Peizo Balancer Project-Need Help

Discussion in 'The Projects Forum' started by nissan20det, Jul 29, 2015.

  1. nissan20det

    Thread Starter New Member

    Apr 3, 2015
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    Hey guys!

    So Ill try to keep this as simple as possible. I am recreating a turbo balancer i found on the web. I am not very educated with electronics, all self taught, but I do know a bit. This project includes two Piezo transducers in a push pull configuration connected by a rod with the rotational mass centered between the two, the rod will rock left and right de-pressing off one Peizo as it presses on the other. The idea is to make an led light as the rotational force point towards one Peizo. I think what this guys is doing is adding the de-pressed signal to the pressed signal in one direction and subtracting in the other to cancel itself out. Now the Led part of this I will leave out as I understand it, and have no problems. It is just a comparator with a variable voltage source to adjust sensitivity of the led blink. The inverting input of the comparator is connected to a variable voltage source while the non-inverting is fed with the output of the transducer circuitry. This circuit is based on a +9 -9 GND supply.

    I cant figure out what I am doing wrong because I'm not sure what this circuit is doing. This is where hopefully you guys can help. I attached a picture of the Piezo circuit. Their are two of these one for left side, one for right. They are connected as: output 1 from one side will go to input 2 or 3 on the other depending if you have same or opposite polarity Piezos.
    Buffer-schematic.jpg
    This Is was I think I know:
    The Piezos are 3 wire, that I currently have -9 +9 wired to black and red and blue is my output. That output will swing Pos and Neg I think. So lets say my a pulse is positive on one said side. After IC1A my pulse is still positive at ICpin1. Then the Neg feedback loop will stabilize the output from swinging way high, as well keep ICpin1 close to the input at ICpin3. That Pos sig now reaches ICpin6 and will now be inverted to a neg pulse. (Now a Neg pulse out Makes me mind boggled how a feedback loop would help if the inverting input(pin6) in Pos and output is neg???). Now the output of IC1B Pin7 is fed to the other side of the balancer. Now Im not sure the difference here between: Output of IC1B Going to input 2 or 3 on the other side. So say my neg pulse is fed to input 2 IC2A pin 2/1. That neg pulse will then make the 2nd Piezos pulse into pin3 Twice as large at pin 1 right?(It will add the two) Then inverting that pulse to neg after IC2b.

    If I input the start sides pulse into IN3 wouldnt that do the same thing right. pin6 would be the same size pulse pos as the input neg going to pin 5 there for adding them right?(Ex. -0.4v going to pin5 as a +0.4v goes to pin6 the output would be the same as a -0.4 going to pin2 as a +0.4 goes to pin3) I see how there adding but not canceling each other out the other way. Maybe one of you could explain this circuit to me.... Im also confused on inverting. If you send a Neg pulse to the inverting input as the non inverting is tide to ground what does that do? give you a pos out?

    If this is to big of a pain to figure out then could someone help me work up a simple circuit that will add one direction and subtract(or do nothing) the other way. accurately

    Thank you for any response, means alot!
     
  2. ScottWang

    Moderator

    Aug 23, 2012
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    Where is another circuit that it was connected to K2 connector?
     
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Can you post a pin-out/datasheet of the piezo? Why not use a simple 2-pin piezo?
    Are you using a matched pair of piezos with identical sensitivities?
     
  4. nissan20det

    Thread Starter New Member

    Apr 3, 2015
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    http://www.digikey.com/product-detail/en/0/102-1130-ND

    This is the piezo, and yes I was trying to get one that matched the on used buy the designer. He used this one from the uk
    http://www.produktinfo.conrad.com/d...0-da-01-en-PIEZOKERAMISCHER_SCHALLWANDLER.pdf

    The circuit for piezo K2 is the same as K1.... circuit with K1 will have input 2 and 3 open as well and circuit with K2 will have just pin 2 or 3 open depending on piezo polarity. output 1 K1 goes to K2's input 2 or 3 K2's output goes to Comp.
     
  5. nissan20det

    Thread Starter New Member

    Apr 3, 2015
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    Excuse my grammar on the last post. I was in a rush and did not read it over, My apologies.
     
  6. nissan20det

    Thread Starter New Member

    Apr 3, 2015
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    Okay I'm kinda repeating what I said about my last confusion of the K2's 2nd or 3rd input. but I think I got it!

