One-Shot help

Discussion in 'The Projects Forum' started by Napoleon, Dec 21, 2008.

  1. Napoleon

    Thread Starter Active Member

    Dec 21, 2008
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    Hello all!

    I'm looking for a one-shot with adjustable delay.
    Something like this:
    http://www.discovercircuits.com/DJ-Circuits/4013oneshots.htm
    (top one)

    It will be used in a 12v motor vehicle, so it should be able to work with a varying source voltage from the electrical system.

    The delay should be between 10ms to 100ms, adjustable.
    I dont need to be able to specify the exact value in ms, but perhaps a potentiometer of the correct value would allow for the adjustment range above.

    On this example circuit, can anyone suggest the proper values to obtain the delay adjustment range ?

    Also, do you think once adjusted, the delay will be fairly stable ?
    (meaning, will it be at the same set value throughout the life of the circuit)

    Or will I get random changing delays, but close to the original set point ?

    If it would not be that precise, how can its precision be improved ?
    Or perhaps it would be better to use a different circuit/approach altogether ?

    And, on that circuit, what would happen if the triggering switch is left on after the delay has passed ? Would it trigger again ? Or will it not trigger until the switch is released then pressed again ?

    Thanks for all the help!
    Sorry if I didn't explain this right...let me know if you need more info to help.
     
  2. Wendy

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    Mar 24, 2008
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  3. Ron H

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    Apr 14, 2005
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    You've told us what the delay range is, but is the output a pulse (if so, how wide?), or just a transition from low to high (or high to low)?
    What sort of input are you using to trigger the oneshot? Is it a switch, or the output of some electronic device? Is it a short pulse, or a voltage level transition? What is its amplitude?
     
  4. Napoleon

    Thread Starter Active Member

    Dec 21, 2008
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  5. Napoleon

    Thread Starter Active Member

    Dec 21, 2008
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    Hi Ron,

    Sorry for the missing bits.

    The output will drive a miniature 12v relay by the delay.
    The input will be from a momentary push switch.

    Basically, switch is pushed, relay goes on for the delay, then it waits for the next switch push. It should not repeat cycle if the switch is left pushed. switch has to go off, then back on before relay is turned on again.

    I hope that gives more info.

    I'll be playing with the 555 circuit Bill pointed out.
    Any other suggestions or advice/comments are certainly welcomed!!!
     
  6. Napoleon

    Thread Starter Active Member

    Dec 21, 2008
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    Hi Guys,

    So I breadboarded that 555 circuit Bill suggested and it works pretty good.
    Thanks Bill!!!

    I made a change to it, and would like some help with it if you guys spare some time.

    I am using a 22uf non-polarized (had it here) for Ct, and a 10K trimmer (in series with a 1K) for Rt. That should give me a delay range of about 266ms down to 24ms, right ?

    Now, here is what I would like some help with.

    1- It will be powered by a 12v car electrical system.
    2- The output of the 555 will drive a small device that will open a contact (Ex: relay)
    3- The device driven by the output must be normally closed
    4- The output will drive this device, plus the 2 leds currently on the circuit (maybe changed to dual color LED to save space??)
    5- The input will be triggered by a momentary push switch, and also from another circuit (a square wave signal, 50% duty cycle, 0-10v ?, when a specific frequency is reached, and beyond Ex: 400Hz, ideally the trigger frequency will be adjustable from about 400Hz to about 600)
    6- It will have a switch to power the circuit it on, and select between 2 trigger modes: Opto only, or push switch only.

    Ideas welcomed!!!

    Thanks guys!
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    Sounds about right. I'd double check the nonpolarized part though, it would be unusual to have a non-polarized cap that size.

    1. No problem, 12V will work.

    2. The schematic I showed would work for the relay.

    3. Relays have two sets of contacts, so this should be no problem.

    4. ??

    5. The first part no problem, the second, I'm not sure what you're asking.

    6. Not sure what you're after.

    Maybe you could let us know what you're trying to accomplish.
     
  8. Napoleon

    Thread Starter Active Member

    Dec 21, 2008
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    Hi Bill,
    Thanks again for the continued assistance!

    Ok, basically, I want to add this circuit to a motor bike.
    It will be used to temporarily turn off the ignition in order to do clutch-less up-shifting.

    The push switch part would be used on the shift pedal to cut ignition for about 65ms when shifting up, allowing the gears to sync and engage without using the clutch.

    The relay is simply going to break continuity on an existing kick stand switch that cuts ignition power when open.

    But, I would also like to have another mode of operation, in which the circuit will trigger when a particular RPM is reached on the engine.

    So:
    1- Ok on the 12 volt part.

    2- Ok for a relay, as long as it doesnt draw more than the 555 can drive, right ? (plus the draw of the LEDs)
    The relay will be 12v as well, and as small as possible. I've seen some really small reed relays, but I'm not sure how reliable these would be with the vibrations of the engine.

    3- I mentioend this becuase some are single throw, normally open, or at least a lot of the smaller simpler ones. I was also looking at solid state ones, but I think they are either too expensive, or typically normally open.

    4- I was just talking about the relay + the 2 LEDs here. And perhaps using a dual LED to save physical space on the monting box for the circuit.

    5- The second part of this is the triggering of the circuit based on RPM of the engine. This would come as a square wave, as that is what is sent to the tachometer. I would just be tapping into that signal to trigger the 555 once a specific frequency is reached (specific RPM on the tachometer).

    6- I was thinking here of adding a power switch to this 555 circuit that would toggle between totally off, On and triggered by push switch, and on and triggered by RPM/frequency. Perhaps an On-Off-On toggle switch.

