Homemade LED *hard core electronics*

[Buurin]

I'm here to share what info I have came up with so far on my quest of going all LED, and the homemade units that I built. Contains hard core electronics talk.

First, some background.

After buying a pair of barrel-type 20 LED bulbs off ebay and used it across my two cars, I'm totally sold on going all LED. So I looked at how I can make my Camry so.

First stop is the light failure sensor. My grand goal is to mod it so that it will still sense a bad bulb while being able to not trip on a pair of good LEDs while still sensing one being dead, so I traced its circuit starting from the (99 Camry) EWD PDF I downloaded. Turns out to be very intricate involving a ASIC (I suppose because no datasheet is available on that Toshiba chip). Did I mention this piece costs C$320 from the dealer? And a similar circuit built from
324 op-amps and a resistor network may not fit in the little sensor housing. Too much work. So I just pulled pin 4 out of the plug and called it a day, and in goes the two LED bulbs.

Now the turn signals. I know I need to conquer the flasher. For now I pulled the flasher off cam and took the flasher from Little Pig to do work while I study the former. The flasher comes with an adapter cap, with which I can use either ISO or JSO flashers on our cars. Both flashers and the adapter are interchangeable between gen 4 Camrys and gen 8 Corollas.

This is a much smaller circuit, but still with a odd purpose-built IC - thankfully there are a few similar chips on the market with datasheet. They are available for Atmel U643(B) and ST L9686. But a snag - the exact chip used in the flasher is neither, but they are similar enough that I managed to trace it out and understand how it works, and more importantly, allows me to formulate a plan to reconfigure the PC board to take a 555 timer chip instead.

After hacking the flasher I can go LED on turn signals. Now I need a pair of 3156 in the back and a pair of 3157 in the front, all amber. Again I want the barrel type for front (look at your gen 4 front corners and you'll know why), but the amber 3157s are too expensive.

My savior comes when I discovered that Active Surplus is stocking lots of 6000mcd 4-legged sqaure LEDs in amber and red, at 5 for $1 . And the same ebayer now sells the exact same bulbs that I bought at $8 a pair! Time to buy another pair and stock up on those LEDs. Bought 20 last Saturday, came home, and found 3 of them to be red . No problem, I'll find use for them. Bench tests shows that they drop 3V and can reliably withstand 85mA. Light up 3 of them together and it's enough to light up my room's ceiling. Time to buy another pair at $8.

My plan is now to hack my flasher to run a 555 instead. Hopefully the relay coil will not take more than 200mA; I don't think I have enough space to add a transistor. I figured that 1k and 180k resistors plus a 3.3uF cap, assembled as a standard 555 oscillator circuit, will give me 92 beats/min, close enough to 85 beats/min of stock flasher.

If this works, I'll get a auto-spec SA555 for permanent use.

I also have some 9-LED 921 bulbs on order. Once done I'll have full LED tail in no time.

To be continued.

[hiace24]

Are these leds the 1w luxeons?

[Buurin]

Originally Posted by hiace24

Are these leds the 1w luxeons?

Now that you mentioned it, I'm not sure. I checked and they looks like Philips SuperFlux. Then again a lot of other LEDs look the same. I'll need to drive them at 70mA and check the voltage drop. Anyways I don't think they put out anywhere near one watt.

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I took the flasher apart and confirmed that the coil uses 110mA. So I am golden. Two more diodes to protect it from reverse bias and I'm ready to hack.

Except one thing. I hooked the now naked relay to my breadboard prototype circuit and see a noticeable delay once I applied power before it would flash regularly. Anyone know how I can eliminate that?

[BlueFusion6851]

Nice... be sure to upload lots of pictures too!

[89yotarollagts]

so whats the moral of the story... are you trying to wire the car up so your blinkers dont flash twice as fast due to the lower powered LED bulbs ?

[Buurin]

Originally Posted by 89yotarollagts

so whats the moral of the story... are you trying to wire the car up so your blinkers dont flash twice as fast due to the lower powered LED bulbs ?

Exactly. No way I would use load resistors which defeats the whole purpose of going all LEDs.

I'm trying to wire the blinker up so that it doesn't flash twice as fast. I should not need to touch anything on the car except changing the actual bulbs for LEDs.

[89yotarollagts]

ive been wanting to change over to LED's since i put them in my dash, but i understand what you are talken about,, if you run only 3 bulbs on the blinkers they flash like mad...

[Pineapple]

The load resistor doesn't really defeat the propose. Signal are not on 100% of the time. It doesn't draw current until the bulb is on. Some car need the load resistor for cruise control on brake light.

[Tommy]

wait....i thought the purpose was to have the look of LED's, your purpose is to have LED's and use less power in the car?? wow..............

[Pineapple]

Use less power and last longer.

[89yotarollagts]

^ read the other posts.. "the moral of the story" Led's use less power, so when you replace the OEM bulbs with LED's your blinkers Flash twice as fast as they should, which is probly illegal in some states, this is what buurin is trying to cure..

[touringcamry]

So if I understand this correctly, you will be using the 555 oscillator to control the flashing so you'd need a constant output from the flasher circuit or blinker relay right?

How are you building this? Are you soldering a bunch of LEDs to a breadboard that will fill the entire compartment or are they going in the same place at the original bulbs?

[Tommy]

Originally Posted by 89yotarollagts

^ read the other posts.. "the moral of the story" Led's use less power, so when you replace the OEM bulbs with LED's your blinkers Flash twice as fast as they should, which is probly illegal in some states, this is what buurin is trying to cure..

no no, you can just use a resistor to match the resistance of the normal bulbs and accomplish the same thing, he's doing all this work to use less power AND not have it blink fast. Not sure why he's worried about less power, but hey...why not huh?

[6 Brzina]

Why do all that wiring when you can just pop the LEDs in the sockets and buy an electronic flasher to replace the stock one? I did that with my old work truck because the turn signals actually flashed to slow (a lot of blubs), put one of those on there and problem solved. It flashes the bulbs at the same speed no matter what the current draw of the lights are. Also if one burns out it doesn't start flashing real fast, just stays at the same speed.

[Buurin]

Originally Posted by 6 Brzina

Why do all that wiring when you can just pop the LEDs in the sockets and buy an electronic flasher to replace the stock one?

I'll admit... I'm too cheap to pay $19+shipping for an electronic blinker. I have all the parts I need to hack an 555 oscillator circuit into the OEM blinker.

All that wiring will give me a blinker that never blinks fast. Work is on the blinker; nothing is being done on the car itself.

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Now I know by jacking up the voltage of the negative leg of timing cap using a 2-resistor voltage divider will (mostly) eliminate the first cycle delay. Upper 1.5k/lower 1.0k works best. 15k/10k also seems to work. But now my relay coil clicks REALLY fast as in buzzing. Does it mean my 555 is not proving enough current to drive it?