How to make rapid 12v pulse?

Discussion in 'The Projects Forum' started by ohiopsd, Oct 21, 2009.

  1. ohiopsd

    Thread Starter New Member

    Oct 21, 2009
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    I have a project, need to make a piece of test equipment that sends a 12v signal about 30 times per second. I figure a circuit of some sort would be best here.
    And if there was a way to make the pulse adjustable, that would work great. Need to figure out exactly what pulse would work best for the tester, I'm guesssing at 30 pulse/sec now. Would it be a simple device adjustment, or would it entail starting over with other electronics components?

    I am a beginner at electronics but have a basic understanding, love to learn and am very hands-on.
    Thanks for any help.
     
  2. bluebrakes

    Active Member

    Oct 17, 2009
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    a 555 timer should be more than suitable for this project and it's perfect for beginners. Is it just a solid square wave pulse you want to send?

    Putting variable resistors in the circuit will enable you control of the pulse too.
     
  3. ohiopsd

    Thread Starter New Member

    Oct 21, 2009
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    Ummm, sure. Ok. Just need to turn a solenoid on and off really quickly.
    Any examples of actual components and boards of this nature would be great.

    Thank you.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    What is the voltage and current required by the solenoid? AC or DC current?
     
  5. ohiopsd

    Thread Starter New Member

    Oct 21, 2009
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    12v DC, automotive related. Amps, not really sure, a few I guess. How can I check to get a better answer for you?

    Edit: Sorry, I see now you didn't ask about amps...
     
    Last edited: Oct 21, 2009
  6. SgtWookie

    Expert

    Jul 17, 2007
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    Yes, I did. "Current" is measured in Amperes.

    Is this for a transmission pressure control solenoid?
     
  7. ohiopsd

    Thread Starter New Member

    Oct 21, 2009
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    No, fuel injection solenoid. 30 pulses per second might not be possible with 12v, they run at 120v normally, I was trying to keep the project simple. I know the solenoids will still activate with 12v, I do it manually with a switch all the time. I would like to have something that will pulse them very quickly, quicker than I can flick a switch on and off repeatedly.
    Thanks.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    120v??? Usually, fuel injectors are more like 2v-3.5v?

    OK, how wide do you want the pulse?
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    Anyway, here's one circuit to generate a 30Hz input.
    The pulse is roughly 32mS wide.

    See the attached.
     
  10. ohiopsd

    Thread Starter New Member

    Oct 21, 2009
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    Early versions were 100v, then they were oem bumped to 110v, then 120v. We change a resistor in some of the electronics to bump to 140v. Makes them real snappy.

    As far as pulse width, I'm not real sure what's best for this. I wanted 30 pulses per second to simulate running them at 1800 rpm, actual operation of the injectors is somewhere around 2 ms at 1800 rpm. But that's with 100v - 120v too, so 2 ms at 12v might not even be possible with these. Like I said, if there's a way to make it flexible, that' be great. But if these things' were easy enought to build and/or modify, then I look forwrd to trial and error to see what actually works!
    I am not necessarily trying to duplicate running parameters (unless it's not that difficult to do). I just need to activate them quickly for a half minute or so for this test.

    Would you have a legend of sorts (or good resources) as to what your diagram is explaining? It's been years since I could decipher one of these and I'd love to read up on the lingo again.

    Thanks for all your help.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    OK, if you want 2mS, then R1 should be increased to 22k, and R3 increased to 680 Ohms.

    A table of electronic symbols is here:
    http://library.thinkquest.org/10784/circuit_symbols.html

    U1 is a generic 555 timer. Various prefixes for them are LM, NE, SE, and many others. In this case, you do not want one that has the character "C" in the prefix.

    "Rn" components are resistors.
    "Cn" components are capacitors.
    "Dn" components are diodes.
     
  12. ohiopsd

    Thread Starter New Member

    Oct 21, 2009
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    Excellent!
    I'll look everything over and let you know if I have any other questions.

    Thanks.
     
  13. ohiopsd

    Thread Starter New Member

    Oct 21, 2009
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    OK, a few questions.
    What does vcc stand for?
    It looks like we're supplying 12v to the solenoid (and to the 555), then controlling the ground to the solenoid for the pulses, correct?
    Are you showing an ammeter in the middle of the schematic? If so why? And if not what is the A circled?
    What is the value for R6?
    Q2 appears to be a NPN transistor, correct? What it it's value? (that whole area of the schematic is a little fuzzy for me read values.)

    Lastly, how do you firgure what changes to make to R1 and R3 to vary the pw? If it's not that simple of an answer, then don't bother. ;)

    Thanks!
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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    The supply voltage for a circuit is often given as V plus a double-letter suffix. The double letter is usually related to the lead of the transistors that are commonly connected to that supply or to a resistor that connects to that supply.
    Yes.
    The voltage waveform at "(A)" is shown in green on the simulated O-scope, below.
    R6 is a 120 Ohm, 2 Watt resistor. It must not be a wirewound resistor.
    If you click twice on the schematic, you'll see it toggle between "fit to screen" and "full size".
    Q2 is a 2N3055 NPN power transistor.

    I simply "tweaked" the values in the simulation a bit. ;)
     
  15. shortbus

    AAC Fanatic!

    Sep 30, 2009
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  16. SgtWookie

    Expert

    Jul 17, 2007
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    From a PM:
    The coil will "ring" a bit when Q2 is suddenly turned off. D3 provides a current path so that the reverse voltage across Q2 won't be more than about 1 volt.
    C1 is the timing capacitor for the 555. C2 slows the voltage rise time across across D3, lowering it's peak current flow.

    Power IS run straight to the solenoid. When the current flow through it is suddenly turned off by Q2, it'll try to keep going. This can result in very high peak reverse voltages. D4 provides a current path for this high voltage pulse; keeping it down to around 1v.
     
  17. ohiopsd

    Thread Starter New Member

    Oct 21, 2009
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    That all actually makes sense!

    Thanks a lot.
     
  18. ohiopsd

    Thread Starter New Member

    Oct 21, 2009
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    Ok, been a while but I'm getting back to this project.
    I went to order some parts and there are a ton of options. I'm looking for input as to how to narrow down what I should get to try this out.
    For example:
    Resistors: watt, composition, tolerance?
    Capacitor: Bi-polar? Polarized? volts, tolerance, ESR?
    Diode: Volts, Reverse and/or Froward, speed, capacitance, etc.
    Transistor: Vce @ Ib, Ic?
    555: SOIC vs SOP, 200 ma or 6 ma, bi-polar?

    Thanks with any help on this.
     
  19. Theboxmodder

    New Member

    Jul 31, 2010
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    I'm currently looking for a circuit to modulate a pulse to a Transmission Pressure Solenoid. I have a 555 IC so I'm looking for that platform. But I can always visit Mouser.

    I saw the post on the Torque Converter Lockup. My solenoid controls the shift. Full 12v current lets no fluid (Blown transmission.) by and 0v lets it all by (Very hard shifts.). I want to be able to modulate the current to let say 45-70% fluid by based on throttle position. Then when WOT full line pressure. I'm going to assume the modulation is 100hz?
     
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