Converting LED Turn Signals into Sequential Signals (Show Only)

gazz

Joined Oct 30, 2009
22
What do i need to do to add more LM3914's olphart's circuit?

playing on breadboard, and got the lights sequencing nicely with one chip, i want to add another 10 led's now and have them sequence.. then another 10 after that,

Do i need to play with the component values when expanding the LM3914's and leds?
 

gazz

Joined Oct 30, 2009
22
I can see i need to connect pin 9 of the first chip to pin 1 of the 2nd,
but what about the other connections? do i need to feed pin 5 of both chips via a resistor and capacitor of their own, or share the first ones,

do i tie the 2nd chips pin 9 to V+ to keep it in bar mode? etc
 

gazz

Joined Oct 30, 2009
22
Think i'm figuring this out,

I used this schematic from sparkfun...

Works beautifully with the input fed via the resistor and capacitor as shown in olpharts circuit, played with the resistor value and got a nice sequence speed for the 500ms on time of a vehicles flasher relay.

i'm going to have a go at running 3 LM3914's now,

i'm wondering about led current, set up like shown above, the led's get just over 7Ma, if i keep the whole circuit running on 5 volts to reduce the volt dropped across the led's (i'll use a buck regulator to drop the 12-16 volts from the car to power the circuit at 5 volts) could i run them at 20Ma without frying the LM3914's?

I could drop the circuit voltage a bit more if it helps?
 
I believe the LM3914 limit is 30mA.

But there are also wattage concerns, so if you are worried you can always glue a heat sink to the chips.

And I would stick with the 5 volts.
 

gazz

Joined Oct 30, 2009
22
Cheers, 5 volts seems to be best then, i could go down to 3 volts i believe so i'm only dropping 0.9 volts across the led's, but im not sure how that affects the power consumption,

I'm wondering about how to set the led current consumption on the individual chips, it's supposed to be the resistance between pins 7 and 8 to earth, is that the same when running 3 chips cascaded? the first 2 have a 1k resistor from pin 7, but the last chip has that 2.2k from pin 7, then the 3.3k to earth, and that's part of what sets the upper voltage limit.

Also, the signal input on pins 5, if thats floating all led's light up, is that how it should be?
 
Pffffft, I can never figure out how to make the proper divider using the pins shown in the data sheets, I just use a divider at the hi and low pins to set the voltage range and use a single resistor to set current. Unfortunately I have little experience cascading these chips.

And yea, don't let the input float, I tend to also use dividers at that pin so even with no signal the pin has a defined voltage.

And it's the voltage drop across the chip drivers that affect wattage...not the drop across the LEDs. (current * voltage * number of LEDs lit. = chip wattage minus the chips overhead)
 

borg123

Joined Sep 20, 2018
1
Think i'm figuring this out,

I used this schematic from sparkfun...

Works beautifully with the input fed via the resistor and capacitor as shown in olpharts circuit, played with the resistor value and got a nice sequence speed for the 500ms on time of a vehicles flasher relay.

i'm going to have a go at running 3 LM3914's now,

i'm wondering about led current, set up like shown above, the led's get just over 7Ma, if i keep the whole circuit running on 5 volts to reduce the volt dropped across the led's (i'll use a buck regulator to drop the 12-16 volts from the car to power the circuit at 5 volts) could i run them at 20Ma without frying the LM3914's?

I could drop the circuit voltage a bit more if it helps?

Hi gazz!

Did you get this working on your car?
Which car do you have?
I have Audi A4 B8.5 (FL), 2014 and it also has 2 tail lights on each side.
From all solutions and circuits I found until now, this seems to be the most possible to use for what I need.
From what I see, I would need to pull only one wire from inner light to outer, am I right?
Thanks!
 
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