May be a real stupid question...

Discussion in 'General Electronics Chat' started by trs300, May 22, 2010.

  1. trs300

    Thread Starter New Member

    May 22, 2010
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    Hi all, I'm very ignorant when it comes to electronics so I'm looking for help to answer questions when I run into them...

    I'm putting together a controlling device that uses a 5V 250ma pressure as the control voltage supply. I want to be able to adjust this supply to a 0v to 5v variable pressure using a pot (like a dimmer). How do I put that together? pot & resisters? How do I size them and how would they fit up?

    Thank you

    Tim
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    A potentiometer would do it, but the voltage wouldn't be that stable, not at a ¼A. The term is voltage and current, not pressure, that doesn't apply in electronics as you use the term.

    What are you planing on using this voltage on? It would help to know that.

    Making a variable voltage that is pretty stable isn't too hard, but having it powered by 5V and outputting the entire 0-5V range is almost impossible (unless you don't need the ¼A current). Can you live with 0-4.2V output?
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    Not a stupid question at all.

    It would really help a great deal if you could explain more about your application.

    Can you post a circuit, or a datasheet/manual for the part or circuit that you wish to control?

    PWM might be what you need. With PWM, the output is switched on and off rapidly, but the width of the pulse is changed. You can get from around 2% PWM to around 99% PWM using a simple 555 timer IC and some supporting components, like a timing capacitor, a fixed resistor, a pot, a diode, and a semiconductor switch (transistor or Darlington) for the high-current output.

    However, the nature of your load will dictate what kind of circuit you actually need.
     
  4. guru200773

    Member

    Apr 26, 2010
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    In this world no question is a stupid question.. So ask questions what ever may be it is but related to electrical and electronics... The experts in these forum are always ready to help u :):)....
     
  5. trs300

    Thread Starter New Member

    May 22, 2010
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    Thanks for the responses and the kind support. I figured out why my pot was not working... I was not connecting the other side to ground. I need to get I the mind set that we are often moving current from one place to another, and not simply shutting down the flow like a water faucet...

    The application is a PWM controller board. I did not build it, but I'm adapting it for a purpose I have... Most of my challenge will be on the 5v control voltage side. and as I said, this is a 5v 250ma supply.

    Normal use of the board is you would route this 5v supply out to some sensor designed to provide feedback in the 0v to 5v range. The feedback v is feed into the controller which then manipulates a PWM voltage signal out to the solenoid valves. The final output is a variable PWM, 0v to 15v at 4 amps max.

    I have a sensor in this control loop designed for a purpose and works just like it should... It reads pressure at from 0 to 100 kpa and converts that vacuum reading to a 0 to 5v return signal..




    Now this is where it gets tricky... I need to do the following...
    • 1.) Introduce a Gain in the sensors return signal so that I can deliver max output to the solenoids sooner... In other words, amplify the control signal coming back from the sensor by up to 2x. This needs to be on a pot so that I can ramp it up, or back down to normal.
    • 2.) Introduce a "Base signal", or floor voltage. When the sensor says... "Give me nothing..." (0v), I need to be able to hold the output at a given voltage... And I need to be able to control this by a pot also...
    So I have a control signal coming back from a sensor I want to be able to multiply via knob, plus I want to come in from another direction (source) with a "Minumum" control signal voltage to act as a floor...

    I'm getting there. Gotta run and get some diodes. these two pots ans the sensor are fighting with one another at the moment lol... Gotta make it so that ones signal cannot back up ino the other...

    --
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Can you make a drawing (sketch) how you connected the parts?
    Is there also detailed information on the PWM board?

    Can you describe (perhaps a table) at what pressure you want wich voltage?

    Bertus
     
  7. trs300

    Thread Starter New Member

    May 22, 2010
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    Here is what I'm trying to do... I hope this makes sense. I know it's not aq real schematic. It more represents the operation and limits... I have never put something like this tegether, so it's coming together very slowly..

    [​IMG]
     
  8. trs300

    Thread Starter New Member

    May 22, 2010
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    Well... my op apmp circut is not working... Here is what I put together followed by the instructions I was given. Can anyone see anything wrong?

