Help With Sequential LED 3rd Brake Light.

I am looking for a way to make sequential third brake light on my truck. The light has 28 LED's total, 14 columns, 2 rows. I would like to make it so when I hit the brakes the light starts from the center and moves outward sequentially from the center, but i want them to stay on once they have been light, not just flash. 

This is the order i would like them to light

I have a pic programmer and an Arduino Uno.

Any ideas?

Thanks in advance!

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You COULD do this, all in analogue electronics, but if you want to use a processor, you could do it with 2 of these chips, the TLC59025

There are quite a few makers of very similar chips "serial drive 16 channel LED driver". The chips are serially addressed and controlled. USe the Uno, and I suspect you'll find a driver for it, but its easy enough to "bit-bang" if you need it.

With these things, you don't need to put a resistor on each LED. I suggest you wire your two rows of LEDs, so that they are in common 2 led columns - set your power supply up, so there is the minimum voltage on the chips to get the right brighness. 

I built a special digital clock for an Instructables member recently using them

TJOpitz89 (author)  steveastrouk5 years ago
Thank you so much for your reply. I was trying to figure out a way to do this with analogue electronics, but I couldnt think of what i would use.

I was thinking a 555 timer and a 4017 counter. but then the only way i can think to keep them on constantly instead of repeating would be a relay for every column of LEDs.

Do you think there would be a better way?

No, you could gate off the pulses from the 555 when the counter "overflows", but using logic is quite messy.

Analogue - use two or three LM3914 chips, and use a 555 to generate a ramping voltage to drive them - basically a one shot, but you pick off the capacitor voltage to drive the 3914s

TJOpitz89 (author)  steveastrouk5 years ago
The analogue way sounds like it would make more sense. Does the LM3914 read a specific voltage range? all of the schematics I see for them are for 0-5 volts.

Also, if i used a 555 to generate a ramping voltage wouldn't it repeat making a strobing effect?

(sorry for all of the questions, I am new to a lot of this but I love everything that I have learned thus far.
Thank you,
No, you can adjust the input to suit the electronics. If you make a one shot, or even just charge a capacitor, you should be able to make it stay bright.

+1 Super easy build, especially if going overkill with arduino :) Only difficulty is you need 'always on' power so the duino stays 'booted up' and then just listen for the 12v brake signal...probably a good idea to have it run a relay or optoisolator so the arduino input remains protected from surges.
...or you take off the bootloader code on the 'duino perhaps ? Then the 12v brake signal could (ADD FILTER - good point) power up the chip, and do the brakes, then when your foot comes off, so do the brakes.

Indeed! nixing the bootloader adds complexity and versatility, a delicate balance.
Ooh, caveat I'd missed: You'll need a proper SPI programmer for the processor too.....


TJOpitz89 (author)  frollard5 years ago
i was thinking a relay to the light would be the best way to get it to start the "pattern".