Another LED project. Well it was working

Discussion in 'The Projects Forum' started by chongolio, Jun 28, 2010.

  1. chongolio

    Thread Starter New Member

    Mar 22, 2010
    21
    0
    So I thought I would try out another flashing LED circuit using a 4026 and 555 IC chip while waiting for another 4017 replacement chip for the LED chaser I am having problems with . This was my first attempt using a perfboard. Well the first time I applied power the thing worked! I was quite proud of myself because I figured out the layout of all the components on my own. I played around with a couple different capacitors until I found a blinking rate that I liked. I then installed the circuit in an art piece I am working on. I tested it periodically to make sure I didn't short anything out while making everything fit. So far so good. The next day I installed a power switch and thats when the circuit stopped blinking and would just light some of the LEDs. I did all the usual inspections and re-soldering and also replaced the capacitor but nothing changed. I did however notice that when I switched the power on and off that the LED's being lit would change. I did some experimenting with wiring the power points of the circuit up to one of the output pins of the same timing circuit on a breadboard. I discovered that I could get the circuit's LED to blink somewhat "randomly" again so the project is not a total wash, but I sure wish I knew what had happened to the circuit to make it quit working correctly. Any ideas or suggestions on why this may have happened and how to troubleshoot it?

    Here are the schematics and my circuit layout (a few changes were made on the fly when soldering it up)
     
    Last edited: Jun 28, 2010
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Show us a schematic please. Did the LEDs have drivers, or were they driven directly from the chips, and what was the current to the LEDs?
     
  3. chongolio

    Thread Starter New Member

    Mar 22, 2010
    21
    0
    Schematics now uploaded in my original post. The LEDs went directly to the chip. I never measured the current in the circuit. On my circuit layout picture the LEDs are wired to the green pin numbers and to ground
     
    Last edited: Jun 28, 2010
  4. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    The huge mistake was no resistors. Resistors MUST be included with LEDs, it is not optional. LEDs are current devices, they do not limit current in the slightest. CMOS is the weak link, but if it hadn't blown first the LEDs would have popped. I've written an article covering this in detail (including driving LEDs from CMOS).

    LEDs, 555s, Flashers, and Light Chasers

    I empathize for what its worth. LEDs are fun circuits. My blog, which is included in the above link, covers a lot of circuits like that. I've also written a series of articles for the AAC book using 555's and protoboards, The 555 Projects. This link is the articles before they were released, if you want to access the AAC book look up the experiments, Volume 6, which has a lot of good ideas.
     
  5. chongolio

    Thread Starter New Member

    Mar 22, 2010
    21
    0
    Thanks Bill, I kinda was wondering about the lack of resistors in this circuit. But it was just a passing thought that came and went. So I guess I managed to fry another chip. I am going to go back and reread your article, maybe this next time some of your info will stick
     
  6. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Side note, it might have lasted if the circuit had less voltage. CMOS is funny, it will current limit with low voltage power supplies. As the power supply voltage goes up this current limiting goes up. I would never recommend it, though I've used if for 3V power supplies. For one thing it isn't consistent, one chip may limit at 2ma, while another at 26ma. It is not predictable enough to use reliably.
     
  7. chongolio

    Thread Starter New Member

    Mar 22, 2010
    21
    0
    I went back and replaced the 555 chip and added 330 ohm resistors to each LED. The circuit is working again and blinking, However p-13 will not blink it just stays lit. I can live that and gonna guess the 4026 IC might have took a hit also when the current was running wild.

    Thanks again for you help Bill
     
  8. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Your circuit needs a very important supply bypass capacitor to keep the 9V from jumping all over the place when the output of the 555 switches and draws 400mA for a moment which will kill the 9V and then the 555 and counter get confused. Use 1uF to 47uF depending on the frequency. The datasheet for the LM555 recommends two supply bypass capacitors in parallel. Add a 0.1uF ceramic disc capacitor close to the supply pins of the 555.
     
  9. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    He's right, I've seen something similar. A fresh battery doesn't have this problem, but as they get weaker it crops up.
     
  10. chongolio

    Thread Starter New Member

    Mar 22, 2010
    21
    0
    Ouch I just put the whole project back together because everything was working fine. With the new battery all the light were even blinking. I guess I better be prepared for the circuit to go haywire again. That schematic I found obviously wasn't put together by somebody who knew what they were doing :(
     
  11. chongolio

    Thread Starter New Member

    Mar 22, 2010
    21
    0
    I found the page where I got the schematics if anyone is interested. The guy give his reasons for not having the suggested resistors and capacitors. What I failed to notice is that he recommends using a lower voltage than the listed 9 volts.

    Here is the page url:
    http://www.instructables.com/id/Fireflies---Analog-version.../

    So far the circuit has been working fine using the 9v
     
  12. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    You gotta have resistors for LEDs, especially for higher voltages. Many projects get by with it by using gimmicks like low voltage batteries with high internal resistances to replace real resistors. In this case it appears he is using the CMOS characteristic I mentioned earlier.

    There is nothing wrong IMO with going beyond the limits of components as long as you understand what and why your doing it, and no one is at real risk if it fails (think traffic lights for example). Its all part of the fun.
     
  13. chongolio

    Thread Starter New Member

    Mar 22, 2010
    21
    0
    This circuit has been working with out any problem for several weeks now even as the battery has run it's course the only thing noticable is the dimmer LEDs and a bit of a flicker. I am gonna venture a guess that powering the circuit from a wall wart might of caused some of my earlier problems
     
  14. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
    The 4026 is a seven segment decoder. Pin 13 is the c segment which is lit during 0,1,3,5,6,7,8,9 ... that is why it always appears to be on. Another thing is your 555 frequency is approximately 14 Hz or 14 times per second. If you want the c-segment to flash you'll have to slow that down. At 1 Hz, c-segment will still be lit except for 2 and 4 or twiceevery 10 seconds.
     
    Last edited: Jul 22, 2010
Loading...