    Thank you.

    [​IMG]


    [​IMG]
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    Well, it appears that you are attempting to modify the inputs to an automotive ECU.

    This is basically tampering with the emissions controls, and is not legal here in the States, nor in most other countries.

    Your idea would cause the engine to run very rich when in open-loop mode, and would result in a "check engine" light in closed loop mode. You would receive poor fuel economy and would have very high emissions. It is likely that you would have accelerated engine wear due to the excess fuel washing engine oil from the cylinder walls. The large amount of unburned hydrocarbons would be likely to cause failure of the catalytic converter, if not immediately resulting in a fire, or at least backfiring in the exhaust.

    I don't know why people think they have to make changes to their engine controls. It's illegal, and results in poor fuel economy, high emissions and short engine life.
     
  10. trs300

    Thread Starter New Member

    May 22, 2010
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    LOOK... First off. I appreciate the advice on the circuit questions. I do not need a lecture on what this, if applied to the ECU of an automobile, would do. I NEVER EVER said this was going to be used that way. Just because I'm using an automobile MAP sensor to convert a Vacuum pressure into a control signal does not = (Me messing with the ECU in my car)...

    So to be VERY CLEAR... THIS IS NOT BEING USED ON AN ENGINE... Okay?

    Sorry you felt the need to lecture instead of help. I'll figure out the issue with the op amp some other way, thank you.


    -----------


    Now, being more productive... I noticed that the op amp had no feedback loop. in place of R29 I put a 4.7K resistor from the outlet back to the signal input. I was expecting to see a 4.7 time gain... But no luck.

    In actual operation, the voltage from the op amp is like this...

    Vout = (Vsupply - Vsignal) or... Vout = (Constant 5v to pin4 - Variable MAP Signal in)

    Vout = (5v - 4.9v) = 0.1v
    Vout = (5v - 4v) = 1v
    Vout = (5v - 3v) = 2v
    Vout = (5v - 2v) = 3v
    Vout = (5v - 1v) = 4v
    Vout = (5v - 0.3v) = 4.7v

    ---


    I think I need to start over... I just need a simple op amp that will do the following...
    1. at zero gain, will not amplify the map signal at all, but will simlpy pass it through.
    2. at full gain, will have amplified the MAP signal voltage to where I get full 5v output at ~ 2.2v of MAP signal in...
    3. The amplified signal will never exceed 5V
     
    Last edited: May 23, 2010
  11. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
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    Whoa friend, the 'lecture' is a good thing. This thread will be around forever. some 16 year old kid is going to google 'MAP sensor circuit' and this will come up. prior to Sgt.Wookies 'lecture' that kid likely had no idea what it could do to an engine, now he does.

    He was the 2nd person to reply to your thread. He is here to help. STANDARD safety disclaimers will be added. Im sure it was nothing against you as a person / designer / mechanic.

    So, if not an engine? What is the end result of this device?
     
  12. trs300

    Thread Starter New Member

    May 22, 2010
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    Agreed... I think a simple... "I hope your not going to use this on an ECU as it will damge the engine based on this design..." would have been enough. The whole, "It appaears as if you are going to..." and "Don't know why people do..." was based on assumptions.

    Anyway... The controllers output will be manipulating PWM supply voltage to two PWM driven solenoid valves used to control pressure in a fluid system.

    --
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    Playing the "Mr. Nasty" card will get you nowhere.

    We've had plenty of people try to implement what I will call "ill-advised" circuits on their vehicles. But basically, they were stupid and illegal circuits that would burn up their engines right after destroying the planet.

    So alleviate our fears.

    Why don't you explain what you really are attempting to do, and we will try to help you with it.

    I'm really an obliging type. Just don't try to do something that IS stupid, like modifying automotive engine controls. Those types of things really are far beyond most "shade-tree" mechanics.
     
  14. trs300

    Thread Starter New Member

    May 22, 2010
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    I may have been a bit over-reactive. Sorry. I'd been banging my head on a wall all weekend and had gotten nowhere...

