# Best practices using 555/4017 & many LEDs

by Freddythunder
Tags: leds, practices
HW Helper
P: 4,540
 Quote by Freddythunder Without going back into the thread, I think you said 6 blues, but each segment is 10 no matter the color. Will this 2 547s be enough for 10 blues? I hope so because I ordered 50. Although that was only $5. It's the level of current that is the important factor. If you increase that series resistor then you can use more parallel strings of two blues, although reducing their brightness in the process. At one stage you said they were too bright for the camera, so this is okay. (I tried to get you to determine the lowest satisfactory current for the blues, but you still haven't.) Are you using 5 parallel strings of two blues each with a 390Ω series resistor? You should increase that to 470Ω to avoid tempting fate. For the circuit values I gave, this was how I summarized it: http://physicsforums.com/showpost.ph...9&postcount=40  I may approach that later but I think I'm going to start with a 556 for each 10 LEDs. So you'll use how many 556's? A dozen or more? That will be eye-catching, to say the least! Reminds me of the time late one Christmas Eve when I strolled down to the corner to have a sticky beak at a colourful Christmas tree decoration that seemed to be lighting up the street, only to discover it was the lights on a police car! (No, I hadn't been celebrating ....)  P: 40 Hi! I used that led calculator I mentioned a few times and then upped the resistance a touch. If they are too bright for the camera I can always adjust the camera or fix it in post. Sorry for not getting the lowest current like you asked. I should have but I need to get this project completed! It's driving me nuts! I made the array 4, 4, and 2 with resistors 47, 47, and 330 ohm respectively. Then I have a different array for reds which I tested the yellows in the same configuration; you saw that video. Here's the blues: http://www.youtube.com/watch?v=jUB2m0NO9Uo New issue. I made the actual circuit board and the timer is working, but the transistors are not. Is there a pretty good chance of getting bum transistors? I've Quadruple checked everything even looked at voltage readings and it just seems the second transistor is dead. Could I have killed it with the soldering iron? It was a terrible pain in the butt soldering on those pad per perf boards. I'm going to get a quote for printed boards and see if I can afford it. I'm planning on using a 556 for each segment of lights. I'll have 8 to start in the overheads which I found a 4' by 10" clear fluorescent light fixture lens that will work absolutely perfectly and will probably spread out the light more too. As time progresses I'll have a few more chunks of LEDs on the pushbar and back window and I can use this same circuit over and over! I've added a 500k ohm trimmer on the first 555 so I can adjust the on off rate per segment. And you were celebrating! Sticky beak is wine! Blue lights are still going! Even my wife likes it!! She said she's proud of me :)  P: 40 Hey I really still appreciate the help. I don't think I would have made it this far without help! Btw HW Helper P: 4,540  Quote by Freddythunder I made the array 4, 4, and 2 with resistors 47, 47, and 330 ohm respectively. You put 4 blues in series? Using 12 volts? I'm surprised you got them to light, though it means you have almost no control over the current in them. I didn't want to have even 3 in series, because the constraints are so tight when using those small signal transistors for the switching. The blues have a higher voltage across them, and 47Ω gives next to no control over the current. Excessive current is likely to damage the LEDs.  New issue. I made the actual circuit board and the timer is working, but the transistors are not. Is there a pretty good chance of getting bum transistors? I've Quadruple checked everything even looked at voltage readings and it just seems the second transistor is dead. Could I have killed it with the soldering iron? No, not with the soldering iron. You most likely killed it with far too much current. Good job it was destroyed now, otherwise it would have happened at a more inconvenient time, e.g., when you are running it off the car's electrical system. Failure is inevitable when you overload that small transistor by making haphazard changes. If you hope to have reliable operation, you have to follow a calculated design. Since you are driving the LEDs with the high current 555, we don't now need to be so frugal with drive current as when using a low output current 4017. I'll take another look at operating 10 blues using one pair of transistors.  