My own integrated LED tail light

[DownrangeFuture]

Okay, so I've been looking at integrated/LED tail lights and my complaints are always that they're stupid expensive, or you don't know just how good the components are, and build quality is suspect 'cause you're buying it from some guy in China off fleabay. So I think to myself, "Self, you solder components and dissect schematics for a living. Surely, it wouldn't be too hard to build one yourself."

So I designed one. I was that bored at work.

I decided that I needed some sort of voltage regulation. Most of the ones I've seen (even the $150 ones) seem to be lacking in that area. While the voltage shouldn't change, anyone who has worked in electronic repair for more than 5 minutes knows that weird stuff happens. I also wanted a simple way to make them integrated. I was keeping the red lens so I'm just flashing that side on and off.

Anyways, here's what I have designed so far. The diagram is 4.5"x1.5" and should fit in my tail light right in front of the reflector. I haven't nailed down the exact outside shape, but since they'll cut whatever shape for free, and I haven't decided on a professional PCB or a radio shack special. I figure that's good for now.

And for you nerdy types, here's the scat I'm working with. I think that the voltage coming in might be negative, if so the transistors would have to change to PNP type, and the collector and emitter would swap. Ground would be on the collector then. LED's are white 140deg/3.4Vdc forward/20mA. Resistors are all 10ohm @ 0.25W. Transistors are TIP29A the TI PNP equivalent.

Anyway, anyone see any issues with building this? Mostly on the schematic/wiring side. I know I could wire this up.

EDIT: I caught a big one. I calculated this at 24VDC for some reason. It should be 12. The regulator would make the voltage stay at 12 with the brake on, but would allow the current to increase. But without changing the resistance in the circuit, it won't change the current draw either way.

Back to the old drawing board.

 

[DownrangeFuture]

This one should work. I lost the integrated thing, but that was more along the lines of "it'd be neat if" things. I guess if I really wanted it to flash, then I could run two of these circuits.

 

[Amorousnerdium]

Why not replace the left and right LEDS with bicolor LEDS and trigger the second color for blinkers?

Also, refresh my electronics engineering for a sec, what is D1 being used for?

 

[DownrangeFuture]

Doh, it's always the simple solutions that escape me. Since the LED's are in parallel, it'd be trivial to remove a few branches and run those as the flashers. My deal with the color was I'm using the stock lens. So red. I never was good with mixing colors. :lol:

D1 forces the Brake line to use the smaller resistor only. The running light line uses both resistors in parallel and so winds up with a resistance less than the value of either resistor. So the current is less with just the running light. Except now that I think about it, I did that backwards. The running light and brake light lines should be swapped. It's been rattling around in my head for a few days now. Even now I'm like, "Maybe I could..."

I actually think this would work better. 12 volts across just the 100 ohm resistor and then when you hit the brake, it turns the transistor on and you get the whole parallel array. Thus lowering the current across the resistors allowing more current for the LEDs. I'm worried about my math on the resistors (R1, R2), but I'm way too tired to check them right now.

 

[Amorousnerdium]

Ah, ok.

Are Q1 and Q2 still TIP29A?

 

[DownrangeFuture]

I went with BC547 and BC337 respectively. TIP29A should work, but was cutting it close on the HEF.

 

[Amorousnerdium]

Do you have an updated pcb layout diagram? I have a design in Altium that I am working with now with a few added features myself.

It would be nice to get this designed into a simple printable pcb bored that would work with the radio shack kits that anyone can use.

 

[DownrangeFuture]

Not yet. I'm working on it cause that was my goal, to build my own and have all the info up for people to do their own. Or buy one from me or something. Not that I'm into starting my own business, just that not everyone can solder.

I'm still working out the details on the new schematic. Apparently I'm running too much constant current through the transistors right now. I just noticed that I should be pulling about 360mA constant current and the collector of Q2 is only rated for 350mA constant.

I should have a design knocked out by Friday hopefully, and I'll post the finished PCB layout then too. Then I'm ordering parts and hashing out the final details. My hope was to at least get the parts list up for people with scats and the PCB diagram. Maybe get a whole group order together of the PCB or something. 3 boards cost $178 or so, (red solder mask, silk screen top, 2 layer board) but each additional board is only about $1.80 so the more boards you order at once the better.

Anyway, I'll keep the thread updated as I go. Promise. I just thought I was done with design or I wouldn't have started the thread yet. *sigh*

 

[Cloggy]

Do you have electronic workbench or something similar? you can generally check it that way. Or make a simple design, half the leds are rear lights and the other half switch on when you brake (placed inbetween each other). Sorry not trying to tell you what to do just trying to help.