    ( Rotational mass going left towards K1) Out of the First Piezo circuit K1, Say I have a positive +0.5v pulse that will stay positive after IC1A and would invert after IC1B that output going into K2's input "2" (Inverted now so -0.5v) K1's -0.5v output will cancel out K2's -0.5v output at IC2A. Now giving me a 0v then nothing at IC2B with a end result of 0v.

    Now the opposite ( Rotational mass going towards K2) K1 is now -0.5, a neg into the Non-inverting would invert to +0.5 at IC1A and would Re-invert at IC2B, Back to a -0.5v as it goes to K2's input "2" again, meeting K2's output of +0.5v at IC2A and will add to a output of +1.0v then inverting to -1.0v at IC2B.

    (Mass still towards K2) Now If I send K1's Output into K2's input "3" instead of "2", K2's Output of +0.5v will stay the same after IC2A and at IC2B will add to K1's circuit output of -0.5v as well as inverting to a +1.0!
    (Mass going left would still be 0v)


    Is this right?
    Sorry if its hard to follow. It seems he set up a logic network with opamps to be able to work with a less then 5v signal. However if this is right then Im stuck why this isnt working. I have my circuit the exact same...even part numbers... but I seem so get a good strobe like stand still at times but if I stop and spin up again, I cant seem to get the Strobe timing mark to stay in the same position...

    This will help clear things up. Here is the project
    http://www.technologie-entwicklung.de/Gasturbines/Balancing_Tool/balancing_tool.html

    Thanks!
     
  7. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    This is the intended setup as I understand it :-

    Balancer.gif
    Simulation shows it works fine. Depending on the position of the selector switch you get either addition or subtraction of the two piezo signals (depending on their individual polarization). It's subtraction that you need. From the datasheet for the piezos it looks as though you should not be using the blue wire: just connect black to ground and red to the opamp non-inverting input. Instead of using a selector switch you could simply swap the red and black wires of one of the piezos.
     
  8. nissan20det

    Thread Starter New Member

    Apr 3, 2015
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    Well thats good! Okay so what I tried is to plug the black wire on each piezo to ground and red to non-inverting input like you said, it acts the exact same.
    Trigger-Schematic.jpg
    Now the second half of this schematic "Trigger" shows common emitter on T1.( the lower half is a PWM motor controller that I did not do, I'm currently using an Arduino with an Adafruit V2.3 motor controller). Instead of using a lmc662 for the trigger, I'm using a single channel off a LM324 comparator. Now if I connect T1 emitter to GND I get no blink(still no blink when piezo blue left open), If I connect emitter to Neg (how it is now) It blinks and works, not very consistent, and doesn't quite work like the designer explains. Is the trigger maybe where my problem exists?

    Mine is set up just like his but with the LM324

    And im not sure what you mean by a selector switch? Is that just referring to the simulation? And in the schematic you drew looks confusing... that selector switch is throwing me off... Depending on the piezo's polarization(positive flexing both ways or pos one way and neg the other) you plug the output of the first buffer into "IN 2 or 3". It looks as if your switching which input based on polarity, the output from one is plugged into 2 or 3 permanently and does not change. he just set up the other pin incase you have "same polarity piezos". I think that's what he's doing anyway maybe that's where I'm wrong, am I suppose to have a switch somewhere? He doesn't explain you need something to switch what input to go in based on what direction the mass is going.

    This is the interconnection diagram
    09-BALANCER-connect.jpg

    Thanks
     
    Last edited: Jul 30, 2015
  9. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Good.
    Are you using GND or -9V as the negative power supply rail for your LM324?
    What is the voltage of the positive supply for the LM324?
    In the sim I show a switch which serves the same function as the AB selection arrangement in your interconnection diagram above.
     
    Last edited: Jul 31, 2015
  10. nissan20det

    Thread Starter New Member

    Apr 3, 2015
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    Why is that good?

    I am powering my system with ATM with +3.31 and -3.15 I had it at +9-9 previously. I changed for simplicity, I have the 3v symmetrical power supply made.... The LM324 is powered +3.31 -3.15. I was worried 3.3 was to low altho the Texas Ins. data sheet did say 2-32v.

    Okay that's what I figured.
     