Blue lights are still going! Even my wife likes it!! She said she's proud of me :) I'm confused. You say the transistor isn't switching, yet you say the LEDs are still flashing? I'll take a look at some changes to allow 10 blues.  HW Helper P: 4,540 To operate 10 blue LEDs, I suggest that you refer back to the schematic here and make the following changes: change R1 to 2.7kΩ change R2 to 47kΩ and operate 3 strings of 3 blue LEDs in series with 220Ω ½W in parallel with a single blue LED in series with 560Ω ½W If the 560Ω gets noticably warm, replace it with a 560Ω 1W (or, equivalently, a 220Ω ½W in series with a 330Ω ½W). Fingers crossed! P: 40  Quote by NascentOxygen you have to follow a calculated design. I thought I did by following the calculator...  Quote by NascentOxygen I'm confused. You say the transistor isn't switching, yet you say the LEDs are still flashing? Sorry for the confusion; I have two identical circuits, one on the breadboard that was running the blue LEDs, and the one on the little circuit board that had never lit up anything. I ran a single LED to the 556 to check it's operation and it was working, but nothing was going through the transistors. So I don't think I burnt it out. I will try the new resistor values you suggest. Thanks.  HW Helper P: 4,540 Here's an idea if you get printed circuit boards made. Lay it out so each board supports 1x 556, 2x pairs of transistors, and 10x LEDs. When soldering on the blue LEDs, you have one pair of transistors driving 6 LEDs and the other pair driving 4 LEDs. When soldering on yellow or red LEDs, use a few jumper links to drive all 10 LEDs from one pair of transistors, leaving the space for the second pair of transistors empty. HW Helper P: 4,540  Quote by Freddythunder I ran a single LED to the 556 to check it's operation and it was working, but nothing was going through the transistors. So I don't think I burnt it out. I will try the new resistor values you suggest. Thanks. Small signal transistors do get killed without much effort. It is easy to get their leads mixed up. Check that; otherwise, replace it and see whether the circuit starts working.  HW Helper P: 4,540 I'll add a note for when you run your circuit off the car's electrical system... Refer back to the circuit schematic, you'll see capacitor C1. It's there as representative of an attempt to filter potentially destructive spikes that may damage your semiconductors. I suggest that you make C1 using 3 capacitors in parallel to make it closer to ideal: 470uF, 10uF, 0.1uF all in parallel, rated at least 25VW. If I were building this for myself, I'd use a more thorough filter than this, but as you are working to a tight budget, try those and hope for the best. Good luck with it.  P: 40 ...And then 4 months later... Hey Nascent, what does putting the caps in parallel do? I've never heard of that, just the difference between putting resistors in parallel vs series changing the overall resistance - does putting caps in parallel do anything besides offer a different capacitance? I have also seen some sort of regulators that put 4 diodes in a circle.. Do you have another idea to clean up the car power. As this project seems to be taking me years to accomplish, maybe I can build a power circuit next July or so.... In other news, I'm learning that soldering is not my strong suit and I get really frustrated doing it! I've posted asking where I could find some hobbiest to do it for me and see the cost to frustration ratio. Any ideas? HW Helper P: 4,540  Quote by Freddythunder ...And then 4 months later... Hey Nascent, what does putting the caps in parallel do? Welcome back. Again. My suggestion for different capacitors in parallel is an attempt to produce behaviour closer to the ideal. While big capacitors (electrolytics) store a lot of charge, they are slow to react, and fast spikes can still get past them. Smaller capacitors are faster to react, so can better absorb fast spikes, but they can't absorb much energy. Placing a few different ones in parallel is a way to get a large capacitance which can still react fast. I suggested that as a crude protection against transients on the vehicle power supply when the engine is running. If you power the display only while the engine is off, and is kept off, there should be no spikes in voltage. There are regulator ICs available, or something could be constructed using a couple of transistors, but the circuit you built is probably sufficiently robust that the capacitors will do.  