Connect with us

Help with LED strobe

Discussion in 'LEDs and Optoelectronics' started by peter.s, Dec 18, 2014.

  1. peter.s

    peter.s

    37
    3
    Dec 18, 2014
    Hi there - I've been searching the web for information on how to build an LED strobe (12 volts) and came across this fabulous forum. Another person posted a similar project here a couple of years ago (https://www.electronicspoint.com/threads/12v-led-strobe-controller.254837/), which is helpful but there are a few things which are unclear to me - hopefully someone here can answer a few questions?

    Basically I want to make a wig-wag (strobe 3 times side A/strobe 3 times side B) with very bright white LEDs. A diagram for this was posted on the other thread (see attached), but I'm having a little trouble understanding it…. this may sound stupid, but I can't get my head around all those numbers on the right side of the 4017BP (circled in green). I get the 00, 01, 02, etc. are pin numbers (I think), but what's with the 3, 2, 4, 7, 10, etc.?

    Also, will this set up allow me to use (maybe) 30w of power for the LEDs?

    Any advice welcome - thanks in advance.
     

    Attached Files:

  2. KJ6EAD

    KJ6EAD

    1,114
    157
    Aug 13, 2011
    00, 01, etc. are not the pin numbers. They are the sequential numbers of the outputs. The pin numbers are on the outside of the IC outline.

    For higher powered outputs, use each of the existing transistors to drive the gate of an appropriately sized FET. The IRF610's shown in Kris' pod driver schematic from that same thread should be adequate unless you exceed 30W per channel or operate the FETs in a hot environment.
     
    Last edited: Dec 18, 2014
  3. Arouse1973

    Arouse1973 Adam

    5,164
    1,078
    Dec 18, 2013
    Hello
    It's not 00 it should be Q0 and Q1 etc. It is just the outputs in the order they switch. Why Q you ask, it's tradition that stems back many years and although there are many speculations like it was the shape of the transistor or in case the person typing the data sheet got O mixed up with 0 they made it Q. I think it comes from the word Quelle which means transistor source in German.
    Adam
     
  4. peter.s

    peter.s

    37
    3
    Dec 18, 2014
    Thanks for your responses.

    Just to check I understand - From the IC 4017BP to the 4075BP, pin 3 goes to pin 1 / pin 4 to pin 2 / pin 10 to pin 8... And then pin 9 from 4075BP to R3 (2.2kohm) then to the transistor.... right?

    I don't have these components in front of me but I've just looked them up on google and noticed that the IC 4017BP has 16 pins (one data sheet I looked at suggests pin 16 is for +V). This diagram does not show a pin 16. Any ideas?
     
  5. Arouse1973

    Arouse1973 Adam

    5,164
    1,078
    Dec 18, 2013
    Yep that's what the diagram shows. Oh and don't forget 1-3 6-4 11-5 and 6 to R6 :)
    Adam
     
  6. KJ6EAD

    KJ6EAD

    1,114
    157
    Aug 13, 2011
    I used an old student version of Multisim to draw that schematic which is probably why the Qs weren't shown correctly. Some schematic symbols omit power pins so pin 8 is ground and pin 16 is VCC.

    Since we're nitpicking details of nomenclature now, the traditional method of describing pin to pin connections would be something like this: U2-3_U3-1, U2-4_U3-2, U2-10_U3-8, etc.
     
    Last edited: Dec 18, 2014
  7. peter.s

    peter.s

    37
    3
    Dec 18, 2014
    Yeah :), I just didn't want to bore you by writing it all out... The diagram is written as if there are two 4075BPs, but I'm guessing there is actually one... right?

    Also - is the strobe speed (flash rate?) governed by C1 or C2? or maybe something else?
     
  8. KJ6EAD

    KJ6EAD

    1,114
    157
    Aug 13, 2011
    U3 is one component shown on the schematic as U3A and U3B.

    The clock speed is controlled by R1, R2 and C1 as is typical for a 555 astable.
     
  9. peter.s

    peter.s

    37
    3
    Dec 18, 2014
    Thank you both so much!

    It may be a few days before I put this together and try it out, so I will probably be coming back with more questions some time in the New Year.

    Happy Holidays !!! :)
     
  10. Arouse1973

    Arouse1973 Adam

    5,164
    1,078
    Dec 18, 2013
    And you mate. Good luck
    Adam
     
  11. peter.s

    peter.s

    37
    3
    Dec 18, 2014
    I've bought most of the components for this project, but in studying the list I noticed that R4 and R5 are different values. I would have thought them to be the same... is there a reason for them to be different?

    Also, C1 and C2 are a lot smaller than I expected (see picture), did I get them right?

    Cheers.
     

    Attached Files:

    • C1C2.jpg
      C1C2.jpg
      File size:
      21.8 KB
      Views:
      117
  12. KJ6EAD

    KJ6EAD

    1,114
    157
    Aug 13, 2011
    R4 and R5 differ because the forward voltage of red LEDs are lower than that of blue LEDs. The values are chosen to equalize current. In actual practice, an adjustment will be made "by eye" to match apparent brightness.

    The capacitors don't need to be physically large to have the correct capacitance at a 50V rating.
     
  13. Colin Mitchell

    Colin Mitchell

    1,419
    314
    Aug 31, 2014
    The the transistors are emitter-followers so you don't need the 2k2 resistors.
     
    Last edited: Dec 28, 2014
  14. KJ6EAD

    KJ6EAD

    1,114
    157
    Aug 13, 2011
    They are? I thought that was a common emitter topology. If the load or it's resistor were open, wouldn't the OR gate see high current without the base resistor?
     
    Last edited: Dec 28, 2014
  15. Colin Mitchell

    Colin Mitchell

    1,419
    314
    Aug 31, 2014
    If the load is open the OR gate will see high current through the base. But the load is not open.
    I see what you mean. The collector can only rise to 8v and the 2k2 will take up the difference between the base voltage and the output of the OR gate. The approx 3v across the 2k2 will allow just over 1.3mA base current
     
  16. KJ6EAD

    KJ6EAD

    1,114
    157
    Aug 13, 2011
    It's cheap insurance. Hobbyists and the inexperienced are known to connect and disconnect loads indiscriminately with the circuit powered just like they would with most consumer devices. o_O
     
  17. peter.s

    peter.s

    37
    3
    Dec 18, 2014
    Yep, I'm a novice so cheap insurance sounds good to me :)

    Good thing I asked about R4 & R5. I intend to use White LEDs - so will these resistors be a different value?

    And, when asked about the capacitor voltage at the electronics store I said 12 volts. But "...correct capacitance at a 50V rating." suggests that I made a mistake. Should I be getting capacitors rated for 50v?
     
  18. KJ6EAD

    KJ6EAD

    1,114
    157
    Aug 13, 2011
    You stated earlier that you intend to use high powered LEDs. This circuit can't drive them directly. You must modify the circuit to include the FETs previously mentioned in post 2.

    Any rating above 12V will work for the capacitors. I mentioned 50V because that's the lowest available rating for most ceramic capacitors.
     
  19. peter.s

    peter.s

    37
    3
    Dec 18, 2014
    Yes, so R4 & R5 become obsolete?

    I've just been reviewing the diagram in the other thread mentioned in my first post and I think I have a handle on it. If I run into any more trouble I will be back :)

    You guys are so helpful - Happy New Year !!!
     
  20. peter.s

    peter.s

    37
    3
    Dec 18, 2014
    Hi Kj6ead - I've drawn up a quick diagram of how I think this should be. Could you please take a look at it and let me know if I have it right?

    Thanks!

    LED30Wstrobe.png
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-