2 led timed circuit

Discussion in 'The Projects Forum' started by brozizds, Aug 15, 2010.

  1. brozizds

    Thread Starter Active Member

    Aug 15, 2010
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    I am trying to build a 2 led timed circuit for cooking purpose green to show start and red at the end (with a piezo buzzer when complete). I would like to stack about 8 of these circuits at different timed intervals.can someone help with a schematic and parts list?
     
  2. Wendy

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    Mar 24, 2008
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    The 555 Projects

    555 Monostable

    This is a start. I'll draw something a bit more complete up in a bit.

    Instead of 8 different devices why not have switches and 1 device? If this is a no go say so.

    We need time durations also if you want complete schematics.
     
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  3. brozizds

    Thread Starter Active Member

    Aug 15, 2010
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    first thanks my timed circuits are as follows ,3 min-6min-7min-8min-8.5min-9.5min-10min I would like to have green led at start and red led with piezo buzz at end for each timer thank you for your help
     
  4. Wendy

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    Did you read the 555 monostable link? It has most of what you're after, minus the buzzer (which is extremely simple).

    The question is whether you could follow it enough to use?

    Also, do you really need 6 discrete timers, or would one programmable work?
     
  5. Wendy

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    On another thread (Short Beep Tone with LM555) I came up with this. Your application is different, and would require a different layout.

    [​IMG]
     
  6. brozizds

    Thread Starter Active Member

    Aug 15, 2010
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    Bill, I think I will need 6 timers because they may all be on at the same time and I think I will need a start switch and stop switch to shut off red (2nd led)and buzzer these timers will be used for cooking. ps my knowlege is very limited on this subject but I do like working on these kind of projects
    Thanks
     
  7. Wendy

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    OK, instead of a fixed duration timer you could calibrate the time by putting a pot with a knob in front. This will reduce the number of timers you need.
     
  8. brozizds

    Thread Starter Active Member

    Aug 15, 2010
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    Bill, for now i just need one layout for the project im working on as I explained in my first post Thanks :)
     
  9. Wendy

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    OK, I'll have something up in a couple of hours.

    Correction, in a day or so.
     
  10. Wendy

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    OK, obviously I have not built this.

    [​IMG]

    Parts List

    U1 - 555
    Q1 - 2N2222A NPN Transistor (or PN2222A)
    Q2 - 2N2907A PNP Transistor (or PN2907A)
    D1 - Red LED
    D2 - Green LED
    9V Battery and Clip
    Sonalert
    S1 - SPST normally open momentary contact switch
    S2 - SPST normally closed momentary contact switch
    Ct - 1000µF Capacitor
    C1,C2,C3 - 0.1µF Capacitor
    R1,R2,R5 - 1KΩ 5% ¼W Resistor
    R3,R4 - 10KΩ 5% ¼W Resistor
    Rt - User test select

    3 min - 164KΩ (150KΩ + (13KΩ or 15KΩ)
    6 min - 327KΩ (330KΩ or 300KΩ + 27KΩ)
    7 min - 382KΩ (390KΩ or 360KΩ + 22KΩ)
    8 min - 436KΩ (430KΩ or 430KΩ +6.2KΩ)
    8½ min - 464KΩ (470KΩ or 430KΩ + 33KΩ)
    9½ min - 518KΩ (510KΩ or 510KΩ + 8.2KΩ)
    10 min - 545KΩ (560KΩ or 510KΩ + 36KΩ)

    Or you could use a internal variable resistor for Rt and tweak the timer duration much closer to your specs.

    Half the capacitance, double the resistance. While the timer is very repeatable capacitors are typically only 20% accurate, so you will likely need to tweak it anyhow to get the duration correct.

    I have used elements of this in other designs. Q1/Q2/R5 make a SCR, which can be bought as a complete device. Since I don't generally have one handy I make it with discrete parts.

    Things like the Sonalert and batterys can be shared. Since you seemed to indicate they were going to be in separate boxes that is how I drew it. If you want to merge any parts the design will need tweaked a bit.
     
