses every second 4017 output like in the other circuit.

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 .

The circuit you showed is for LEDs to blink. A siren circuit will be completely separate.

Audioguru said:

The circuit you showed is for LEDs to blink. A siren circuit will be completely separate.

Click to expand...

was thinking of something like : if leds blink, speaker goes on. something easy..probably gonna need some memory . i have time, this project needs to end in the summer ^^

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1011010 said:

was thinking of something like : if leds blink, speaker goes on. something easy..probably gonna need some memory . i have time, this project needs to end in the summer ^^

Click to expand...

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

Police flashing lights are fairly standard throughout the World but the sirens are different in almost every country. I think you are in Romania but I haven't worked there for a few years and never got chased by the Police while there so I'm not sure what they sound like. Your best strategy is simply to make a siren oscillator and run it from the same supply as the LEDs, in other words it isn't connected to the flasher at all, just turns on at the same time.


Brian.

In some places it is a class A misdemeanor. to impersonate an emergency vehicle but Romania , who knows.

But if you are just wanting to play at home a phone ringtone connected to a 100W Amp into a Horn Speaker under the hood ought to do the job. Then pulse about 4 Amps into a some 50W LEDs with a MOSFET ought to get U a buzz or kicked out of the house.

@betwixt : curious how`d you know i`m from Romania ? well i can`t say i got chased by police either , cuz i never run from them, even tough i know some police stations from Timisoara as i had my share of night life (drinking ,partying, got out of control and stuff). It dosen`t really matter how they sound since this is a project for my school, i would like it to sound like an atomic alarm..you know that long siren that goes off in movies when the bad guyz lunch the bomb? that`s a cool sound .

@SunnySkyguy i didnt get the first paragraf of youir last comment

I`m not playing at home this is a project i have to do for my university, i have until the semester ends . the initial project was only the police lights but i find it fairly simple and i wanna add the siren part to it as i have alot of time on my hands, well i should study for the physics exam but meh, this is to interesting. i feel like i`m learning alot from this project...i think projects are the way to go when you wanna learn electronics...not sure about it but it is defently alot of fun ^^

Forum moderators can check the IP address used when posting the message and I could see yours was from a .ro domain.

It was Timisoara where I worked ! - its a small World. You can probably guess where, the big factory on route 6 next to the CocaCola building.

The best way to make the siren is as I described, you need two oscillators, one to make the audio tone and a much slower one to make it shift in frequency. I could describe the schematic but there must be hundreds of designs on the Internet. Just feed the siren circuit from the same switch that powers the flasher unit. There is no point in trying to make one circuit do the flash and siren, the way they work is completely different.

Brian.

no way? Flextronics? i worked there for 10 mounths, last year, i was a tehnician debug there in module 1 ^^ first job to get some xp under my belt ^^ .

i will defently try it with the oscilators, dosen`t sound very hard i will put up some circuits once its done

Same place, but before you were there.
I was installing and customizing test equipment for "bed of nails" in-circuit testing of telecoms PCBs.

Brian.

bed of nails..that is Takaya , in the first 2 months of my time there as debug i was responsible to find out why the PCB don`t pass the takaya and ICT (in circuit test) tests. then i sustained an exam and i got promoted to functional debug and i was responsible for every machine in the module (the module was new and they have no good ppl working as debugs so they trained us ,lucky us ^^). but after that they say they cannot promote me higher, so here i am back to school trying to get a degre

Not Takaya, it was a system from 'Mindready Solutions' but it was several years before you worked there. Most of the ICT was provided by SPEA at the time I was there, I worked with their engineer, he sorted out the component level testing and my machines did the functional testing. It was for Telecoms products, probably at the end of their life as the work was moved to Timisoara as production in Wales started scaling down.

Brian.

i don`t think they are still working on Telecoms products now...we were working on alcatel lucent`s LTE and MRO , MCO, things like that...but i got the job 2-3 months after they got the contract for those projects...and no one knew why they were failing in the tests...it was in interesting job...not boring at all, as we were facing new problems every day...in other modules where every fail was known and the debug had only to check a textbook to see what PN to change so the board passes, we had to do investigations on boards, i`ve learned how to mesure , they even let me use the specter analyzer a few times , even tough under observation ....i really miss that job

ok i`m back. i went to my supervising teacher (we have to meet once a week so we can talk about the progres in the project) and i was disapointed to see that he didin`t care i understand HOW the circuit works...aparently all he wants is for it to work so he has at least 1 working project. Well , i don`t care what he cares, i will give my best to understand what i`m doing here. so i have the first part figured out...i understand how the 555 works, i understand how the 4017 works, and i have a sugestion about how to add a speaker to my project...i was thinking of using another 555 as a signal generator, the 2nd 555`s IN will be the first 555`s OUT... and the 2nd 555`s OUT will be connected to a BDX53 , 93 transistor witch will work as an amplif, and that will be conected to the speaker...here is the updated photo of my new schematic....the 2nd part of my circuit is drown in the bottom right corner. on this pic is all i know about my circuit...i also tought that i can add a pontetiometer betwen my first 555`s 7 and 8 pin because i understand that controling the rezistence there will get me to controll the output freq of my 555 and that is = to controling the freq of my led blinks....do you have any opinions on this thus far? my next move will be to drow the logic diagram with PADS, when i find the library of the compoents i need (btw if you know a good place i can download lib`s feel free to share )