LED 5 blinks and then a continuous light.

[SimonFrisendal]

Hello. I have been assigned a task of designing a brake light with the following specifications:
1. The circuit shall start when given voltage (Obviously!)
2. It must be operational within 10-16V.
3. It must blink 5 times, and thereafter light continously.
4. The Blinking frequenzy must be approximately 5 Hz or similar frequencies appealing to the eye.
5. As the system is designed to replace current brake lights the only signal coming from outside the circuit is the 12V from the car.

I tried sending a 5 Hz test signal into a CD4017B decade counter. I thought i could then take every second output into an or gate made up of diodes a transistor and resistors. I thought this would give the five blinks and that connecting the last output leg to the clock inhibitor would then make a continous signal after the five blinks. The circuit would be resettable by coupling the voltage off. The final circuit would then be made up of an NE555 delievering the 5 Hz.

But the problem is that i have hooked up the decade counter as i mentioned on a test bench, but i am only getting a high low shift on the legs of the decade counter and not on the rest of the diodes that only show a low signal. I thought this would work. What am i doing wrong and could i possibly add some pulse width modulation to make the circuit more efficient?

I'm sorry for this long post but i don't have anywhere else to go to. So thanks in advance.

Simon.

 

[DerStrom8]

Hi Simon. Welcome to ETO!

The post length is fine

5 hz is still quite fast--connected directly to this signal, an LED would blink 5 times in a second. Even taking every second output from the 4017 would give you 2.5 hz, which is still kind of fast to call a "blink pleasing to the eye". For that, I would suggest, maybe, 0.5 hz.

Could you post a schematic of your circuit? It's possible it is just a simple mistake in the wiring.

Regards,
Der Strom

 

[Reloadron]

I would as DerStorm suggest slow the clock down to about .5 Hz. You should be able to use the 4017 with every other output configured as a Count To N and Halt by placing pin 13 (clock enable) on N. Also, yes posting a circuit would be cool.

@ DerStorm nice holiday touch with Tesla.

Ron

 

[DerStrom8]

@ DerStorm nice holiday touch with Tesla.

Why, thank you, Ron You're the first person who has said anything about it

I got the idea from the mods over at AAC--they do something like that every year. I decided I'd follow suit

Regards

 

[SimonFrisendal]

**broken link removed**

The 5 Hz is reasonable as this is supposed to alert the driver behind the braking car. So the blinks need to "wake" him/her up and 5 Hz probably will! I haven't designed the final schematics yet so you will have to do with the schematic i drew in paint above. Thanks for the feedback and indeed a nice touch with Tesla

 

[DerStrom8]

The 5 Hz is reasonable as this is supposed to alert the driver behind the braking car. So the blinks need to "wake" him/her up and 5 Hz probably will! I haven't designed the final schematics yet so you will have to do with the schematic i drew in paint above. Thanks for the feedback and indeed a nice touch with Tesla

5 Hertz is not reasonable. That is what I was saying. At 5hz, chances are you won't even be able to tell it's flashing at all. It will just look like a steady light. 0.5 hertz means it will complete one cycle (on and off) in two seconds, connected directly to the LED. That is much more reasonable, but I would think that, maybe, 2 hz would be more what you're looking for. That would flash twice a second, which should be able to "wake up" the driver behind you.

However, I should mention that you could get in a lot of trouble by modifying the brake lights on a car. There are laws about that sort of thing, and depending on where you are it could be illegal. I imagine it could also be very distracting, and in a worst-case scenario could cause the driver behind you to get in an accident. I really wouldn't recommend modifying actual brake lights--it could be very dangerous, even if not illegal.

Regards,
Der Strom

 

[SimonFrisendal]

This is just a project for fun given to us by our teacher. It won't have any other application than flashing. The reason why we are doing this is to get experienced with different IC's

 

[DerStrom8]

This is just a project for fun given to us by our teacher. It won't have any other application than flashing. The reason why we are doing this is to get experienced with different IC's

Ok, just as long as you don't plan to use it in a real-life application ;-)

 

[SimonFrisendal]

I never will. That would almost equal a suicide attempt. Anyway. Do you see any reason as to why my circuit shouldn't work? I had it set up on a test bench and applied a clock signal i then tested for logical low and high with the test bench and the outputs on the 4017 do vary but after the diodes everything is just logical low. Thanks.

 

[DerStrom8]

Your diagram is slightly difficult to read, as it has some parts that are not drawn in standard form. It is difficult to tell which wires are connected and which aren't, but overall it looks ok. Next time, try drawing your circuit in a program such as . Also, try to learn some of the standard conventions for circuit design, as they will help you a lot in the long run

Regards

 

[SimonFrisendal]

I think that the resistors are causing problems. The boxes are resistors and i know that in the USA resistors look like: **broken link removed** . No wire interception and every where a wire meets a wire, a connection is occuring. I usually use PADS logic, but this was done in a hurry as you asked for a schematic

Oh and there is a transistor in the bottom left.