  11. brozizds

    Thread Starter Active Member

    Aug 15, 2010
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    Thanks bill i will get the parts and do a prototype . I do like the idea of a variable resistor and the possibility of using a SCR but I dont have enough smarts in this field l will most likely wire the transistors wrong after 38 years of construction not electronics thanks again
     
  12. Wendy

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    The SCR is fairly necessary. It will trip when the LED goes red, and stay on until the "Silence Alarm" button is pushed. Just keep track of which transistor is which and you'll be fine.

    You could just wire the sonalert from Vcc to pin 3 and put a toggle switch in line with it. It would be simpler.
     
  13. brozizds

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    Aug 15, 2010
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    bill im having problems locating all the parts i need do you have any suggestions . i need a bit more help! thanks
     
  14. Wendy

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    What parts in specific? I can design around a lot if I know where the problems are.

    What part of the world are you. You'll note most of the regular members have a location in their profile. This is to address the parts issue for the most part, and to let you know when they are likely to be up and out of bed. I'm an odd duck on the latter, since I work third shift.
     
  15. brozizds

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    Aug 15, 2010
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    pennsylvania. bill im still shoppin radio shack tdy i'll get back to you thank you. ps i did edit my prof
     
  16. Wendy

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    Radio Shack is expensive, though they have all the parts. I used them for my articles because they are convenient, but my main sources are stores in Dallas. Dallas is unusual in that we have more than 1 electronic component outlets, not counting places like Fry's.

    I strongly suggest you only use Radio Shack for quick turn around. For quantity go with BG Micro, Digikey, or Mouser's. You will save over 50% or more in parts.

    There are a few items Radio Shack is competitive, but not many. Battery holders, for example, they can't be beat. They also have transistor packs that aren't too bad a deal, though I can buy PN2222A/PN2907A (equivalent to 2N2222A/PN2907A) for 8¢ ea from BG Micro, or 51¢ or less from anyone else.

    Cases or boxes are not great at Radio Shack, but they are in the running. You could pack one of these circuits in the space it takes to hold 3 9V batteries (including a 9V battery), so you can get a bit creative as to what you use.
     
    Last edited: Aug 22, 2010
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  17. marshallf3

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    Jul 26, 2010
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    As they have started renaming themselves as "The Shack" and changing their image I'm finding less and less parts avaialble at the nearest one to me. Most people that work there aren't exactly that bright either (except on high-$ cell phones and Dish receivers) so it can be a frustrating experience.

    One day I was looking for something and have learned to call to check availability first. I must have got a hold of a visiting regional manager as he told me that while they didn't stock them there, the store at "Y" should have them. He went on to explain that he only kept a very limited stock of parts at most stores but a fairly full line at just a certain few others around OKC and gave me the locations of those to write down.

    It's sad, what was once a half-decent source has all but reduced themselves to items that can be found elsewhere cheaper. I miss things like being able to buy coax by the foot, the bags of assorted inductors that actually were nice, big assortments, a choice of resistors, caps, pots etc that covered a much better range of values and more than just a couple of transistors and ICs. Shoot - the one near me doesnt even carry project boards or enclosures anymore which makes me surprised that they actually have LEDs.
     
    Last edited: Aug 22, 2010
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  18. brozizds

    Thread Starter Active Member

    Aug 15, 2010
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    Bill, I picked up the parts tdy. but I do have a few to check with you. I got all from our local radio shack 1. 555cn Timer IC #276-1723 (has 8 pins but diff conf from your schemaitc and no marks for up dwn)HELP?2. transistor pn2907-Type but no A on the end(PNP)#276-2023. 3.Transistor MPS2222A NPN, #276-2009. 4. LED 5mm red 1.7V 20mA 3000mcd #276-0304. 5. LED 5mm green 2.1V 30mA 630mcd. 6. mini piezo buzzer #273-074A(no sonalert avaible) 3.0-16VDC 4.1kHz 7mA. 7. 1000uF Electrolytic Capacitor # 272-1032. Can I use these with your schematic? thanks again for your help. Jim
     
  19. Wendy

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    I'll be back, but refer heavily to the 555 Monostable experiment, it really does spell everything out (and lays it out besides).
     
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  20. brozizds

    Thread Starter Active Member

    Aug 15, 2010
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    Bill , the 555 I picked up at RS has no notch on outer case to set direction. the schematic on the plastic pack shows pin arrangment as on the 555 inside pack and shows a notch as in your schematic Thanks Jim
     
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