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Help With Sequential LED 3rd Brake Light. Answered

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
76543211234567
76543211234567

I have a pic programmer and an Arduino Uno.

Any ideas?

Thanks in advance!

Discussions

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

Steve

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?

Thanks!

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

Steve

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,
-Tim

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.

Steve

+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.

Steve

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.....

Thanks

Steve

i was thinking a relay to the light would be the best way to get it to start the "pattern".