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LED Brake Lights (nOOb Question)

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cypher--x

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I want to add some LED brake lights to my street bike but I want them to do more then just turn off and on when power is applied.

I am very very new to electronics and have only done a few minor projects.

Here’s one:
YouTube - Rear peg LED turnlights

Since I am new to this I am trying get more advanced each time. What I want is to wire 9 LED's into the 9V brake light power line. I want all 9 LED's to light when brake is activated and the part I cannot figure out is I want them to turn off when the brake is released in a cascading sequence. I am not sure how to even look this up or what is needed to do this.

Example:

LED: 1 2 3 4 5 6 7 8 9

I want it to turn off in this order:

1 & 9 then 2 & 8 then 3 & 7 then 4 & 6 then 5

I am not sure how to even start this. I thought it could be done with some capacitors but not really sure if I need some kind of timer or what is the best way to do this.

Can anyone help?? Provide a schematic?? Point me in the right direction??
 
An LM3914 is an LED voltmeter IC. It can drive two LEDs in series at each of its up to 10 outputs.

Charge a capacitor quickly at the input of the LM3914 then all the LEDs light quickly. Then discharge the capacitor through a resistor slowly and the LEDs turn off in a cascading manner.
Its max current is 30mA which might not be bright enough for your bike.
 
Car brake lights pull about 2A and parking lights about 1/2A so your LEDs would need about 24/4 = 6w for the brake light and ~2w for the parking lights.
 
An LM3914 is an LED voltmeter IC. It can drive two LEDs in series at each of its up to 10 outputs.

Charge a capacitor quickly at the input of the LM3914 then all the LEDs light quickly. Then discharge the capacitor through a resistor slowly and the LEDs turn off in a cascading manner.
Its max current is 30mA which might not be bright enough for your bike.

Wow!! thx for the quick response but it seems this may be beyond my understanding at this time. I get the idea but no idea how to connect any of this up. What you said went over my head! I'll keep searching around to see if i can figure this out. Any way you could post a circuit diagram of how to connect all this? Looking at the LM3914 datasheet it looks like I may have to make this with 2 Lm3914 and make 1-4 and 6-9 sperate segments

Sorry for the ignorance here!
 
LEDs #1 and #9 are connected in series and are driven from the number 4 output of the LM3914.
LEDs #2 and #8 are connected in series and are driven from the number 3 output of the LM3914.
LEDs #3 and #7 are connected in series and are driven from the number 2 output of the LM3914.
LEDs #4 and #6 are connected in series and are driven from the number 1 output of the LM3914.

The single LM3914 is wired for a BAR display.
With a DC voltage at the input of the LM3914 then all LEDs light quickly. When the DC is removed then a capacitor on the input discharges slowly and the LEDs turn off in a cascaded manner.

We are not a free design service for NOOBs. We talk about how circuits work and how to make them perform better.
 
We are not a free design service for NOOBs. We talk about how circuits work and how to make them perform better.

My apologies, I meant no disrespect and I was not looking for a free handout. Much of this goes beyond my current skill level and I am better at reverse-engineering things then engineering them. I just hoped to see what I needed to better understand HOW it works.

Thank you for the help you provided it has given me a good starting point. I feel I have much to learn!
 
Will this work provided I can calculate the correct resistor values? I am working on this in a very slow manner and want to make sure i am on the right track.
 

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An LM3914 is an LED voltmeter IC. It can drive two LEDs in series at each of its up to 10 outputs.

Charge a capacitor quickly at the input of the LM3914 then all the LEDs light quickly. Then discharge the capacitor through a resistor slowly and the LEDs turn off in a cascading manner.
Its max current is 30mA which might not be bright enough for your bike.

very nice solution, seems very elegant, just a shame about not using the IC to its potential (unused pins)

could a similar idea work, but using the output from the capacitor to saturate the bases of transistors at different levels, therefore eliminating the need for an IC totally?
 
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Okay since it seems the LM3914 set up will not provide enough power to run the LED's in series like I want, I went back to basics (well I very new so really I never left basic)

Perhaps this would work. It may not be the cleanest solution but if I used different size caps with the LED's in groups wouldn't the caps discharge at different rates creating a cascading sequence? The value of the caps may not be correct in my diagram but you get the idea. It may require larger variation between each cap.

Or am I going to blow myself up?
 

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The LM3914 can drive up to three red LEDs in series on each output when it has a 9V supply. It can be set to provide a regulated current up to 30mA on each output which is plenty for ordinary LEDs. Its regulated output current does not need current-limiting resistors.

Your circuit with the capacitors would just blink the LEDs for a moment.

The LM3914 can have the 1st LED in series with the 10th LED and they would light and stay lighted, then the 2nd and 9th LEDs would light and stay lighted, then ther 3rd and 8th LEDs would light and stay lighted, then the 4th and 7th ....., exactly what you want.

Or the LM3914 can light up to 10 LEDs or up to 30 LEDs (in series) in sequence.
 
I have been playing with the LM3914 on my breadboard and I can not get it to work. I am not giving up on it but I think it may be more complicated then i can understand at this time.

I started with trying to build the "Typical Application" to understad how it works. then i was going to move on to the second application. Then eventually to your suggested application but i cannot even get the first one to work. The datasheet i found for the LM3914 helped me understand how it works a great deal and i understand how your suggestion will function but i still can't even the "Typical Application" to work.

The LED's I'm using have these spec:

Emitted Colour : Yellow
Size (mm) : 3mm
Lens Colour : Water Clear
Peak Wave Length (nm) : 585 ~ 595
Forward Voltage (V) : 1.8 ~ 2.2
Reverse Current (uA) : <= 30
Luminous Intensity Typ Iv (mcd) : 4000(Typical) ~ 5000(Max)
Life Rating : 100,000 Hours
Viewing Angle : 20 Degree
 

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Your LEDs with capacitors will just blink the LEDs for a moment.
Make the LM3914 circuit like this:
 

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What is the forward current [If] at the Vf of 2V?
You have a graph of Vf vs. If for these LEDs?
Most ordinary little LEDs have a max continuous current of 30ma. Their brightness and voltage are rated at 20mA.
The forward voltage is a range from 1.8V to 2.2V and a graph won't show the range.
The forward voltage graph of a low voltage LED like this is almost a vertical line.

These LEDs have a very narrow 20 degrees beam width.
 
Your LEDs with capacitors will just blink the LEDs for a moment.
Make the LM3914 circuit like this:

Thank you for posting this I will build it up again tonight and see if I can get it to work this time.

Not to look a gift horse in the mouth and ask for more but will this work with only five sets of LED's (10 total)? At what range cap and resistor should I start with for C1 and R1? I connected it up last night with a 2.2 uF cap and a 3.8k ¼W resistor and just got a puff of smoke from the resistor. Figured it was because it was only a ¼W. What would be a good start point?
 
Not to look a gift horse in the mouth and ask for more but will this work with only five sets of LED's (10 total)?
Then the 1.8k resistor will need to be re-calculated so that the 5th output is active (instead of the 10th) when the input voltage reaches 7V. Change the 1.8k resistor to 3.9k.

At what range cap and resistor should I start with for C1 and R1? I connected it up last night with a 2.2 uF cap and a 3.8k ¼W resistor and just got a puff of smoke from the resistor. Figured it was because it was only a ¼W. What would be a good start point?
When the input is 9V then the 3.8k (not a standard value) resistor has 8.3V across it. The power in the resistor is (8.3V squared)/3800= 0.018W which is nothing. The resistor will not even feel warm.

The time for the LEDs to nearly turn off is R x C. Using 100k and 100uF will result in a time of 10 seconds.
 
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