# A learning project

#### Printz

Joined Oct 2, 2010
31
Well I tried this once before and because I didn't read the rules thoroughly it got closed. So let me try this again. I want to build a circuit that does this http://www.youtube.com/watch?v=eqId7g7SC10&feature=related but when one lights up it stays lit. There are other functions I want to add later too, but lets see if I can handle this first.

#### Printz

Joined Oct 2, 2010
31
The video is just a 7490 decade counter being driven:

However as far as them staying lit up to make a sequential deal, then all cycling of and starting over again you'd go about it a different way. Just woke up from a nap so I can't think of anything at the moment.
Could I use 2 of them in sequence to run 8 rows of 4 LED's? This might work fine, the input voltage is already pulsed.

#### marshallf3

Joined Jul 26, 2010
2,358
Could I use 2 of them in sequence to run 8 rows of 4 LED's? This might work fine, the input voltage is already pulsed.
If I recall they actually come with 10 outputs insequence but I don't think they have very high output capabilities at all thus requiring driver transistors for each output leg.

#### Printz

Joined Oct 2, 2010
31
Each output won't have to drive but 4 LED's. Still to much?

#### KMoffett

Joined Dec 19, 2007
2,821
The "absolute maximum" sinking output (Iol) is 16mA
http://webpages.ull.es/users/fexposit/7490.pdf
You could place 2 LEDs (Vf=1.7v) and a 127Ω resistor in series, and two of these in parallel for each output, for 4 LEDs per output. But, that doesn't solve the light-and-stay-on condition that you want. I'd use a 555 driving a CD4017 Johnson counter, followed by an OR'ing diode matrix, followed by 4 NPN common-emitter LED drivers. This will give you lots of options for different sequences.

Ken

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#### John P

Joined Oct 14, 2008
1,808
A 74190 wouldn't do what the video shows, and in fact the notes attached to the video explain that the output element is a 74138 demultiplexer. With that, you can get 8 light clusters even though only 4 are shown.

If you use a 74HC138, the maximum output current per pin would be 25mA, though going that high wouldn't be wise. With 4 lights per cluster, you could still get them pretty bright if they're the high-efficiency type.

#### Printz

Joined Oct 2, 2010
31
The "absolute maximum" sinking output (Iol) is 16mA
http://webpages.ull.es/users/fexposit/7490.pdf
You could place 2 LEDs (Vf=1.7v) and a 127Ω resistor in series, and two of these in parallel for each output, for 4 LEDs per output. But, that doesn't solve the light-and-stay-on condition that you want. I'd use a 555 driving a CD4017 Johnson counter, followed by an OR'ing diode matrix, followed by 4 NPN common-emitter LED drivers. This will give you lots of options for different sequences.

Ken
The 555 and 4017 were the way I was leaning to begin with. I wasn't sure it would hold the rows on in sequence.
A 74190 wouldn't do what the video shows, and in fact the notes attached to the video explain that the output element is a 74138 demultiplexer. With that, you can get 8 light clusters even though only 4 are shown.

If you use a 74HC138, the maximum output current per pin would be 25mA, though going that high wouldn't be wise. With 4 lights per cluster, you could still get them pretty bright if they're the high-efficiency type.
I'm trying to control 8 rows of 4 lights, to make two sides. Turning on from the inside to the outside, like blinkers. If I'm going to be programming something, why don't I go ahead and add another function to the array. I just figured wire it differently to do this one but maybe it might be easier to digitize it. I'm trying to get the 2 array's to operate as one to create brake and running light on my bike.... that has a 2 stroke bolted to the frame.

I hope I'm not breaking the no automotive rule, I didn't mean to before so if this still falls under that I'm sorry. It's not required to be plated or registered and I just want to be seen better at night. Thanks again everyone.

#### KMoffett

Joined Dec 19, 2007
2,821
"I'm trying to control 8 rows of 4 lights, to make two sides." With the 4017 just parallel each set of 4-LEDs-and-1-resistor with another set of 4-LEDs-and-1-resistor. One set of each pair will be on the right, the other on the left. You may have to change the 10K resistors to a lower value (4.7K ?) to drive the extra collector current in each transistor.