  11. Alec_t

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    The blue wire on the piezo in the datasheet connects to a smaller patch of the piezo material than the red wire does. I was concerned that use of the smaller patch might make matching of the two transducers less likely. But if you get the same result then clearly any mismatching is not an issue.
     
    Last edited: Aug 1, 2015
  12. nissan20det

    Thread Starter New Member

    Apr 3, 2015
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    Okay cool!....

    What I told you I was using I mixed up. Im actually using a LM339 comparator. I mixed up the LM324 op amp and 339 my bad.... At the moment Im trying a 324 tho
     
  13. nissan20det

    Thread Starter New Member

    Apr 3, 2015
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    Okay I just tried the LM324. After i hooked it up the led stayed on all the time. so I switched the Emitter on T1 back to GND like the schematic said instead of Neg and it works like that now. As well its a little more consistent. The problem Im having now which is my inconsistency is as I speed it up I can see my timing mark spin like a clock. (I get a good stand still of the timing mark if I stay at a said speed, As I increase speed the mark will rotate.) Why does it do this? How do I know what speed is right? Is there a way to keep it in the same position at any speed? I thought that was the whole point.
     
  14. Alec_t

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    I'm having to guess what your setup is, but it seems to me that, like any stroboscope, if the circuit operation isn't synchronised exactly with the object rotation speed the timing mark will appear to drift. I think the original article referred to using low speed for the balancing?
     
  15. nissan20det

    Thread Starter New Member

    Apr 3, 2015
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    Sorry for the delay... I'll post some pic's of my setup tomorrow .

    I think I found a couple potential problems, Let me know what you think. I have a lot of noise or some artifacts I don't want. Do you think one problem could be the contact from transfer rod to piezo? Just like the creators setup, instead of the carbon rod I have a Stainless 3/16 brake line tube as the rod(Pinned in center). I'm wondering if the signal would differ depending on how much surface area of the rod contacts each piezo. Say one side has the full 3/16 wide tube is flush against the piezo and the other has maybe 85% contacting, would that affect the subtraction/addition signal? Maybe be to small or to large? Should I blunt point the ends of the rod to be equal?

    Also the brass flex plate he uses on the moving "Y", He doesn't say a thickness. I am right now using a .020 spring steel filler gauge. I'm wanting to know if that thickness/give of that will affect this. Should I go thinner, thicker?

    Lastly I realized the led will blink on rebound... So say mass going left, left peizo positive, right Neg, as left rebounds it goes neg but as right rebounds it goes Pos and blinks the led. Same thing in reverse for opposite movement in mass. Is there an easy way to remove this, or work around?

    Maybe this Idea; What do you think about setting this up with an optocoupler/receiver (Reflective material) on the back of the compressor wheel face to count Millis per rev. Then calculate (so say I'm at 100Ms per rev, I set a de-bounce time, 20% of RPMilli. So 20% of 100 would give me 20. I set it up where that debounce timer starts once the threshold (I manually set with a Pot) is exceeded. and only take a reading for 20Ms out of the 100Ms revolution. I would make the percentage adjustable on the fly with a pot 5-40% to start. What do you guys think? Any other benefit to a rpm counter? I Have the parts on hand to try this. I was also thinking should I just order a magnetic 500+ rotary encoder? Then I could find the exact spot..... that maybe down the road but non of this helps my trigger its self. Im not getting a solid blink per rev, Its all over the place. So another question would a microprocessor doing the math and trigger portion be a better route\more accurate? I plan to do this with an arduino,
     
  16. Alec_t

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    Sorry, can't advise on the mechanical stuff. I'm a circuit man.
     
  17. nissan20det

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    Apr 3, 2015
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    How about this idea?

    And I have a question... If a set a comparator up with a piezo strait to the non inverting side, then have a variable voltage -3 to +3 on the inverting input. I get a negative output?? If i switch the inputs around I get nothing on a LM393QT and the LM339 I get neg no matter how the inputs are.. Why? As well on the 339 If I adjust the threshold above 0.6V the output goes high and if I adjust below -0.6 it also goes high. Why is this? and the LM393 does this as well but only below -0.6 anything above it acts normal. This is Powered GND +3... Id I power -3 +3 the led doesnt go high no matter where I set the threshold as it should but I cant get the piezo to make the output go high no matter where i set the threshold. Whats the deal here?
     
  18. Alec_t

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    Please post the exact circuit, showing all connections to the comparator.
     
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