    I hope this makes more sense now.
    Sorry for not having all the details you need to be able to help before.
    I'm sure I missed some things you might need.
    Let me know if I can explain anything else.

    Thanks!!!!

    Oh, and yes, it is an NP 22uf cap.
     
    Last edited: Dec 23, 2008
  9. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    #4

    "this device" ie. relay? with resistor and LED in parallel with coil. #5 Use a differentiator at pin 2 to give a - pulse for either pb sw. or data line. Data needs to be at least 10V pp or add transistor amp. # 6 use 2 pole 3 throw switch to control power and signal source.
     
  10. Napoleon

    Thread Starter Active Member

    Dec 21, 2008
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    Hi Bernard,

    Thanks for that.

    As for the triggering, I would need to interface to the existing variable frequency square wave signal somehow, and be able to specify and which frequency the 555 will trigger.

    Not really sure how to do that part.

    Its a square wave signal that will vary its frequency in relation to the RPM of the engine. I need to be able to adjust it, for example, so that the 555 triggers when that frequency is above a specific value, perhaps using a trim pot.. Ex: 500Hz

    Thanks for all the help!
     
  11. Ron H

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    Apr 14, 2005
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    The switch triggering is easy. The tachometer part is more difficult, and requires more parts. One way is to use an LM2907/2917 as a frequency-to-voltage converter. See p.8 on the datasheet. You can wire-OR its output (pin 5 in the schematic) with the switch on the shift mechanism.
     
  12. Napoleon

    Thread Starter Active Member

    Dec 21, 2008
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    Thanks Ron!
    That one looks like it should work perfect for this.

    I'll give it a shot.
     
  13. Ron H

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    Apr 14, 2005
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    :)
    Let us know if you need more help.

    I'm assuming that the governor is to limit RPMs if your shift does not happen in a timely manner. Keep in mind that there will be a small lag in the output of the governor.
    Could you also solve this problem with two switches? One would set a latch whose output would kill the ignition. The second would be positioned to sense a completed shift, resetting the latch and enabling the ignition.
    I had a friend who made one of these and put it on a pumped-up Yamaha YZxxx (can't remember) back in the late '70s. He got it to work, and was gonna run it at the drag strip, but IIRC he felt his construction was too sloppy, so he chickened out.
     
  14. Napoleon

    Thread Starter Active Member

    Dec 21, 2008
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    Hi Ron,

    Its not to limit RPMs, but rather, to kill ignition for a few ms so that a shift up can be made without using the clutch, and without throttling down.

    Basically, full open throttle, keep light pressure on the shifter, and when the circuit triggers, the transmission will simply fall into the next gear.

    This can be done now, but by reducing the throttle a little bit to un-load the transmission cogs so that the shift can take place.

    Having a circuit do this part will result in smoother up-shifts under power, even in turns.

    This is mainly to be used on the track, where there are high speed turns where you up-shift a few gears a full throttle.

    Thanks everyone for all the help.
    I should have enough here to keep me busy experimenting with a few things.

    I just had another question...
    Is there a recommended method to tap into the existing RPM signal wire without causing any ill effects on either this new circuit or the existing RPM metering on the bike ?

    According to the service manual, it should be a pulse train that shouldnt exceed 0-10v pp.

    I just want to make sure this new circuit i will be adding will not disrupt the normal operation of that existing circuit in any way, even if this new circuit has a short or other malfunction.

    Thanks everyone!
     
  15. Ron H

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    Apr 14, 2005
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    I understand why you are doing this. As I said, a friend successfully did this in the '70s.
    I thought the purpose of the switch is to trigger the oneshot, which will kill the ignition. If so, what is the purpose of the governor (RPM trigger)? Is it just over-rev protection?
     
  16. Napoleon

    Thread Starter Active Member

    Dec 21, 2008
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    The RPM trigger is so that I can trigger the ingnition kill at the best spot on the RPM range.
    This way I eliminate human error.

    I can find the best RPM for the upshift (based on optimal torque curve), then calibrate the trigger to that RPM.

    That way, I can get consistent shifts, always at the RPM I intended.
    As opposed to eye-balling it.
     
  17. Ron H

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    Ok, I actually thought about that. It sounds great for a straight track (drag strip), but I figured you wouldn't want to be surprised by a shift on a curve. I suppose you know by engine sound when the shift is about to occur.
     
  18. Bernard

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    Aug 7, 2008
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    Here is my version of a speed detector. Add to previous ckt. The IC shown is LM 311, any other comparator should work. If the .001 cap is not enough isolation ,can add one transistor amp.
     
  19. Napoleon

    Thread Starter Active Member

    Dec 21, 2008
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    This will be used to shift in high speed turns, not just straights.
    The idea is to set the delay precisely so that the bike is not upset when the up-shift happens. Typically about 65ms.

    Part of the plan (if this circuit goes well) is to expand it so that the circuit will be aware of the current gear, and be able to pre-set a different delay fr each gear, as they do need to be slightly different.

    Also, I will be testing all this with 2 switches + the frequency trigger in different combinations.

    Ex: RPM trigger + push button required for the ignition cut. If either one is not triggered, the ignition is not touched.

    Another switch will be on the shift lever, so in one mode, it will need the RPM trigger plus this switch (or the push button switch), and in the other mode, it will be just the shift lever switch (basically shift at whatever RPM).

    I will be testing all this out to determine the best delay and switch operations.
     
  20. Napoleon

    Thread Starter Active Member

    Dec 21, 2008
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    Hi Bernard,

    Thanks for the circuit.
    It sort of makes a little sense to me (i'm slow).

    Would there be any benefit to going with one circuit over the other (from the ones suggested on the thread by others)

    In the end, I would like to look for the most reliable, with the least amount of components/simplest.

    Thanks!
     
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