## Best practices using 555/4017 & many LEDs

Hello,

I'm new here.. I have a question about running a lot of LEDs in a couple scenarios. I'm building a full-size lightbar for a fake police car to be used in movies. I found a schematic for the red & blue LEDs that I'm going to duplicate using some 555s or 556 here:
http://www.instructables.com/id/41-L...-using-555-IC/

But I would also like to (easily & cheaply on a no-production-value film budget) get yellow LEDs on the back that would show direction by illuminating at one end and moving across. I've made this before using a 555 and a 4017, but only one LED at a time. I want to make it realistic so I'm dropping about $80 in LEDs so each segment would be 6-10 (30mA) LEDs instead of just one little one. What would be the best, cheapest and most reliable way to do this? Can I use a transistor for the added current or a relay of some sort? I've been searching on and off for months for this solution, but I don't think I know the proper nomenclature to find what I am looking for. Thanks!  PhysOrg.com engineering news on PhysOrg.com >> PNNL-developed injection molding process recognized with emerging technologies award>> How soon could car seats enter the 3-D comfort zone?>> NASA: Austin, calling Austin. 3-D pizzas to go  Recognitions: Gold Member Both transistor or the relay will do. If you use relays, then you would need to freewheeling diodes to prevent from inductive over-voltage. Or you could use transistors just as well. Make sure the transistor can provide the current required, and you bias the base with appropriate current. I think using transistors would be cheaper and more reliable . And, welcome to PF.  You probably don't want to switch relays as fast as your application will want. In addition the power supply requirements are much higher for driving relays as opposed to driving transistors. Go with the transistors. ## Best practices using 555/4017 & many LEDs Awesome, transistors it will be. Thanks for the help. I think that opened a lot of doors. This whole time I had never googled "transistor as a relay" (duh) and got a bazillion results. I'm going to read a few thousand of those and then I'll come back if I have any questions. Thanks!  Actually, hang on, I have another question. I ran across this before about a year ago: http://wild-bohemian.com/electronics/flasher.html I remember that transistor configuration to make LEDs blink. I actually tried to get my dad to look at it (actually went to school for this stuff... I didn't) and he never got back to me. Since the LEDs are on the positive side of the transistors, is it feasible for me to run an array of LEDs off of this or will I blow up the transistors because the current still needs to course through them. This is for a car so I'll have tons of current at 12-14 volts. ...Or should I stick to the 555/6 flashers and make arrays through transistors? Thanks again! I'm very happy I found someone[s] who can help me with this stuff! Recognitions: Homework Help  Quote by Freddythunder But I would also like to (easily & cheaply on a no-production-value film budget) get yellow LEDs on the back that would show direction by illuminating at one end and moving across. I've made this before using a 555 and a 4017, but only one LED at a time. I want to make it realistic so I'm dropping about$80 in LEDs so each segment would be 6-10 (30mA) LEDs instead of just one little one.
How many segments will comprise the full arrow? Each segment being made up of 6-10 LEDS one above the other in a vertical line?

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 Quote by Freddythunder 'm building a full-size lightbar for a fake police car to be used in movies. I found a schematic for the red & blue LEDs that I'm going to duplicate using some 555s or 556 here: http://www.instructables.com/id/41-L...-using-555-IC/
How many LEDs do you plan to combine for the blue light? That circuit as it stands can probably power at least double the number shown when you operate it off 12 volts, so maybe 40-50 blue LEDs. Much the same for the red.
 I really want to do this right and have it look as non-cheesy as I can, so I'm actually upping the amount of LEDs from what I said before and doing it right. So, I'd like to have 80 red on one side, 80 blue on the other. If I could use a power transistor or some kind of configuration for this circuit: http://www.555-timer-circuits.com/police-lights.html (noted the wrong one before - sorry!!) The yellow ones in the back would be 10 segments of 20 LEDs each segment. I have put together an online model to explain in full detail what I would like to create. To activate it, click the grey buttons labeled "code3" and "yellow" http://www.freddythunder.com/film/lightbar.html Then once all that is done, if I want the yellow lights to blink like the red/blue ones, I'll just duplicate that circuit. I'm thinking that each section of LEDs will be a module with wires coming off of it and I can build a "brain" into one circuit board to control everything with a few 555/4017 combos. Whaduyathink?
 Recognitions: Homework Help In that circuit, they are supplying one of the colours with ten times the current as the other. I haven´t played the video, does it tell you which of their LEDs needs the greater current? On your animation, I think you have the blue flashing differently to the red. In any case, it is too fast for me to figure out: are you wanting to flash any blue simultaneously with any red? Maybe you could slow it down to one quarter actual speed?
 No I'm not sure why any of them would need 10 times the current. I'm too much a noob. On the animation, the way I'm thinking, there's 2 blue and 2 red sections that fire and blink and then shut off, then it alternates to the remaining 2 blue and 2 red sections. The 555 sends a box wave (right?) to the 4017 making it alternate which 'side' fires. I'm sure I can get the circuit to work like the video shows, but my only question is can I use a bigger transistor and run 80 LEDs on each side of that circuit, or do I have to make multiple circuits. As for the speed & the way they blink, quite frankly, I don't care. Just as long as they blink. It's just special lighting for the movies ;) Thanks for your help
 Recognitions: Homework Help A pair of transistors should be able to drive 40 LEDs, at least. But first we need to know the voltage and operating current of your LEDs, an this will differ for red and blue. Have you chosen the LEDs? There are basically two choices: standard LEDs and high brightness LEDs, the latter costing more and using more current. Different coloured LEDs differ in their efficiency at producing light, and the eye has different sensitivities between red and blue, so to have similar apparent brightnesses it can be desirable to power the different coloured LEDs with different currents. The 555 generates a square wave.
 Recognitions: Homework Help A selection of web pages illustrating details to consider, I'm not endorsing any sites. Two pin or four pin LEDs: http://www.superbrightleds.com/cat/c..._Flux,18,1221: Flat-top LEDs for wider viewing angle: http://www.plasmaled.com/bright-led-...-10mm-flat.htm Cheap 100 packs: https://www.sparkfun.com/categories/172
 Thank you for those links! I would have loved to [see if my budget allowed to] get those instead with the larger viewing. I have already bought 110 of the LEDs already from here: http://ledshoppe.com/led10mm.htm The white and blue are: Emitted Colour : WHITE Size (mm) : 10mm Lens Colour : Water Clear Peak Wave Length (nm) : N/A Forward Voltage (V) : 3.2 ~ 3.8 Reverse Current (uA) : <=30 Luminous Intensity Typ Iv (mcd) : Average in 750 00 Life Rating : 100,000 Hours Viewing Angle : ±10° Absolute Maximum Ratings (Ta=25°C) Max Power Dissipation : 80mw Max Continuous Forward Current : 30mA Max Peak Forward Current : 75mA Reverse Voltage : 5~6V Lead Soldering Temperature : 240°C (<5Sec) Operating Temperature Range : -25°C ~ +85°C Preservative Temperature Range : -30°C ~ +100°C and the red/yellow are: Emitted Colour : Red Size (mm) : 10mm Lens Colour : Water Clear Peak Wave Length (nm) : 640 ~ 645 Forward Voltage (V) : 1.8 ~ 2.2 Reverse Current (uA) : <=30 Luminous Intensity Typ Iv (mcd) : Average in 10000 Life Rating : 100,000 Hours Viewing Angle : ±10° Absolute Maximum Ratings (Ta=25°C) Max Power Dissipation : 80mw Max Continuous Forward Current : 30mA Max Peak Forward Current : 75mA Reverse Voltage : 5~6V Lead Soldering Temperature : 240°C (<5Sec) Operating Temperature Range : -25°C ~ +85°C Preservative Temperature Range : -30°C ~ +100°C These LEDs have a very narrow viewing angle, but they are as bright as the sun. I'm thinking with the right blinking speed combined with camera height, shutter speed and aperture settings, I'll get real close enough to one of the new \$500 lightbars on real cop cars - at least on film. Thanks!

