Need Help

Discussion in 'The Projects Forum' started by Jure George, May 17, 2010.

  1. Jure George

    Thread Starter Active Member

    Dec 28, 2008
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    Hello, I need a circuit that I can put together with regular I.C. I don`t want to go to the PIC route yet as I am not reading for that learning curve yet and this is a very small production run, 1- 4 boards.

    I am into R.C submarines and I need a circuit that when it detects that the transmitter signal, 75mHz FM is missing, then the circuits turns on and runs for a user set time, a small D.C. pump, 1 Amp max.

    The set run time is done by a variable pot by the user from on instantly from detection of No signal to 30 sec. max. ( 0n instantly - 30sec. run max. )

    The only way to reset the system would be to turn on/off the main power by the operator. The main battery is 6v - 12v max.

    If there is No loss of signal then the circuit lets the signal pass through to allow normal use of submarine. So it would go between receiver and pump motor, the pump motor should also be able to run on command of operator.

    I hope someone can show me a working circuit with all the parts listed so that I could put one together and try it out.

    Thanks In Advance for your help.

    George
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
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    Is there constant contact between the controller and the sub?

    For instance, if you set down or dont touch any of the control sticks, it there still a signal being sent?

    There are FAIL-SAFE circuits for RC cars, for when they are out of range of receiver the brakes are applied (Or the motor is shut off)

    I suppose you will want to give the operator a set amount of time to re-establish contact before the sub surfaces during fail-safe?
     
  3. Jure George

    Thread Starter Active Member

    Dec 28, 2008
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    Hello

    Yes there is a constant signal to the sub. If there was a loss of signal then I want the " failsafe circuit " to activate and run the pump motor for the set amount of time that the operator had preset for himself.

    I hope someone can help me with a circuit and parts list so that I can put the circuit together. I have a sub waiting for this.

    Thanks Again.

    George
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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  5. Jure George

    Thread Starter Active Member

    Dec 28, 2008
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    Hi beenthere

    Thanks for the circuit link but I don`t think it will do what I need. Also I think I forgot one operational point as well. When the submarine is " hovering" then it is motionless and no signal from the transmitter is being sent, so I guess a delay period has to be available to the operator via a variable pot control as well, I think in a few min. range should be o.k. Then if the transmitter signal is still missing then the pump motor should run either non stop OR for upto 30 sec. max. ( set by user as well ). The entire circuit then could only be reset by physically turning off/on the main sub power, either 6v upto 12v.

    Few, there is alot of things to consider here.

    Again, since I have No experience with PIC circuits or programming and I am not ready for the learning curve yet, I only want a few of these circuits for my sub fleet, regular I.C`s and Transistors etc. would be used. Look forward to seeing a circuit.

    Thanks again for Everyone`s help.

    George
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    Why don't we start by you posting the schematic diagram for your receiver?

    That way we will have something to work with.
     
  7. Jure George

    Thread Starter Active Member

    Dec 28, 2008
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    Hi SgtWookie

    Thanks for your fast Post, Please have a look at beenthere`s post, the link is there to the circuit I mentioned as possibly not doing what I need.

    Let me know what you think from the requirements I First posted at the start of this.

    If you have something, please include a circuit.

    Thank You.

    George
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    Jure George,

    You say you have a 75MHz signal, but you have not yet posted a schematic of your receiver.

    Until you post a schematic of your receiver, we won't be able to provide you with any assistance.

    We do not know how much gain your receiver has. We don't know where your receiver's AGC signal is at the moment. Once you post your receiver's schematic, it is very likely that we can find it; it is most likely in the IF section.

    Once we can figure out where your IF AGC is, we can design a circuit that will trip when the AGC exceeds the desired limit.

    Without that schematic, you would need to build another entire receiver, and then match it's characteristics to your existing receiver. This would be much more difficult to do than adding a slight modification to your existing receiver.
     
  9. Wendy

    Moderator

    Mar 24, 2008
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    Look at Wookies tag line, he pretty much speaks for all of the regulars here. We don't do tech consults via PM, but it is OK to ask for help and point to a specific thread.

    I'm not sure what you need, but a logic MOSFET is probably the best transistor. They come in some very small sizes, and handle some hefty amps. Either a CMOS 555 or a standard 555 can drive them, though for your application I'd go CMOS to maximize battery life.
     
  10. Jure George

    Thread Starter Active Member

    Dec 28, 2008
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    Hello SGTWookie and Mr. Marsden

    First SGTWookie, Sorry but I don`t have access to the Futaba receiver schematic. So I don`t know what to do now. Mr. Marsden, I was hoping one of your 555 timer circuits, modified, could serve my needs. I wish I had a schematic to the receiver circuit BUT when I researched similar fail safes, they are circuits that just plug into any receiver. Thats why I thought someone here could either show me a circuit for my needs or modify one to fill my needs.

    I hope that someone can help me.

    Thanks George
     
  11. retched

    AAC Fanatic!

    Dec 5, 2009
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  12. Markd77

    Senior Member

    Sep 7, 2009
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    If my understanding is right, the reciever stops sending pulses to control the servo when it stops recieving a signal.
    Those pulses are normally 0.9-2.14 ms long every 7.8-22.8 ms.
    I could do it easy enough with a uC but hopefully someone will come up with a way. It looks possible.
     
  13. Jure George

    Thread Starter Active Member

    Dec 28, 2008
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    Hi Retched

    Thanks for the link, its near to what I was thinking BUT I can`t adjust the time before the failsafe acts and there is no adjustment for how long the failsafe will run a pump motor. By the way, it does not say it can drive a pump motor. That is what I need it to do, run a pump motor 1A max. for upto 30 sec. max. Please look at my wish list at the beginning of my post.

