Need help on 555 timer/LM 3909 (MIRINGU)

Discussion in 'General Electronics Chat' started by SgtWookie, Sep 8, 2008.

  1. SgtWookie

    Thread Starter Expert

    Jul 17, 2007
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    While it certainly isn't a crime to send a private message, it is most certainly not my preferred method of providing assistance here.
    Communicating via PM completely excludes anyone else from benefitting from the exchange, effectively defeating the purpose of the Board.
    PM exchanges also eliminate the possibility that you may benefit from other informed responses.
    I don't give out my E-mail address, because I would be inundated with requests. I simply cannot let that happen.

    As far as your circuit is concerned, the LM3909 is very different from the various versions of 555 timers. It can operate normally on voltages far below the requirements of a 555.

    If you wish to replicate the function of an LM3909, here is a page that describes how to build one out of discrete components:
    http://home.cogeco.ca/~rpaisley4/LM3909.html

    If you are insistent on using a 555 timer, you will need to use a completely different circuit.

    Post your circuit so that we can see what you are attempting to do.
     
  2. MIRINGU

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    Mar 18, 2007
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    Thanks, the cct is here.If this thread is not visible to other members i've duplicated it in http://forum.allaboutcircuits.com/showthread.php?p=82990#post82990)
     
  3. SgtWookie

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    The circuit that you have attached cannot work. There is no source of power or current path to either LM3909 IC, only to the AND gate.

    [eta] Unless, of course, you meant to connect Vcc to the wire that goes to the pot and both pin 5's of the LM3909's instead of hopping over it.
     
    Last edited: Sep 12, 2008
  4. MIRINGU

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    Mar 18, 2007
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    Yes pin 5 is the vcc fed to LM3909.I made a mistake in the diagram(hopping over)
     
  5. Wendy

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    Mar 24, 2008
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    I've been thinking about something similar, not building a LM3909, but coming up with some circuits that will do something similar (ie, flash a LED for 2 years using a single D cell). I feel it is futile to wire a chipie, they can be wasteful using parts because, well, it doesn't really cost anything. It might be worth studying the 3909 to see how they do it though.

    **********

    Re-examining the chip though, sucker is simple, isn't it.
     
  6. SgtWookie

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    Hi Bill,
    Have a look at the link I posted when I started this thread. It shows a couple of ways how to build an LM3909 replica using discrete components, and also shows how the circuit works. It's basically a switched-capacitor voltage doubler.

    Our OP here (MIRINGU) wants to replicate the function of an LM3909 using a 555 timer. However, they are very different critters. The resulting circuit would be very different from what he has now. However, if he would build two copies of Rob Paisley's LM3909 emulation circuit, he could adapt that directly to his schematic.

    Looking back on the other two times he's brought this circuit up, I've also referred him to Rob Paisley's 3909 replacement using discrete components. So, this is the third time I've referred him to exactly the same page.
     
    Last edited: Sep 13, 2008
  7. SgtWookie

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    Well, I just finished fiddling with a simulation of Miringu's schematic, and it still won't work; even with connecting up Vcc properly. There's no connection to pin 6 of IC1, so it doesn't do anything; just sits there. Therefore, there is never any output from IC1, so the NAND gate never gets two true inputs - so it always has a high output, and no sound.
     
  8. Wendy

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    I've looked at the site (again), bookmarked it as matter of fact. I keep thinking ICs are complex, then look at that sucker again to change my mind.

    I'm still hooked on the .7V drop on the BE, it amazes me they got this sucker to work, and even more they decided it wasn't worth reproducing.

    I'm still debating how to create a voltage doubler with a 7555, so you can flash a LED with a high Vf from 3V. The discharge pin may offer a way, but I haven't quite figured it out yet. The LM3909 does provide a good model though.
     
  9. SgtWookie

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    Well, the LM3909 really wasn't designed to flash a high-voltage LED; just one of the standard voltage critters (up to about 2.1v).

    For your situation, you could probably use a couple of FETs and a Schottky diode to swap the connections around on a couple of capacitors, making a charge pump.
     
  10. Audioguru

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    Dec 20, 2007
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    My 3V Ultra-Bright LED Chaser project still works when the battery has dropped to 2.0V and less.
    It uses 1.8V ultra-bright red LEDs and 74HCxx ICs that have plenty of output current and a minimum supply of 2.0V.
    It doesn't double the battery voltage.

    My 6V Ultra-Bright Chaser project is almost the same except the LEDs are 3.5V blue ones and the circuit still works when the battery has dropped to 4V.
     
  11. SgtWookie

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    Audioguru,
    Care to post links to your projects, or put them in the Projects forum, in case other readers might wish to try their hand?
     
  12. Wendy

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    I'll second that, LED circuits are always useful. If you don't mind they would be a good addition to the upcoming cookbook.
     
  13. Wendy

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    How many other chips run off of 1.5V? The LM324 will run off 2V, but that is as low as I am aware of beside the LM3909.

    I think I have figured out how to do with a CMOS 555 and the discharge pin, just make a narrow duty cycle astable and a capacitor. Using 3V it should handle the newer LED's.
     
    Last edited: Sep 14, 2008
  14. SgtWookie

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    You could always make a Joule Thief instead.
    http://www.bigclive.com/joule.htm
    Very few parts. The thing will run on batteries so discharged that you would normally toss them out.
     
  15. Wendy

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    The point is to run a flasher for 2 years off D cells. Not very effective with that gadget.
     
  16. Ron H

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    Bill, what battery chemistry are you wanting to use for your 2 year flasher?
     
  17. Audioguru

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    If you blink an LED for a short duration a few times per minute and the circuit has a very low operating current then a battery will last for years.
    An alkaline D cell.
     
  18. Wendy

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    I was thinking of Alkaline, KISS. I'd love to use one, but at this point it is an intellectual excercise.
     
    Last edited: Sep 16, 2008
  19. Wendy

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    OK, here is the low voltage LED version. I'm going to try a high voltage LED version. R3 can be adjust to whatever the LED needs. On a high voltage red LED I'd probably use 5Ω or so. I was aiming for 30ms pulses for persistance of vision, and a 2 second pulse rate.

    [​IMG]
     
  20. MIRINGU

    Active Member

    Mar 18, 2007
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    Thanks,
    since am not familiar with simulation i was "guessing" if could be compared like this ,
    LM3909 -- 555 timer
    For IC1
    2 - 3
    4 - 1
    5 - 4,8 together
    8 - connect 2,6 together

    For IC2
    2 - 7
    4 - 1
    5 - 4,8 together
    6 - 3
    8 - 2,6 together
    the others i ignored,can this "guess"funtion when simulated?
     
    Last edited: Sep 16, 2008
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