Beginner 555 Timer

Discussion in 'General Electronics Chat' started by TexAvery, Oct 7, 2009.

  1. TexAvery

    Thread Starter Member

    Oct 7, 2009
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    Hi, This is my first post. I am a neon artist and in need of a 555 timer circuit to be added to my existing project.My problem is the sensor only turns on the motor for 1 second then resets.
    Apparently I need to add a timer, I would want about 1~3 min or so with some adjustment As you can tell I do not know much about electronics, just the very basics. Anyway, I can pay for a schematic, I can get the parts myself. Just let me know if your interested. This is what I have so far.
    [​IMG]
    Thanks Tim Walker
     
  2. Wendy

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    Mar 24, 2008
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    No money is needed. What is your sensor? We can design around that.

    My article, 555 Monostable shows the basics. We can add to that.

    You'll find you've entered a den of problem solvers here, money isn't an issue, though I doubt if anyone is adverse to it. :)

    Also, what is the voltage/current of the motor, and what kind of load is it pushing?
     
  3. TexAvery

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    Oct 7, 2009
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  4. Wendy

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    OK, so what is the power supply your using for the sensor? We also need more information on the motor, as in current and voltage. The reason I was asking for how big a load it is turning is that determines surge amps.

    You planning on soldering this together?

    I gotta say, this one is pretty easy as far as it goes.

    Couple of points, I think that MOSFET will need more voltage (I'm surprised it works at all), can you use a 12VDC power supply? We can use a simple regulator circuit for the sensor. I could just thow a simple version out and see if it works, if not we'll modify it for more voltage.
     
  5. TexAvery

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  6. Bernard

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    Aug 7, 2008
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    This was done before, may be close to what you need. The web address would not respond, but found by going to Bernard, List all posts, down to about page 7, pbalien73,How do I hook this up? 6-29-09, 10:58. A 2N3904 can replace MPSA13,was supplied.Depending on motor drain, might eliminate darlington D1326. was driving a 1 A load. Output of PIR is 5 sec + pulse, may be similar to yours. The PIR did not like battery dip at light turn on, even with 100μF decoupling,not shown.A outboard regulator for PIR corrected problem.
     
  7. Wendy

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    [​IMG]

    Like I said, I'm not comfortable with Q2. The only reason it may not be getting hot is the short amount of time it is on. This is because you need it like a switch, but with the low voltage on the gate it is linear, not quite all the way on or off. My advice is try it and see.

    This circuit will go to 4 minutes. If you need more up R3 24-27KΩ per minute needed.

    A 555 monostable responds to negitive going pulses, your sensor has a postive going pulse, so I added Q1. This circuit will ignore the sensor until it is finished timing, which may not be what you want.

    Let me know if you need any changes.
     
    Last edited: Oct 7, 2009
  8. SgtWookie

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    Jul 17, 2007
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    An IRF510 MOSFET requires a Vgs (voltage from the gate to the source) of 10v in order to be fully turned on.

    Maximum output voltage for a bjt (transistorized) 555 timer is Vcc - 1.3v under light loading; in your case 4.5v - 1.3v = 3.2v. That is not enough to turn on even a logic-level MOSFET.

    However, if you went to a CMOS 555 timer and a logic level MOSFET like an IRL510 or IRLZ14, IRLZ24, etc. - that would work.
     
  9. Wendy

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    Might be easier to go with a conventional BJT transistor, like a 2N3055.
     
  10. TexAvery

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    Oct 7, 2009
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    Replace the IRF 510 with 2N3055?
     
  11. Wendy

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    Yes.

    You'll note I put a resistor R5 in front of the gate. Replace it with a 180Ω (assuming a 5VDC power supply) and the 2N3055 and it will work the same. A Darlington transistor, and Bernard said, might be better. Think TIP120.

    I mentioned it in passing, but do you need this circuit to start from scratch every time it sees movement? This design will ignore further input until the timer is finished (and the output goes low).
     
  12. SgtWookie

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    Reading the website for the fans, they say that they will run for about 2 hours with the three AAA batteries they supply. That suggests an average current draw of around 250mA, but the surge current at the beginning will be considerably higher; perhaps 8x as much. That will look like a momentary dead short to the batteries.

    You may wind up needing a separate power supply for the PIR sensor.

    If you replace the IRF510 with a 2N3055, you will need to change the 1k resistor to about 51 Ohms (1/2W) in order to allow saturation of the transistor. You will lose about 0.4v across the transistor. Base current will be around 40mA.

    If you replace it with a TIP120, you can use a much larger value resistor (around 200 Ohms) for a 10mA base current, but you will lose a volt or more across the transistor. This may prevent the fan from working at all.
     
  13. Wendy

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    OK, I could get around some of that using a Sziklai Pair. I'll wait for feedback from the OP and redraw the schematic based on the input.

    I notice you think he's using a fan. I haven't seen that anywhere, I suspect he's wanting to do something he wants to keep propriety.
     
  14. SgtWookie

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    Good plan.
    Check out his reply #5, the 2nd link; same as this one:
    http://www.flashingblinkylights.com/ledminifans-p-1400.html?gclid=CJf4jMb4q50CFSn6agodoyJ1iQ

    Note the comment about 2 hour battery life right above the shipping weight.

    The DC motor and the blinking LEDs will generate a considerable amount of noise on a battery supply, particularly when starting up. I don't think that just some large caps will be enough to smooth things out.
     
  15. Wendy

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    In that case I'd better tweak battery life considerations (CMOS 555 and all).

    Thanks, I'd missed it.
     
  16. SgtWookie

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    If you're going to use a CMOS 555, it's going to have very puny source/sink current abilities. Even 1mA source/sink will cause about a 0.5v drop.
     
  17. Wendy

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    Yeah, the transistor will have to make up for that. I didn't realize he was using batteries though, it makes a difference.
     
  18. Bernard

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    Aug 7, 2008
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    What I saw was a 1 A AC operated supply, my bet is that motor draws about 100 mA.if all of the LED's are eliminated. As the PIR may only draw about 400 uA, could add 680 ohm between PIR and motor with cap on PIR side. And with 1A supply there may be no problem with power dip.
     
  19. TexAvery

    Thread Starter Member

    Oct 7, 2009
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    Nothing propriety, just a painting of a man with the eyes cut out and replaced with LED fans that give a strange effect. Here is the history on this simple project. I originally used a off the shelf motion detector from Home Depot, the kind that fits in a single gang box.One problem is the 2 fans (sorry I forgot to mention there are two) do not turn off (pulse on & off) when sensor time is up. My guess.. not enuff load. So, I added a 10w incandescent bulb to the circuit and now it works fine, but wrong way to go about it. Also a 4.5 vdc transformer is needed, again backward engineering.Now I want use the AC to 4.5vdc power supply instead of 3 AAA batteries, and power a motion sensor that is easier to conceal. With all the help I really feel the need to PayPal someone. Or help with a neon project in return.
    Thanks
     
  20. Bernard

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    When you get it all puttogether and give us a final report would would be appreciated. Great Home page.
     
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