    Thanks Again to All for your help so far.

    George
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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    OK, so if it stops sending servo signals if the receiver is not getting a signal, then what would be needed is a missing pulse detector, plus a 30-second timer that is triggered when a missing pulse is detected.

    What kind of power do you have available?
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    Well, see the attached. It should work on your servo power; anything from 5v to 15v; with the exception of R7 *(see the note at the bottom)

    On the left is a circle representing an input from one of your servo lines.
    If the left 555 timer doesn't get see a servo pulse after about 30mS, the timer's output goes low, which lets the right 555 timer turn on your pump for 27 seconds.

    The "pump on" time isn't exact; if you want more time on the pump motor, change R6 to 560K or 620K.

    The "missing pulse" detector timing isn't exact, either. If you want to increase the time, change C1 from 100nF (0.1uF) to 470nF or 1uF, or anywhere in between.

    If it gets the servo signal back, the 2nd timer will shut off until signal is again lost.

    * You can substitute other medium power transistors for Q3, like a TIP31 or 2N3055. You could also use a Darlington like a TIP120. If you change to a Darlington, or change your voltage supply from 6V, then R7 will need to be re-calculated.
    [eta]
    Updated attached image to show timing of events more clearly; upper plot window shows timing from timer U1, lower window shows events from timer U2.
     
    Last edited: May 22, 2010
  16. Jure George

    Thread Starter Active Member

    Dec 28, 2008
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    Hi SgtWookie

    Thank you for the circuit and info. One question, is it possible to have a variable resistor at the input of the first 555 to control how long the circuit could be off, 5 min. max. before it detects that there is No transmitter signal and then activates the Second 555? Also can there be another variable resistor on the Second 555 so that the user can set the run time of the motor, from continuously running to 30 sec. max.? Also not clear on the motor connections location?
    Thanks again for your time and help and Patience.

    George
     
  17. SgtWookie

    Expert

    Jul 17, 2007
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    I added a pot so that you can change the delay of the 1st timer.

    If you want the 2nd timer ON time to change, reduce R6 to 10k, use a 1 MEG pot between R6 and the junction of U2 Pin 2, U2 pin 6, and C2.

    Also, replace C2 with a larger capacitor. Right now, the 560k resistor and 47uF cap give about 30 seconds time on. If you simply increased the 47uF cap to 470uF, you would get about 300 seconds, or 5 minutes time delay. However, since you are replacing the 560K resistor with a 10k resistor plus a 1 MEG pot, a 470uF cap would then give you an on time range of about 5 seconds to nearly 9 minutes.

    If you want timer 2 to stay ON indefinitely once tripped, then jumper across C2 (short it to ground).

    Note that I replaced Rload with a symbol for an inductor that I named "pump". That should make it a bit more obvious where the pump gets connected. Notice that I added a diode across the pump, since it is an inductive load. If you don't use a diode there, the transistor might be destroyed when it turns off.
     
    Last edited: May 22, 2010
  18. Jure George

    Thread Starter Active Member

    Dec 28, 2008
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    To SGTWookie

    First Again, thank you for all your help. I wounder if I can push my luck and ask about a different circuit now? It`s for a submarine but in place of a rudder, the sub has Two small motors, one on each side, for steering.

    Is it possible to create a circuit that would control each motor for steering proportionately? What I mean is when Turn right is commanded by the user through the transmitter the receiver would send the signal to the circuit which would turn on the Right Side motor in the Forward rotation and the Left motor would be in the Reverse rotation, so that the sub can turn right. The circuit should also be able to control the speed of the Right turning motor, slow to fast, depending on how sharp a turn is needed. That would be the opposite operation for a Left turn as well.

    Do you think that could be done with specs as : 6v to 12v main battery, 1A max. each motor ( x 2 ), variable speed and reversible speed.

    Can this circuit be created from again basic I.C and Transistor and resistor,capacitors etc. ?

    Again a circuit included would be appreciated. Thank You.

    George
     
  19. retched

    AAC Fanatic!

    Dec 5, 2009
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    You want the same amount of power to both motors at any time, but during turns, you want the opposite motor reversed.

    That wouldn't be too difficult if it were in the original design stage. A little double pole relay that would energize during turns reversing the polarity to 1 motor. The turn control would only actually have to be a forward reverse control for 1 motor and the second would follow suit but backwards.

    With no turn controls, the relay would revert to the "all ahead" mode matching the polarities again.

    Only one speed controller would be required, feeding the relay. and 1 turn controller would energize it. (reversing the polarities of 1 motor)

    For left, the lefthand motor would spin backwards (pushing water forward) and the righthand motor would be reverse polarity through the relay thus spinning opposite the left (pushing water rear)

    Do you have the urge to revamp some of your controls? And is this what you are talking about?

    [ed]
    As for power usage, if the motors typically only run 1 at a time to turn, this addition will just about double power drain. It could be a LITTLE less the 2x because the turns would be more efficient.
    [/ed]
     
    Last edited: May 22, 2010
  20. Jure George

    Thread Starter Active Member

    Dec 28, 2008
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    Hi Retched

    Thanks for your Fast reply to my post.

    I want to explain this a little more. With a transmitter, you have 2 channells, Ch. 1 - Forward/Revers on a speed control, Ch. 2 - rudder - left/right steering with control over how far the rudder moves in each direction of turn desired, No speed control.

    So is it possible to have the Ch.2 - Rudder control control a circuit that controls 2 motors for steering proportionally with no extra speed control and have each motor behave like I described earlier ? All powered from main submarine battery 6v to 12v. Each steering motor has NO more then 1A max draw, they are Very small motors that would be used for steering and they would operate under 6v as well.

    Can a small circuit be created for my needs ?

    Thanks for Any Help.

    George
     
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