In other news, I'm learning that soldering is not my strong suit and I get really frustrated doing it! I've posted asking where I could find some hobbiest to do it for me and see the cost to frustration ratio. Any ideas? Sorry, I have no suggestions. But if you got those printed circuit boards constructed, the soldering should be as straightforward as possible. When soldering, the surfaces must first be cleaned of oxide, and the soldering iron constantly wiped on wet paper to wipe off the lead oxide. They say practice makes perfect, though in the case of soldering, it should read "Lots of practice ....". Good luck!  P: 40 It's been a year and a half. Sheesh.. So printed circuit boards are too expensive. I pulled out all of my stuff determined to finish it so I can move on with the script. I even have a proposed camera man who's brother has a old police car to use. I have six segments constructed and attached to circuits as we have explained. One didn't work. I finally got that one to work and another segment stopped. Along with my patience. :( Sooo, sometime earlier in the year I was thinking it would be so much easier to just have two 556 circuits, which are working great, the ones that work, and have one drive 40 red, the other drive 40 blue. All the segments have resistors attached so I just need power sent to them. In either case I know that if I run numerous transistors off one 556, I'll blow up the 556. I also have an aurdrino I'm contemplating using to drive it. Can I use a power transistor to drive 40 LEDS at once? I tried reading this http://www.sqlskills.com/blogs/pauls...resistors.aspx But left een more confused. I know I can only pull so much and can figure how mush current to push... I think. Can you help a guy one more time :)  HW Helper P: 4,540 Disappointed to learn there has been no progress with this. I shall review the thread to see where things stand.  P: 512 Hello Freddy T.... As a different angle - have you asked any of the companies that make these for a "scratch and dent" - or warranty return that is not sale-able? This is for some type of a movie, if I reacall ( I did read through all 4 pages but remeber this thread) - you can offer to put thank you credits in the scroll.  P: 165 It would be cheaper to buy a lightbar from ebay. I started some projects myself in the last couple of years, and after buying all parts, finding out I didn't have the tools I needed, finding out I would do better with other components than the ones I ordered and re-ordering, finding a box for the stuff to fit in, trying to form the box to work the way I want... etc..... I ended up spending more than I could have spent buying a used unit. P: 40  Quote by NascentOxygen Disappointed to learn there has been no progress with this. I shall review the thread to see where things stand. Ouch. Well I did have six segments blinking the way I wanted and the entire shell constructed. I only get about a day a month to work on this with job and fam. But now I'm ready to get this thing finished!! As for scratch and dent I could ask but imnpretty sure it'd be more. I found one one Craigslist for 250 without a controller. That's the best I've seen. I'm only about$100 down. If I can find a way to send power to the segments and control it with my arduino, then I'm set and it will be better than the 555s anyhow. I got the arduino for free so there'd be much less to buy.
 HW Helper P: 4,540 Just remind me what you have constructed. I think you have multiple boards each something along the lines of this subcircuit: http://www.physicsforums.com/attachm...0&d=1344865437 How many LEDS and what resistor values are you using? They will be different for the blues (the arrangements for reds are identical with those for yellow).
 P: 40 Hello again, Here is a picture I put together with the values of the resistors and how I put the LEDs together. I'm not exactly sure where in the past four pages I got these diagrams, it's not exact to the post you posted. That was more for the transistor setup I believe. After looking at the programming for the arduino and the lack of time I have on just this small piece of the larger project puzzle.... I definitely want to change my mind and use the arduino as the processor. The outputs of the arduino are either high or low. So I can program it to toggle hi and low, then shut off for a while. Due to time restraints, I would love to have two of these outputs - connect one to all 40 reds, and the other to all 40 blues. I figure I can use some solid state method using larger transistors, and tried to research but didn't find anything. I know there are relays, but am afraid they might not be fast enough - but desperate times... thanks again for your help - I'm soooo close!!!

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