BTW I was on a course at NAS Jacksonville about 9 years ago.

Sorry off to bed now, its gone 1 in the morning here, i'll take a look in tomorrow.

 

[DownrangeFuture]

I started that way, with the half on at running and all at brake, but I decided that I wanted all of them on all the time.

I'm mostly done with the scat and PCB. I'm going to buy the parts here in a day or two and wire to a breadboard to test it out. I'm not paying that much to prototype when I don't know for sure it'll work. lol. I managed to get the flashing back in, it should wig-wag with the stock-style blinker.

When I get it all done (and tested) I'll get the scats and pics of it working up here. Or if it blows up and catches on fire, I'll post that video too. lol. Then it's off to a prototype PCB.

EDIT: Oh yeah, I have a nice workbench at work. And I've pieced together a passable one at home. My first one will probably be done at work. I even have 12VDC test power supply at work (and fire extinguishers, lol). The rest will have to be done at my house. But I'm running the PACE mini solder station at home. The three channel one that does everything sans micro-chine.

 

[DownrangeFuture]

Okay, so I hope I'm all done. At least with the paper part anyway. This circuit will run all the LEDs at two current levels. 6mA for the running light and 20mA for the brake. I calculate the brake intensity as 720cd (if you're using 70deg 22000mcd LEDs). That should be daylight visible. Also running a lower current at the running light will extend the life of the LEDs. The voltage controller will protect against voltage spikes (and consequently current spikes) and should help prevent blowing LEDs if there was a surge for some reason. Like, idk, starting the bike...

When the turn signal is activated, the half of the brake will turn off. So it will wig-wag with the stock flasher.

I plan to start a prototype with a breadboard here in the next couple of days. I'll update with the results.

And here's the BOM.

D1,56 1N5819 DIGIKEY 1N5819FSTR-ND
D2 - D55 Any color, bright/20mA typ/3.4Vdc @ test/T-1 style
Q1/Q5 BC547 DIGIKEY BC547CGOS-ND
Q2,6 TIP31A DIGIKEY 497-2602-5-ND
Q3,4,7,8 TIP29A DIGIKEY 497-2580-5-ND
R1,4 2.2K OHMS
R2,5 11 OHMS DIGIKEY CMF11.0HFCT-ND
R3,6 5 OHMS DIGIKEY WHA5R0FECT-ND
U1 LM7812 DIGIKEY LM7812ACT-ND

 

[Cloggy]

It sounds like you've got all the right equipment. Hope everything goes as planned on the breadboard.

looks like you've worked it out well, looking forward to seeing the finished product :thumbup:.

Another way to control the brightness of the LEDS is with a PWM, but this is a few components extra.

 

[DownrangeFuture]

The parts will be here mid-Feb so I'll get an update then. I couldn't turn down the LED's on fleabay for $8 with free shipping. 120deg at 20Kmcd. They may be crap, but it's just for the prototype. 100 pcs 5mm Flat top white LED Wide Angle Light lamp - eBay (item 110609483178 end time Feb-06-11 21:11:53 PST) So I'll let you guys know if they're any good.

I also noticed I forgot the ground that's supposed to be on the bottom left corner of each circuit, and Q4 and Q7 aren't right. Pin 2 should just be inline with that run, pin 3 should be only connected to ground, and pin 1 is right. That would short the circuit to ground when the blinker turns on. the way it's wired now, the light will ONLY be on when the blinker is actually on. Yikes. Actually, a buddy of mine at work caught it all.

But anyways, see you in the second half of Feb!

 

[Chaosratt]

The parts will be here mid-Feb so I'll get an update then. I couldn't turn down the LED's on fleabay for $8 with free shipping. 120deg at 20Kmcd. They may be crap, but it's just for the prototype. 100 pcs 5mm Flat top white LED Wide Angle Light lamp - eBay (item 110609483178 end time Feb-06-11 21:11:53 PST) So I'll let you guys know if they're any good.

I also noticed I forgot the ground that's supposed to be on the bottom left corner of each circuit, and Q4 and Q7 aren't right. Pin 2 should just be inline with that run, pin 3 should be only connected to ground, and pin 1 is right. That would short the circuit to ground when the blinker turns on. the way it's wired now, the light will ONLY be on when the blinker is actually on. Yikes. Actually, a buddy of mine at work caught it all.

But anyways, see you in the second half of Feb!

Dear god. Grabbed 1 each of his 100 packs for amber, red, and white for my future projects and added him to my fav ebay seller list. $8 SHIPPED from China? Yes please, I don't care if half of em are junk, thats still a fantastic deal.