Is the chaser version the running light or the brake light? Is the other mode to be just steady, no flashing?

Ken

#### beenthere

Joined Apr 20, 2004
15,819
create brake and running light on my bike.... that has a 2 stroke bolted to the frame.
We will let this one go, as the intent is to enhance safety. The OP should use care in construction and mounting, not to mention weatherproofing all connection.

#### marshallf3

Joined Jul 26, 2010
2,358
I've seen those little weedeater engines that can be clamped to a bike frame and run against the wheel, you can often pedal faster.

#### Printz

Joined Oct 2, 2010
31
"I'm trying to control 8 rows of 4 lights, to make two sides." With the 4017 just parallel each set of 4-LEDs-and-1-resistor with another set of 4-LEDs-and-1-resistor. One set of each pair will be on the right, the other on the left. You may have to change the 10K resistors to a lower value (4.7K ?) to drive the extra collector current in each transistor.

Is the chaser version the running light or the brake light? Is the other mode to be just steady, no flashing?

Ken
The steady will be the running light, which gets brighter for the brake. The chaser is the blinker. I had a little doubt that I'd be able to pull this off. My electronics background is only repairing radar units as old as me.
We will let this one go, as the intent is to enhance safety. The OP should use care in construction and mounting, not to mention weatherproofing all connection.
I plan on putting the electronics in a sealed box, heat shrinking the wires so it looks clean too. As a future Mechanical Engineer, that's what I'm studying in school, I will make sure to be careful. Thanks.

Mitchell

#### KMoffett

Joined Dec 19, 2007
2,821
So the chaser is the left/right turn-signal?

Ken

#### Printz

Joined Oct 2, 2010
31
So the chaser is the left/right turn-signal?

Ken

Correct sir. I'll try and draw a picture if it will help, but knowing my art it won't do any good.

#### tom66

Joined May 9, 2009
2,595
Correct sir. I'll try and draw a picture if it will help, but knowing my art it won't do any good.
I think turn signals are not allowed to be sequential in some places.

Wikipedia (http://en.wikipedia.org/wiki/Turn_signal#Turn_signals):

FMVSS 108 has been officially interpreted as requiring all turn signal lights to illuminate simultaneously.[35][48] However, the 2010 Ford Mustang is equipped with sequential turn signals.[49]

However, as it says the Mustang has them so maybe there are some exceptions.

#### Printz

Joined Oct 2, 2010
31
I think turn signals are not allowed to be sequential in some places.

Wikipedia (http://en.wikipedia.org/wiki/Turn_signal#Turn_signals):

However, as it says the Mustang has them so maybe there are some exceptions.
Not to sound like a smart-a but this thing already is a rolling gray area, so adding the signals is the last of my worries. I'm just super excited to have a brake light and BRIGHT tail light. Let me do some searching on the laws and see if we can make the running light pulse slightly for better night visibility. I'll make sure about the turn signal laws too.

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#### wayneh

Joined Sep 9, 2010
16,384
...this thing already is a rolling gray area...
Well put! Scooters are definitely on the fringe, and in some places this actually favors the scooter rider since the police would rather look the other way than try to figure out which laws are being broken or not. Behave yourself and they'll leave you alone.

#### Printz

Joined Oct 2, 2010
31
Well put! Scooters are definitely on the fringe, and in some places this actually favors the scooter rider since the police would rather look the other way than try to figure out which laws are being broken or not. Behave yourself and they'll leave you alone.
It's worked for me so far, they leave the bike alone. Once I get this figured out on the bike I'm going to make another more polished version and try it on my 50cc scooter which they really hate, since it doesn't have or need plates and it'll still do 50mph. Safety is the name of the game right now though. Thanks again guys!

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#### marshallf3

Joined Jul 26, 2010
2,358
However, as it says the Mustang has them so maybe there are some exceptions.
So are the classic Ford Thunderbirds and a few other cars.

It's all about they don't want people to think you're driving a police car.