RFI on project modification

Discussion in 'The Projects Forum' started by Thoms_S, Aug 23, 2014.

  1. Thoms_S

    Thread Starter New Member

    Aug 23, 2014
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    Greetings.
    I've been looking for a LED SEQUENCER and found a project on this site here: http://www.allaboutcircuits.com/vol_6/chpt_7/6.html. Thank you for posting this BTW. So I've had some fun and built the unit and now I would like to know if there is a way to make this same project with "variable speed"? I put the LEDs in a circle, so it looks like a little radar blip going round and round, but I would like to make it go slower or faster by turning a dial.

    I'm new here and did a quick search for "Variable Speed LED Sequencer" and nothing came up. Apologies if it is some where on site but "wow", this place is big!

    Thanks and love the site.
    TS
     
  2. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    From the site: "Feel free to experiment with resistor and capacitor values on the 555 timer to create different flash rates. "

    So, replace the resistor with a potentiometer (pot), probably use linear one, don't use logarithmic one because log pots are for audio.
     
  3. DickCappels

    Moderator

    Aug 21, 2008
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    ...but put a 1k resistor in series with the pot so the NE555 won't get fried when the adjustment is at the "fast" end of the range.
     
  4. Thoms_S

    Thread Starter New Member

    Aug 23, 2014
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    Sorry that I have not gotten back in so long, I travel a bunch. Here is my update:
    I'm building the LED SEQUENCER from 'allaboutcircuits.com/vol_6/chpt_7/6.html' on a proto-board. I did not get to put the POT in for speed control, I still want to do this but for know I built the original design. I have swapped out the 10-LED-bar to individual LEDs, placed in a circle. Something strange is happening, I turn power (3.5VDC) on and light one comes on and it stalls. But when I place a finger "close - not touching" to the solder side of the 4017 it starts to sequence. (1) Any ideas why and (2) how can I fix it so it runs/stops correctly with just the switch? You can see what I am talking about here: 'youtube.com/watch?v=SK6nv9FU4W8&list=UUQpbzUWkmIYo0eJHuDwp7lw'
     
  5. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Here I have put the pot in the schematic for speed control:

    [​IMG]
    Also put a 10 uF and a 0.1 uF capacitors accross the powerlines of the 555.

    Bertus
     
  6. Thoms_S

    Thread Starter New Member

    Aug 23, 2014
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    Thanks! I appreciate you drawing this out for me. Should the 10uF Cap. go above the 1M pot. in the drawing? Also any idea why the unit stalls and starts? Thank you again so very much.
    Tom
     
  7. bertus

    Administrator

    Apr 5, 2008
    15,650
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    Hello,

    This is said by SgtWookie:

    This can be found in this thread:
    http://forum.allaboutcircuits.com/threads/decoupling-or-bypass-capacitors-why.45583/

    Bertus
     
  8. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    Sounds like the 4017 has a floating input. All CMOS inputs must be tied to a signal, or to V+ or Gnd as appropriate.
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    The 4017 also needs a 0.1uF/100nF bypass capacitor across its' Vdd and GND terminals.
    PROPER SUPPLY BYPASS CAPACITORS ARE NOT OPTIONAL.
    I don't know WHY I have to keep bringing this up, it's a sticky thread in the General Electronics Chat forum. :rolleyes:

    TI's datasheet for the LM555 is here: http://www.ti.com/lit/ds/symlink/lm555.pdf
    Note on the top of Page 3 that the voltage range is 4.5v minimum to 16v.
    You say you are trying to operate it on 3.5v, which is a full volt below the minimum required voltage.
    Consider using a TLC555 instead, the C version can operate as low as 3v, the I version as low as 2v.
    Radio Shack even carries the TLC555C, which would operate with your power supply.
     
  10. Thoms_S

    Thread Starter New Member

    Aug 23, 2014
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    Sorry if I missed something or did not follow protocol here, I'm new at all of this. I just needed the sequencer for a toy I'm building for my daughter, I call it a ''Do Nothing Box''. She can flip the switches and watch the lights run, that's all I'm doing - making a toy. I don't really know all of this stuff. I don't even know what a ''bypass capacitor'' is. I missed the "6v" requirement on the page {allaboutcircuits.com/vol_6/chpt_7/6.html} - guilty, but I thought that would be too much for the LED lamps based on the product description where I bought them: ''Forward Voltages are Clear Red, Orange and Yellow 1.9-2.0V, Clear Green: 2.9-3.1V, Clear Blue, White, Pink and Violet: 3.0-3.2V'' I am using a LM2596 DC-DC converter to control the voltage to the LED lamps. My input is 9VDC and now my output to the LEDs is 4.75VDC, if I go higher some of the other LEDs in the sequencer start to glow a little bit. My apologies if I broke the rules here or did not do some required reading before I posted.
    T.
     
  11. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    In summary, in addition to the timing capacitor in the 555 circuit, it will need 0.1µf and 10µf capacitors between Vcc and Gnd in the 555 chip. Capacitors will also be needed for the 4017 chip. Use 0.1µf in parallel with a 100nf capacitors for the 4017.
     
  12. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    I apologize for being short-tempered, but if you had to continually repeat the same thing over and over again for years, you might begin to understand where I'm coming from. It's one of the reasons that I don't post much anymore, as my available time is rather limited.

    Please read the bypass capacitor thread in the General Electronics Discussion forum, as it will save me a lot of typing.

    One of the big things you need to understand is manufacturer's datasheets; they describe the operating conditions for the component(s) they document, and you need to satisfy all of the requirements in the datasheet for the component(s) in question if you want the circuit to work. It will be a LOT of work at first to try to understand the datasheets.

    The 470 Ohm resistors limit the maximum current through the LEDs. Basically, you subtract the forward voltage from the Vcc, and then divide that by the resistor value.
    For example, your red orange and yellow LEDs have a Vf of 1.9v to 2.0v. Let's assume 1.9v for now.
    6v - 1.9v = 4.1v
    4.1v / 470 Ohms ~= 0.0087 Amperes, or ~8.7 milliamperes (mA). This should be within the maximum current limit of the LED.

    All of your other LEDs have higher Vf's, so the current through them would be less, given the same supply voltage and same resistor value.

    There should only be 1 LED on at a time. If you have more than one on at a time, check for wiring problems.
     
  13. Thoms_S

    Thread Starter New Member

    Aug 23, 2014
    6
    0
    .
    Thank you, I'll add the additional capacitors and see what happens.
     
  14. Thoms_S

    Thread Starter New Member

    Aug 23, 2014
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    As demonstrated by my attaching the original drawing, and stating where and what I was working on by including the URL in every post {{again, the page is here: ''http://www.allaboutcircuits.com/vol_6/chpt_7/6.html''}} the drawing only has one 0.1uF capacitor and the parts list only wants one capacitor so that is the way I built it. Maybe that drawing and www page should be changed? In closing, so sorry to bother you. You won't be bothered again. I did not expect to get flamed on a web site that I thought was to help people. Especially when I followed the instructions for a build posted on that site. I'm gone.
     
  15. MrChips

    Moderator

    Oct 2, 2009
    12,452
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    Welcome to AAC, the best of its kind on the Internet.

    I don't see where anyone has flamed you.

    There are hundreds of tips and tricks to learn in electronics and you cannot possibly learn them all in one project. If you want to expand your knowledge in electronics do stick around. Otherwise, it's your loss.
     
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