5 scrolling arrow indicator

Hi there, I'm new to this forum and am having a bit of trouble with a project.
I'm making custom LED tail lights for my car, and I need help with making a scrolling indicator. I know how to wire up basic leds with resistors, but unfortunately didn't pay much attention in highschool as to how transistors/timing circuits etc work.

This is a simple animation of what I am looking to accomplish with your help.

**broken link removed**

I need each "arrow" to be a 12v channel, I've worked out that I need a 14 ohm resistor for each channel (so closest actual resistor is...16 ohm?

It's probably such a simple request, but I've tried looking all over the net, I've found similar circuits and they said you could modify the channels with transistors but, I'm not that good with electronics.

Any help would be greatly appreciated!

This might help:

**broken link removed**

It looks like it would help, although I honestly don't understand half of the stuff it is talking about. I understand when its talking about "grouping" the LED's through gates but thats about the limit for me haha. It said on the page that it can run higher current loads...is there any way to tell if it can run 12v per output or if you can use selective outputs (eg instead of it running through all 10 it only runs through 5)?

You can short-cycle the 4017 counter by feeding back the first unused output to the Reset pin. For example, if you want only five leds, you would used the decoded OUTPUTs 0,1,2,3, and 4. Output 5 would get wired back to RESET, so the counter recycles back to OUT0 after OUT4 (five states).

Note that the 4017 will barely drive one 20mA LED per OUT pin. For your application, you probably need >100mA per arrow segment, so you will need a driver consisting of a transistor (or something else) between the 4017 pin and the clump of LEDs in the segment.

According to the 4017's datasheet it will run on 12v which is a plus for you, but Im with Mike about needing a driver for your LEDs. I would recommend using a FET instead of a transistor for switching your load, with a similar circuit as this (replacing the LED in the circuit with your cluster of LEDs, and the switch with the decade counter):

**broken link removed**

It is illegal in Canada to tamper with factory lighting on a car. Kids modified the lights on their cars and could not be seen at night and could not be seen at an angle so the cops have a good time impounding the cars.

What makes you think anyone cares what you laws are in Canada - how does that help the OP with his question?

SirKitBreaker said:

What makes you think anyone cares what you laws are in Canada - how does that help the OP with his question?

Click to expand...

On another website they ban discussions about illegal things.
On this website we don't want somebody to modify their car's rear lights then have him rear-ended because the lighting was wrong.

BUT maybe you are the kid I saw yesterday with all the rear lights on your car "blackened". I could barely see the lights but noticed that one stop light was burned out. The windows were also black. If the police caught you then you won't have your car for a while.

audioguru, as far as I remember, the MTO requires lights on cars to be visible from a specific distance, but Im pretty sure tinting your tails is legal.

/ot

my states laws require my tail lights to be visible from 200 meters away, with 30 running red 6000mcd LEDs per tail, and another 25 16000mcd for brake, 10 25000mcd white LEDs for reverse and 5 arrows of 5x 25000mcd amber LEDs for my arrows.. it will be more than visible, even with a 50% tint, probably blinding..so i might put a pot on them :/...the indicator has to flash faster than 60bpm, i checked with my regulations and scrolling between arrows counts as flashing. all of my LED's have a range of up to 65% at 70degrees in any direction.

I'm in Australia, and unless my car was shipped overnight to Canada and back the next day while someone took it for a test drive, I doubt it was me.

I've already put through the proposal to regency (regulations commission) and they said its perfectly fine and visible, not to mention this is mainly for a show car.

Back on topic, ParkingLotLust,

The circuit you described, is that basically (from what i understand, remember I'm a complete novice at this) the output pin on the decade counter serves as a switch to a separate 12v circuit (your circuit) for each "arrow"? Also, in the circuit, if I was connecting this to each output pin..would I need a diode, seen as its got a power supply on it?

Thanks MikeMI for clearing that up too.

I am glad to hear that you thoroughly researched the laws in your area about car lighting.
I hope a Canadian kid does not copy you then lose his car to the police.

Each segment of an arrow uses an output from the CD4017 which drives its own Mosfet.

Electronic circuits in cars must be protected from 60V spikes on the 12V that will destroy most of your circuit.

I still don't understand how a mosfet/transistor works.. I know it's a gate of some sort, I believe it is anyway, and how do i know what type of mosfet i need?

The Mosfet in the schematic is an N-channel one (not a P-channel one). It must be able to conduct as much or more current that is needed for the LEDs.
Most N-channel Mosfets turn on completely when the gate is 10V (to 20V) more positive that the source which is grounded in the schematic. The Mosfet turns off when its gate voltage goes to near ground.

Hi individual,

as I see you haven't got a circuit suggestion yet.

Here is a circuit suiting your needs.

IC1 (NE555) is an astable multivibrator oscillating at approximately 60Hz (58Hz). It clocks the counter IC2 (HCF4017) which is a decade counter (Johnson counter).

Outputs 2 through 6 switch on the N-channel MosFet transistors which in turn switch on the connected LED chains. When the counter reaches count 7 it resets automatically and restarts the sequence.

The BS170 has an On-resistance of 1.2Ω which you should consider when calculating R13 through R17 for the LEDs you are going to use. The transistors can handle currents up to 500mA which is safe for an LED chain of normally 20mA.

PCB dimensions: 87X47mm (3.42X1.83")

BTW, there are no specific laws in Thailand prescribing car lighting. Tuk-tuks (agricultural trucks) use tail-lights consisting of obsolete CD, nailed to the rear end.

If somebody runs into such a vehicle he is responsible for the resulting damage. Traffic law1 in Thailand prescribes to keep the eyes open while driving.

Regards

Boncuk

Boncuk, what is the purpose of the 100Ω resistors at the gate of the MOSFETs?

Mosfets ring or oscillate at a VHF frequency which makes them very hot if they do not have a low value resistor (10 to 100 ohms) in series with the gate mounted very close to the gate pin.

Thanks heaps Boncuk! Do you have this file in Protel, Altium, Eagle or Gerber format? I need one of these to get it manufactured. Thanks heaps! I'll be sure to update you on the project as it comes, all of you, so you can see what your help turns into!

MikeMl said:

Boncuk, what is the purpose of the 100Ω resistors at the gate of the MOSFETs?

Click to expand...

Besides audioguru's explanation I guess it's good practice to use a low value gate resistor when controlling MosFet transistors.

They won't hurt or cause malfunctions.

Regards

Boncuk

individual said:

Thanks heaps Boncuk! Do you have this file in Protel, Altium, Eagle or Gerber format? I need one of these to get it manufactured. Thanks heaps! I'll be sure to update you on the project as it comes, all of you, so you can see what your help turns into!

Click to expand...

Hi individual,

I will provide Eagle files for you. Just PM me your email address. (Download Eagle for your OS from CadSoft Online: EAGLE Layout Editor)

When taking a close look at the PCB layout I guess it can be shortened by at least 15mm when placing parts a bit closer.

I'll rework the design leaving it purely single sided.

Here is the altered design. Attachment shows the silk screen. Board size is now 75.5650X44.7675mm (2.9750X1.7625").

Regards

Boncuk

As a novice to electronics, why would it be preferable to use a mosfet rather than a standard N transistor?

Angie