30-50htz generator

Discussion in 'General Electronics Chat' started by adamclark, Jun 21, 2014.

  1. adamclark

    Thread Starter Member

    Oct 4, 2013
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    hello all.. I find myself needing to build a 30-50htz squarewave generator. I have a drawing for from a site for this but I wanted some of the gurus gere to look it over before I build it. thank you
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,498
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    Take a small transformer and square up the sine wave, or use as a clk, if for the US you need 30Hz divide the 60/2.
    Max.
     
  3. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,343
    Hello,

    The schematic you are showing us is for an automotive modification.
    You know that any automotive modifications are not allowed over here.

    If you want to make a 555 oscillator, have a look in Bill's blog:
    http://forum.allaboutcircuits.com/blog.php?b=378

    Bertus
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,766
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    Do you mean a selectable fixed frequency within that range, or a frequency which automatically sweeps form 30-50Hz (and if so, over what time interval)?
     
  5. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
    6
    the schematic is from an automotive mod.. My intention is not for an auto mod, even if the reference is.. I am merely using the vats system from a car for a key operated security feature for a project. and the vats sytem is perfect for my application.. sorry for not being more specific..
     
  6. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
    6
    it has to be 30hz.. that was the next question I had. some use 50hz, mine is 30. but there is only 1 drawing. here is a snippit from the article. I claims the 22k resisitor between pins 6 and 7 change this.. what frequency is the one in the drawing and how is this value figured?
    "It produces a 50 HZ square wave 50% duty cycle pulsed ground signal. Just get a 555 timer IC and connect it up as follows. A small IC circuit board from RadioShack can hold the 555 and most of the other components.

    Parts:
    555 timer
    16 pin DIP IC PC board
    two 0.1 µF ceramic capacitors
    1 µF electrolytic capacitor
    3.9 K resistor
    22 K resistor
    100 Ohm resistor
    14 Volt Zener diode
    Plastic enclosure

    Pin 1 is Ground. Pin 8 is + input. Connect a 0.1 µF ceramic cap between these
    pins, with short leads, for filtering. Otherwise it may misbehave. Connect pin
    8 to 100 Ohm resistor. Connect a 14V Zener diode between pins 1 and 8, banded (+)
    end to pin 8, to absorb voltage spikes from starter solenoid or system overvoltage.

    Other end of 100 Ohm resistor connects to ECM's "ignition on" signal wire.

    Tie pin 4 to pin 8.

    Tie pin 6 to pin 2.

    Add a 3.9K resistor from pin 7 to pin 8. (A 3.3K will be close enough)

    Add a 22K resistor from pin 6 to pin 7. (You could adjust this one for
    precision setting, but it's not needed for this application)

    Add a 1 µf capacitor (electrolytic OK) + side to pin 6, - side to pin 1.

    Add a 0.1µf cap from pin 5 to pin 1.

    Output is on pin 3. Connect to VATS wire of ECM. Also connect
    alarm to ground this pin to disable fuel delivery when armed. "
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
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  8. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
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  9. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
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    after looking at the datasheet I see the max voltage for the 555 is 16v. so I guess it would work,, but will the added voltage change the freq. or duty cycle?
     
  10. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
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    and would it be possible to connect 2 LEDS to show the occilation also?
     
  11. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,766
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    at 30 Hz you would have trouble seeing the LED's due to the flicker response of the human eye being less than that, at around 15 to 25Hz. Add another divide by two circuit for the LED's to get the flicker rate low enough to see. or just be satisfied that if the LED's are lit, the the circuit is 'probably' working correctly.
     
  12. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
    6
    that's what I was shooting for.. after I said it I thought about that.. my o scope will show me the freq. but im not sure how to set it to check the duty cycle.. I just wanted to light an LED from the output to show actual output..
     
  13. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
    6
    oh.. and im doing this in a pinch and esco isn't open tomorrow.. im sure ive got everything on the parts list, but would anyone care to tell me how to tell a 14v zener diode from a drawer full of them? and the same with figuring out what size ceramic caps are? thanks
     
  14. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,965
    743
    zeners usually have the voltage on the case, if it dosen't you will need a 30V psu and a 1K resistor in series across the psu, then measure the voltage across the zener.
     
  15. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
    6
    cool..that worked so I have a 14v zener.. now I need 2 0.1uf ceramic.. I have a bunch of them in a container.. is there an easy way to find value of these? I have a chart showing what the numbers are supposed to mean,, but the numbers on these match nothing.. p.s. thanks for the tip on figuring out the zener... wont forget that one
     
  16. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    0.1uF = 10 x 10^4 pF, so it will probably be marked as '104'. Alternatively it may have coloured bands: brown, black, yellow.
     
  17. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
    6
    I have 2 labels 103... what size would those be?
     
  18. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
    6
    ok,, so I built the exact drawing without changing anything.. on my scope it is squarewave at 28.63hz and another number ther is 50.30. its also 4.8v.. Im assuming that the duty cycle...so I belive this should work.. can I put an led on the 30hz output to show that is actually working? I know at 30hz it should appear to flash rapidly, but that would be good enough for me to know its working
     
  19. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
    6
    ok.. so I put an LED between the out and the ground.. it changed to duty cycle to about 70/30 at 5.67hz... not the right thing to do.. any ideas how to make the led work? and at 30hz I couldn't even tell it was flashing
     
  20. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,766
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    Did the LED have a current-limiting resistor in series? If not, it's not surprising the frequency changed; and you may have cooked the LED.

    = 10 x 10^3 pF = 10nF = 0.01uF
     
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