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Programmable Third Brake Light Flasher - PIC12F629

Gayan Soyza

Active Member
Here is another Kindergarten project of mine. It’s called programmable third brake light flasher. Looks like simple but need to think in all round.

Operation
When brake is applied the circuit will flashes the third brake light couple of times & stays continuously on until the driver releases the brake. This will make other drivers attention due to the flashing effect with a safety manner.
Number of flashes, flash on time and flash off time can be adjust by the user with the two buttons.

Here nothing is illegal so I didn’t get a problem. Also this is not for commercial I did just for fun.




This circuit designed for LED third brake lights & not for incandescent (filament) third brake lights.

I got several problems when calculating the pulse delay for incandescent bulbs. Because these bulbs take time to switch on & off. They won’t accept high speed switching. It’s easy to calculate a long delay but if the PULSE OFF DELAY time is too long in a traffic condition it will meet some problems. If the pulse delay time too short it won’t show you the blinking effect because of poor turning on time with these bulbs. So I escaped from incandescent bulbs. Modern all automobile lighting systems using LED’s. So I also shifted to high speed LED’s.

The delays are calculated to the best timing parameters. Can use all this calculated delays in the table without any problem.

The Zip file contains how to adjust routine.
 

Attachments

kchriste

New Member
Forum Supporter
Nice graphics. It would be funny if the 12F629 was thinking it was 12F675 or a 18F series chip. Dream on little PIC. :D
On a more serious note, I think your off time of 0.04s is a little too short but since it will be adjustable it is probably not an issue.
Kudos on the professional presentation!
 

Gayan Soyza

Active Member
Thanks Kchristie

I tested on many delays. It took me lot of time to calculate what’s the best delay range.

Also with some of the above delays bulb doesn’t have time go fully off it looks like dimming if you reduced to the minimum delay with some bulbs. The maximum off delay is upto 0.05 seconds adjustable so can see the bulb going fully off. So I got advantage from it.
 
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Nigel Goodwin

Super Moderator
Most Helpful Member
It's to ensure the TIP41 turns off fully, otherwise any slight leakage in the driver might keep it switched on.

It's good practice to include such resistors.
 

bananasiong

New Member
This resistor is needed for what type of configuration? Emitter drives base type? Or for those common emitter type switch?
Can I know where the leakage from that causing the transistor for keeping on? I don't see how the TIP41 is turned on if the 2N2222 is not turned on.

Thanks.
 

Ambient

New Member
"kindergarten"? Is this going on a real car or a Power Wheels Hummer? Unless you mean because it's a basic circuit. Either way, this would be a good idea for one when it is running. Good safety gear. But I would rather just attach a 30' cable from the kiddies vehicle to the house lol.

I have seen some modded brakes lights on youtube. One guy has a full width brake light on the trunk, and imitates a cylon visor. But I am not sure if they are still legal in the US as long as they do not flash. But you can try that kind of thing if you get a bigger PIC. And a load of LED's from http://alan-parekh.vstore.ca/
 

Nigel Goodwin

Super Moderator
Most Helpful Member
bananasiong said:
I don't see how the TIP41 is turned on if the 2N2222 is not turned on.
Like I said in the previous post, if there's any slight leakage in the driver (the 2N2222) it might switch the TIP41 on - at least partially.
 

Gayan Soyza

Active Member
Hi bananasiong

Nigel already points outs what’s the purpose of that 1k resister. It’s to ensure that the power transistor is fully off.

Some addition points

The 1k resistor on the base will have an effect on the current required by the base to turn the transistor on. So it increases the required base current. If no resister it will turn the transistor on with a few uA. Most of the current delivered into the base is lost in the biasing network. Darlington pairs have built in these resisters.

Also note that when the load increases the transistor gets hot. Sometimes it tries to get latch due to heat so the 1k resistor turns off the power transistor even if heat tries to keep it turned on.
 

Gayan Soyza

Active Member
Ambient said:
I have seen some modded brakes lights on youtube. One guy has a full width brake light on the trunk, and imitates a cylon visor. But I am not sure if they are still legal in the US as long as they do not flash. But you can try that kind of thing if you get a bigger PIC. And a load of LED's from http://alan-parekh.vstore.ca/
Hi Ambient your link is not working.I want to see that I cannot wait anymore :D
 

eblc1388

Active Member
Nigel Goodwin said:
Like I said in the previous post, if there's any slight leakage in the driver (the 2N2222) it might switch the TIP41 on - at least partially.
Don't worry about leakage. The circuit is good for one off operation only as the TIP41 BE junction will burnt out immediately when the 2N2222 turns ON.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
eblc1388 said:
Don't worry about leakage. The circuit is good for one off operation only as the TIP41 BE junction will burnt out immediately when the 2N2222 turns ON.
:D Good point, the diagram is missing a resistor in the emitter of the 2N2222.
 

bananasiong

New Member
eblc1388 said:
Don't worry about leakage. The circuit is good for one off operation only as the TIP41 BE junction will burnt out immediately when the 2N2222 turns ON.
Is that because of the emtter of 2N2222 is not current limited? What if the collector of 2N2222 connected to the collector of the TIP41 to form darlington?
 

Gayan Soyza

Active Member
Doesn’t the inbuilt collector & emitter diodes of 2N 2222 helps to drop down the voltage below 5V? & also data sheet shows TIP41’s maximum base current is supports to a bigger value.

Now already two weeks continuously running in a damn hot environment no more problems occurred.

Anyway I like your ideas thanks for that guys.
 

kchriste

New Member
Forum Supporter
The emitter current in the 2n2222 will be limited by the Beta of the 2n2222. This will vary with different 2n2222s. So it would be best to eliminate the 120R resistor in the base and put a resistor in the 2n2222s emitter lead instead. Choose the emitter resistor so that the TIP41 will saturate properly for the given load. Or get rid of the TIP41 and 2n2222 and replace them with a TIP121 instead.
 
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Ambient

New Member
Gayan Soyza said:
Hi Ambient your link is not working.I want to see that I cannot wait anymore :D
That is odd, the link works fine for me. You can try getting there by clicking their advertisement on hacked gadgets website: http://hackedgadgets.com/

The ad is on the left side. This guys prices are half of the next best price I can find (moreleds.com). Good customer service, too.
 

bananasiong

New Member
Hi,
That link worked for me too.
Back to the question, if the connection is as kchriste suggested, then where should the 1 k:eek:hm: resistor be? Is the connection in my attachment correct?
So basically the resistor that used to prevent the leakage current from turning on another transistor is needed when there are paired transistors?

Thanks
 

Attachments

kchriste

New Member
Forum Supporter
You have it correct, BananaSiong. The 1K resistor helps to offset any leakage caused by the 2n2222 and also any Collector-Base leakage in the TIP41 itself. While these leakage currents are negligible under normal operating conditions, they can become a problem at very high temperatures hence the inclusion of the resistor in a good design.
 

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