 

[DerStrom8]

I think that the resistors are causing problems. The boxes are resistors and i know that in the USA resistors look like: **broken link removed** . No wire interception and every where a wire meets a wire, a connection is occuring. I usually use PADS logic, but this was done in a hurry as you asked for a schematic

Oh and there is a transistor in the bottom left.

I know just about every schematic version of every individual component--I have been working with them myself, probably even longer than you have . I have used both the American style and European style resistor symbols before, depending on who the circuit was going to. My problem was the orientation of some of them, and the connections between wires. For example, common convention puts the ground symbols ALWAYS facing down, toward the bottom--NOT out to the side or towards the top. Also, the transistors are fine, but they're kind of small. It sometimes helps to make them about the same size as the resistors, and even maybe with a circle around them. Also, lines crossing each other like '+' generally mean they're not connected. Putting a dot wherever one line is connected to another means it is connected. That is very important.

 

[audioguru]

Your circuit has the Reset pin 15 floating on the CD4017 instead of connected to 0V.
You should add a "power-up reset circuit" so that the CD4017 is reset when its power is turned on.
You have two resistors powering the LED instead of just one.

 

[Reloadron]

Looking at your cartoon (quite good for using paint) I think I see a problem. You want the 4017 to count to N and halt. Now the 4017 will sequentially make each output high while all the others remain low. You will inhibit the count by making pin 13 high. The way your drawing looks using pin 11 (output 9) to inhibit the count when out 9 goes high all the other outputs will be low. The count will stop with all outputs (except out 9) low. I think you would want pin 13 tied to output 8 pin 9 to get the effect you want. The 4017 will also drive small LEDs direct without the need for a transistor. Not a bad thing I just see no need. Also it looks like outputs 4 & 8 go through a resistor to ground? I don't get that part.

<EDIT>

Plus what AG mentions as to pin 15? I missed that.

</EDIT>

Ron

 

[DerStrom8]

Wow, I guess I missed a lot! Sorry about that. I guess I didn't look close enough at it than I should have. Sorry for my mistakes

Regards

EDIT: I just took another look. I'm sorry if someone already mentioned this, but the way you have it set up now is that the LED is connected directly to +V through two resistors. The way you have it now, you'll always have some power going to the LED, and you don't want that. Also, we really need some resistor values. Without them, it's difficult to say what exactly it will do.

 

[audioguru]

..... the way you have it set up now is that the LED is connected directly to +V through two resistors. The way you have it now, you'll always have some power going to the LED, and you don't want that.

The resistor connected directly to the LED is not needed and can be replaced with a piece of wire. Then you can see that the LED is turned off by the transistor shorting it which wastes power if important.

 

[DerStrom8]

I just took a little bit of time to throw together a basic schematic showing how things should be connected. I did leave out some of the main circuitry, assuming you know how to connect a 555 in astable, and the basics of the 4017. I also left out the reset-upon-power-up that AG suggested. This is just the very basic version. Keep in mind this is not complete! You will still have to do some work. This is just showing how to connect the LEDs to the 4017 through diodes, and how it stops on the last LED. When the last output (and LED) turns on, it causes the transistor to conduct, holding the 555 in reset. As long as it's in reset, the timer will not run. You'll need to put in the power-up reset circuitry yourself. Since this is a school assignment, I really shouldn't show you any more than this. Do some research. Google is your friend--you'll learn a lot about how these chips work.



If I've made any more mistakes (I know I am nowhere near perfect--I still make a lot of those ) I trust you guys (AG and Ron) to point them out

Regards,
Der Strom

 

[audioguru]

Can you imagine what an old lady driver will do when the brake lights on the car ahead of her begin flashing?
She might have an epileptic seizure and step on the gas.

 

[DerStrom8]

Can you imagine what an old lady driver will do when the brake lights on the car ahead of her begin flashing?
She might have an epileptic seizure and step on the gas.

I thought of that as well, but I put away the epileptic seizure part because anyone with epilepsy probably shouldn't be driving anyway

But that's why I talked about safety in, I think it was, my third post. I told the OP that it is unsafe, if not illegal, to modify your brake lights like that, and he assured me this wasn't actually going on a vehicle. It was just an experimental school project. I don't think you have anything to worry about.

 

[SimonFrisendal]

Thank you Der Strom, AG and Ron for helping. This is way more help than i had thought of. I can definitely continue on from here by myself. Thanks alot for everything

Simon.