    Can we wipe the slate and start again?

    Let me try and explain what's going on and what I'm trying to do. If I had done that right away we would have not got tangled up to begin with...

    ----

    I have a car and I'm part of a community for these these cars. The transmission on this car shifts somewhat soft for most peoples taste (mine included). Another forum member created a device the has a knob with settings 0-6. This knob controls shift firmness. 0=stock <> 6=VERY FIRM.

    The device hooks onto three wires of the TCM (transmission controller) and apperars to be supplimenting the PWM signal to the Line pressure and Modulation valves in the transmission producing the shift firmness increases.

    The problem is the device does not know about engine load. So if you crank the firmness setting up to 6 (max), at wide open throttle (WOT) you get a nice firm shift. But at that setting, as you coast down or you accelerate at lower partial throttle, the shifts are harsh and "Bang" into gear bacause the trans pressures are to high for those conditions. If you turn the knob down to 3, the shifts are good at midrange, still bang a bit at low range, and is a bit soft at WOT...

    What I thought was, wouldn't it be nice to introduce the engine load into this control scheme, set the device at 6 and then ramp down it's effect as engine load aproaches minimum (idle).

    I do not know how this device works, nor will I attempt to open it up and look at what's inside. I think that crosses my moral boundry as this person put a lot of work into this solution...







    I do Think / know...
    • If you pull the power lead to the device it will simply act like stock
    • It's effective power control range is from 9 to 14 V
    • I know the two valves are PWM controlled
    • I think the valves operate between ~ .1 to 1.1 amps
    • I think if I cut back on the supply power to the device, from 14V to 11v lets say, the the effect it as on shift pressure would be deminished (I have not tested this yet)
    ----


    I've thought about a few solutions to this...
    1. Try and build a completly new device with engine load integrated (but I do not understand how to do this)
    2. Use engine load to regulate the power supplied to the shift device
    3. Use a custom switch box... See below. *leaning this way...
    --Custom switch box---
    1. Tap into engine load signal, or throttle position signal.
    2. Operate 6 relays based on input signal. Each relay would be designed to close it a given % of engine load or throttle position.
      • Relay1 = 0-10%,
      • Relay2 = 10-20%,
      • Relay3 = 20-40%,
      • Relay4 = 40-60%,
      • Relay5 = 60-80%
      • Relay6 = 80-100%
    3. Each relay would close circuit where the user (using a 6 position slider switch), would select a "knob position". This would allow the user to custom tune the effect from the shift enhancer and it would be tied into engine load... The end result might look like this...
      • Relay1 = 0-10% = Setting 2
      • Relay2 = 10-20% = Setting 3
      • Relay3 = 20-40% = Setting 3
      • Relay4 = 40-60% = Setting 4
      • Relay5 = 60-80% = Setting 5
      • Relay6 = 80-100% = Setting 6
    To install the shift enhancer custom controller you would only need to cut one, and tap another, of the 6 cluster wire lead going to the knob, install some plugs, and plug the controller in between the the two...

    We would take over knob position 2 (which is almost no change) and have it be the active position for the controller... Any other knob position would simply work the same as it does now...




    So in the end it would be like this...
      • Knob Setting 1 = Off (stock) (by original design)
      • Knob Setting 2 = Custom controller settings using engine load.
      • Knob Setting 3 = Firmer (by original design)
      • Knob Setting 4 = Firmer (by original design)
      • Knob Setting 5 = Firmer (by original design)
      • Knob Setting 6 = Firmer (by original design)
    Hope this makes sense...


    ---
     
    Last edited: May 24, 2010
  15. SgtWookie

    Expert

    Jul 17, 2007
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    Seems like you could use engine manifold pressure alone to determine what kind of shift you'd need.

    If the pressure is very high (near atmospheric), you're running near WOT, and you would want really snappy shifts.
    If the pressure is very low (high vacuum) you are running closed throttle, so you would want very smooth shifts.

