Ok good luck. Let me know when finished. When first ( basic set-up) works I will send you the rs232 part.
building it step by step.

 

Can ULN2803 input operate safely above 5 volts?

 

Can ULN2803 input operate safely above 5 volts?

Please read data sheet

 

Minke one of these for each segment of LEDs.

The chip is an NE555 or similar timer chip.

The MOSFET transistor is a 2n7000 or similar low current mosfet. (Lower right)

The PNP is any small PNP transistor (e.g. 2n4403, 2n2906, 2N3906)...

This one stays on for about 2.5 seconds. Increase the resistor that is currently 22k. Any value up to 470k should give you a proportionally longer response (220k will give about 25 Seconds).
If you need longer than 47 seconds, you can use a bigger capacitor for linear response as well.


View attachment 98577

Why the MOSFET? The 555 can't drive 30 mA?

See attached. +12 V in to start it. LEDs returned to ground, not +V. I haven't built it yet but it should be pretty close to a working idea. No programming required. Maybe $1.00 worth of parts for each circuit. Rear window turning signal?

(edited as an afterthought)
Maybe capacitor couple the trigger input?

 

Why the MOSFET? The 555 can't drive 30 mA?

If he wanted to put 3 HBLEDs in series, that would be 3 x 3.3 V = 10 Volts. The 555 is specificed to output Vcc - 2 volts. OP asked for 12V supply and that would be 12 - 2 = 10 volt output. This gives no overhead for current limiting and possibly glitching output.

I guess he could use 2 strings of 2 LEDs in parallel for 4 LEDs per segment but it was also an image I had from another post. Last I read of this string, he didn't want the 555 option anyhow.

 

If he wanted to put 3 HBLEDs in series, that would be 3 x 3.3 V = 10 Volts. The 555 is specificed to output Vcc - 2 volts. OP asked for 12V supply and that would be 12 - 2 = 10 volt output. This gives no overhead for current limiting and possibly glitching output.

I guess he could use 2 strings of 2 LEDs in parallel for 4 LEDs per segment but it was also an image I had from another post. Last I read of this string, he didn't want the 555 option anyhow.

I assumed simple red LEDs, but if it isn't what he wanted anyway I guess it doesn't matter. The 555 was a good idea. Much cheaper and easier. And lights driven from ground, like an automotive system in case he wanted to use a kosher light bulb.

 

I assumed simple red LEDs, but if it isn't what he wanted anyway I guess it doesn't matter. The 555 was a good idea. Much cheaper and easier. And lights driven from ground, like an automotive system in case he wanted to use a kosher light bulb.

Yes, good point. I forgot about the grounded connections of automotive. A high-side switching design would have been better.

 

ULN2003 and 2803 are designed for 3 to 6 V input but can handle 12 V. The 2004 and 2804 are designed for 6-15 V input and can handle 24 V.

ak

 

Please read data sheet

Already did. The answer is above 6v no.
But that is the p/n used in your 12v circuit.