Led Sequencer circuit help

[djohnso]

This is my first post. Additionally I have little experience with building electronics.

Please forgive me if I’ve posted this to the wrong place.

I have designed a circuit that hopefully sequentially lights eight LEDs for a right or left turn signal. When the break is applied it lights both sides sequentially. The typical light sequence should be:
D1
D1, D2
D1, D2, D3
D1, D2, D3, D4
D1, D2, D3, D4, D5
D1, D2, D3, D4, D5, D6
D1, D2, D3, D4, D5, D6, D7
D1, D2, D3, D4, D5, D6, D7, D8
The circuit remains lit until the turn signal input goes low (this kills and resets the circuit).

The sequence from D1 to all 8 LEDS being lit will be quick (approx 1/2 time of flasher on).

Hopefully I have attached a schematic of my circuit below.

I need an electronics brain to calculate the total power draw, advise of any overloaded/stressed components and generally point out this novice in the right direction.

I want to use off the shelf stuff (no programmable ICs) to build this circuit. The reason for this is simple; I need to build this circuit, I would prefer not buy equipment and learn to program ICs.

Thanks,

David Johnson

 

[djohnso]

 

[(*steve*)]

Does something break when you apply the brake?

Firstly, how do you prevent the quite variable and noisy 12V in a car from disrupting your circuit?

Secondly, what is the purpose of all the 12v zener diodes? Did you design this yourself? They seem to be connected the wrong way around anyway (if they're being used as zeners). Do you understand what a Zener diode is?

Do you want the LEDs to get progressively dimmer as more come on? R1 and R2 will give you a maximum current of around 1mA for a single diode, or 0.12mA through each of the 8.

1mA is already so low that you'll barely see the LEDs at night, and certainly not during the day.

At this low current, connecting the LEDs effectively in parallel is not going to be a real issue, but the LED current is unlikely to be evenly spread. You need a lower value resistor in series with each LED so that the current for each is independently controlled, and not shared (perhaps unevenly) between them.

The shift register is an interesting, but unusual choice of device to perform this task.

I have not looked at the circuit in detail, but you would need to ensure the device gets a reset signal which I can't see you providing.

I would probably look at an LM3914 -- it seems to be the obvious chip to use. You can simply charge a capacitor from a constant current source (and even that may not be necessary). You will need some magic to discharge the capacitor when the turn or brake signal disappears, but that's not too hard.

 

[Laplace]

Not sure what the purpose of the 12v zener diodes would be. They all seem to be forward biased but a zener diode is only useful when it is reverse biased. Perhaps an ordinary rectifier diode would be more appropriate for your circuit.

Are those yellow LEDs rated for 20 mA current? Are they intended for use in a real vehicle? If so, then they may not be bright enough to be seen well in sunlit conditions. Not to mention that your circuit does not drive them with anywhere near 20 mA current. If this is 'for real' then you may need to rethink your selection of LED to something more potent (1 watt LEDs @ 300 mA?)

When you label the source voltage as 'turn signal' or 'brake signal' are you tapping the voltage from across the existing filament bulb? If you draw power for the LEDs from the existing bulbs, then the additional current drain may upset operation of the flasher (not your current circuit, of course, but if you use more potent LEDs...). In that case you would need to draw current from a switched power circuit and use the voltage on the 'signal' lines as a low current control signal.