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throttle position sensor...help needed with circuit!

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  • throttle position sensor...help needed with circuit!

    Hi!,
    I'm a new member! One of your members has been highly recommended to me for his knowledge and expertise.... that was "Bushwacker", so I'm hoping that he, too, will be able to offer his help to me? This is the problem, then :-
    I have changed the throttle position sensor (TPS) on my 1991 Mercedes 190 to a type that gives a varying voltage output that is related to the throttle position. This was necessary because the car also runs on L.P.G. and the gas E.C.U. required such an input. The TPS that was replaced had simply provided a signal to the car's petrol E.C.U. to indicate the the throttle was fully closed, and another signal to indicate that the throttle was wide-open (W.O.T.). I have now lost those signals and the car would not run correctly when using petrol. So, I need to fabricate some electronics that will re-establish those signals to the car's E.C.U. The latest TPS fitted gives an output of 4.45 volts at W.O.T. and an output of 1.18 volts when the throttle is fully closed. So, what I need is a circuit / device that will transmit a 12 volt signal when 4.45 volts is detected and again a further independant 12 volt signal when the voltage from the TPS drops below, say, 1.2 volts. It would obviously be preferable if there was provision to fine-trim these two voltages to exactly correspond to throttle wide-open and fully closed. I have tried so hard to get to the bottom of this, and have posted on another electronics forum... but nobody has even read that posting, let alone replied to it! My car is at present unuseable, so any help would be so appreciated! Thanks a lot!.... David
    t

  • #2
    HI, You must be desperate to come on a toyota forum looking for help on your merc
    I'm a custard donut monster

    Comment


    • #3
      I think the easiest solution would be to replace the original TPS and get one of those 'piggy-back' type ECUs to run alongside the standard ECU but control the LPG system.

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      • #4
        yes, I am desperate! It was on recommendation that a member "Bushwhacker" would be able to help! It is not possible to fit any additional device because there is precious little space! I just need some help from an electronics aspect...... relays/triggering/circuit, etc. The guy that gave me that recommendation was an employee of "Maplins"! Hey, if you don't know how to help me yourself, I wonder if I could ask if you know someone who does? I've always done my best to help others in my past ,so thanks to you all!.... David

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        • #5
          Don't you think you would be better placed asking on a Mercedes forum or conversing with the manufacturer of the L.P.G system? Refitting the original T.P.S will 're-establish' those signals you are missing. Additional control circuitry should be used for add-ons, not the base system. You are approaching it from the completely wrong direction.

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          • #6
            If your original one provided 12v when wide open and A N Other voltage when closed (lets say 0v for argument) then what you need is a comparator.

            The circuit provides a reference voltage which will be the trigger voltage from your new sensor. You set the reference voltage at the point you wish the signal to go from low to high (and high to low, but in practice there is a little hysterysis) and bobs your uncle.

            If you power the comparator from 12v, then the output signal will naturally be 12v at wide open, and some other voltage of your choosing (probably 0v) when fully closed, with the switchover point wherever you like dependent on the reference voltage.

            I dont have the time to develop it for you, but now I've told you what you need, perhaps Soramad can build it for you.

            This is a good explanation, and the basis for what you need. The reference can be made adjustable by making R3 variable.
            Cutting steps in the roof of the world

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            • #7
              Originally posted by Apache View Post
              I dont have the time to develop it for you, but now I've told you what you need, perhaps Soramad can build it for you.
              Personally, I'd say that he'd be a fool to take this job on. This chap is triggering just about every timewaster warning in my book. From a business point of view, I personally wouldn't touch something/someone like this with a bargepole.

              I may be wrong of course, but I doubt it.

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              • #8
                That may be. I've given him the info he needs to DIY if he can wield a soldering iron - lets see if he does anything with it.

                I think you're right though. He'd be better fitting the original TPS and having the people who did the gas fit to finish the job properly.
                Cutting steps in the roof of the world

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                • #9
                  thank you for your interest.... I have a reasonable level of practical expertise and intelligence... I have designed and built my own home and converted many vehicles to run on LPG. I am keen to learn and manage to solve most problems... this one is proving a little difficult! The previously fitted T.P.S. works like this :- three wires to TPS. the "centre" wire is the +12 volts input. continuity is then made to the top positioned wire when the throttle is wide-open and a signal (+12v) and continuity is made to the lower positioned wire of the tps plug when the throttle is closed, and again a +12v signal is sent to the car's E.C.U. There is precious little space to mount another tps or detector "piggy-back" with the original tps. I will look at comparators, now, to see if they may help. I will be very grateful for an actual circuit that would do the job... i.e., a 12v signal is transmitted when a 4.45v input signal is detected, and again when a fall below 1.2 volts is detected. many thanks... DAVID

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                  • #10
                    12v at w/o and closed?

                    How does the ECU know which is which? Seems odd...

                    Anyway, look up 'window comparators' as you can design in a deadband, and just logic invert the 0v end to give you 12v out for both <1V and >4V.

                    Like I say, I dont really have the time to sort one out for you, but its really not that hard. T'internet will probably give you the bones of the design.
                    Cutting steps in the roof of the world

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                    • #11
                      I don't know anyone that works for Maplins.......do I???

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                      • #12
                        Calos!
                        Cutting steps in the roof of the world

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                        • #13
                          Guilty as charged, but what I actually said at that time was, "I don't know how to make the item you need, it is beyond my expertise" at being asked for anyone that _might_ I remembered how fantastic bushwackers technical knowlage was on all things surf and suggested the gentleman in question try asking your good self.

                          Sorry if I've caused any upset.

                          peace
                          cal
                          Bala Mud, best underseal there is, only £30 per application.


                          www.thecellardwellers.co.uk

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                          • #14
                            Bushwhacker is near impossible to upset - and I dont think anything you said would have done.

                            Think he's just jealous cos you have access to such wonderful geekery!

                            Which reminds me - you being a musician who works in an electronics parts store. You dont know where I could get a diagram of the PSU for a Behringer Eurodesk SL2442FX Pro do you - or alternatively know where I can get a replacement PSU (other than from Behringer). It's a chinese switch mode jobbie, not made by Behringer.
                            Cutting steps in the roof of the world

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                            • #15
                              Originally posted by Calos View Post
                              Guilty as charged, but what I actually said at that time was, "I don't know how to make the item you need, it is beyond my expertise" at being asked for anyone that _might_ I remembered how fantastic bushwackers technical knowlage was on all things surf and suggested the gentleman in question try asking your good self.

                              Sorry if I've caused any upset.

                              peace
                              cal
                              No upset caused, and I thank you for you're endorsement.



                              Now then, how much discount do you get??

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