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 Quote by Freddythunder The white and blue are: Emitted Colour : WHITE Size (mm) : 10mm Lens Colour : Water Clear Peak Wave Length (nm) : N/A Forward Voltage (V) : 3.2 ~ 3.8 Reverse Current (uA) : <=30 Luminous Intensity Typ Iv (mcd) : Average in 750
Those blues are so dim in comparison with your reds that you may decide to buy brighter blues. Could you power a handful side by side with an equal number of reds, and view them head-on from a distance to see how they'd go? The yellows and reds sound good.

At 10mm, they are big ones. You've bought 100, but on the figures you gave you'll be needing at least 400?

Yes, you could work within viewing angle restrictions by always filming head-on.
 Recognitions: Homework Help Just check your figures on your whites and blues, as that site currently doesn´t list 750 mcd LEDs, certainly not in 10mm. At first glance, I think it will be feasible to use a driver module, and with care operate parallel strings for the blinking LEDs, e.g., the decade counter can control two 4015 modules each driving 84 LEDs to produce the blinking. To keep down cost, the yellow LEDs can be switched by transistors. Have a look at the 4015 BoostPuck here. Without boosting the +12v from the car battery, you´d be limited to powering 3 of the blue LEDs in a string; by boosting it to +28v you can power 7 blue LEDs per string.
 Okay. Sorry for the delay. Got laid off from my job and have been job hunting ever since. I read somewhere on here that I can't count and it seems I cannot. Sorry my led count was off. But it looks like I still have some planning to do. I took a look at a real lightbar a couple days ago and I think the LEDs are ten on top, five on bottom so it may be less LEDs anyway. So what you are suggesting instead of using the bc547 transistors (or alternate higher power transistors) I could use these boost puck thingies? Looks like a new world. And can you show me how I would get the yellow ones to work like that using just transistors? Maybe a link to a tutorial or something? I'm real close to just making the red and blue blink back and forth with just transistors to save time and money. As for the brightness, no matter what the numbers say, both the red and blue are bright enough for filming. They may actually be too bright and I may have to use larger resistors, that is if I ever get that far. Thanks for the help!

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 Quote by Freddythunder Okay. Sorry for the delay. Got laid off from my job and have been job hunting ever since.
Nasty. Not something you saw coming?
 So what you are suggesting instead of using the bc547 transistors (or alternate higher power transistors) I could use these boost puck thingies? Looks like a new world.
I was suggesting this, it would save transistors and resistors and a lot of connections. However, in light of your opinion that at full current the LEDs may be too bright, this eases the design constraints I was working within.

It's tempting to connect 3 of the blue LEDs in series with a resistor and power that string from the +12v. But there's a difficulty in designing for say, 22mA of LED current at a battery voltage of +12, while avoiding having that current soar to almost double that value as the battery warms up under charge and its terminal voltage rises to around +13.5v.

That regulator module I pointed to would have solved this. However, until you work out precisely how many LEDs need to be powered in unison, this can remain as "to be decided".

Regardless, some tests for you: connect one of your blue LEDs in series with a 390Ω resistor to a +12v supply, and record the voltage across the LED. Now substitute one at a time another fifteen blue LEDs, recording their voltage each time. That will indicate the voltage spread to allow for.

Can you do the same for your YELLOWS and, separately, the REDS.

At this stage I'm needing to know how many RED and BLUE together will flash in unison, to see whether they can all be economically powered via a single transistor.

As for the job hunting -