    If you were accelerating under light throttle, the manifold pressure will drop as the engine "catches up" with the throttle position setting.

    I don't see that there is a need to look at the throttle position. Attempting to read the TPS sensor's voltage brings up safety issues; if a circuit that you built failed in a bad way, and your ECU received a signal that the TPS was wide open, it might lead to your engine running at WOT, which has proven fatal in a number of Toyota incidents.

    What you might want is some control over how much effect the MAP sensor has over the shift firmness.

    In GM transmissions of old, there was a vacuum modulator in the transmission body; it did exactly what you're looking to do. Very firm shifts at WOT, and very smooth shifts at light throttle.
     
  16. trs300

    Thread Starter New Member

    May 22, 2010
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    I agree with everything you've said. That is the reason why I was going to simply get a map sensor, feed it a supply voltage, read and respond to the return signal. I was not even going to use the map in the car. I was going to get one and dedicate it to this service...

    Now all that said, it's not as easy to manipulate the TCM as it sounds. The shift logic tables are completely controlled by the PCM and TCM. Shift points and torgue management are all locked up on the computers. And if you try and feed current directly to the PWM vlaves in the transmission the car goes into "Limp Mode". I believe the "Firmness Box" developed by this other guy is enhancing the PWM signal to the line pressure valves in a way that it does not make the computer think something is wrong. Maybe he's manipulating the duty cycle or something... I don't know. What I want to do is lay some control logic tied to engine load over the top of his controller...

    One way is to regulate power to the sift enhancer

    The other way is to build this "Switching Box"...

    How difficult is it to control a series of relays (having each one close over a specific voltage range from a sensor?)


    For example...
    • 0-1v (Relay1 closed, all other open)
    • 1.1-2v (Relay2 closed, all other open)
    • 2.1-3v (Relay1 closed, all other open)
    • 3.1-4v (Relay1 closed, all other open)
    • 4.1-5v (Relay1 closed, all other open)
    ---
     
  17. SgtWookie

    Expert

    Jul 17, 2007
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    You want a 5-stage window comparator.

    See the attached.
     
  18. trs300

    Thread Starter New Member

    May 22, 2010
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    Thanks for the tip.

    Would this work if the control signal was 0 to 12 volts?
    And is this a "Thing" you can buy, or do you need to assemble one?

    I'm looking to find something as much "pre-assembled" as possible...

    I found that if you route a 14 supply to the map sensor (normal voltage with car running) it works just fine. At idle it put out around 2.8v and at WOT it's around 12.5v...

    Attached is an example of what I'm trying to put together. on the right side of the screen is new... The "Shift Enhancer Box & Rotating Selector Knob" is existing...
     
    Last edited: May 24, 2010
  19. SgtWookie

    Expert

    Jul 17, 2007
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    You could probably use an LM3914. That IC has 10 window comparators in it. It's primary use is for an LED display driver.

    If you try to run the MAP sensor for very long straight from your vehicle's electrical system, it will soon be dead.

    [eta]
    While you might think that you will get a fairly constant 13v-14.5v from your vehicle's electrical system, you can get very large "transient" voltages; spikes up to 60v or even more. A brief blast like that will wipe out even fairly robust circuits.

    Automotive environments are among the harshest on the planet; temps range from -40 to 125°C, fluids (some corrosive), vibration, electrical noise - it's a nightmare. If you don't plan for such things, you will wind up with a smoking pile of junk in short order.
     
    Last edited: May 25, 2010
  20. trs300

    Thread Starter New Member

    May 22, 2010
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    I'll read up in the LM3914. Thanks. As for the voltage, I was planning to bring it down to a 10v supply to the map sensor using a regulator and put a resistor to control current.

    I'm actually taking time to read up on things... Believe it or not I never really knew what a transister did... I read up on them yesterday (Zener diodes too) and I was like "WOW! That's cool stuff!" I'm going to be playing around with these things and try and get my knowledge base up a little bit before I try and put something together...

    >>>>>>>Update....

    I think this is going to work perfect! Thanks!

    --
     
    Last edited: May 25, 2010
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