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  • #16
    Originally posted by KLZE Porsche View Post
    Good idea that I hadn't thought about. Most cars use PCM for the cruise that is derrived from the sine out-put of the VSS. Good thinking because I will bet that there is a PCM output on this car from the ECU to the cruise control.
    What is it that you are working on?? Usually the PCM doesn't output a digital VSS signal for cruise control. Usually it comes from the ABS module or the Gauge cluster.

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    • #17
      You could just use a diode and DC solid state relay to convert the AC waveform into a ground pulse signal. Many have a 3-32V DC input (wide enough to cover your VSS voltage) and tons of switching current, they are also fast enough to switch your device easily (by my calcs 200mph = 222.22hz).
      Supercharged - 94' PGT: ZE, MS2, W/M Injection, weight reduced, manual steering because weekend race car! mods and pics thread
      Turbocharged - 06' WRX: 3" exh, ECUTEK ROM, MRT intercooler, VF34 pic
      Nitrous Oxide - 79' Yamaha QT50 'Yamahopper' 70cc, MLM pipe, VM18 carb, dual stage reeds etc. pic

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      • #18
        Originally posted by stoker100 View Post
        You could just use a diode and DC solid state relay to convert the AC waveform into a ground pulse signal. Many have a 3-32V DC input (wide enough to cover your VSS voltage) and tons of switching current, they are also fast enough to switch your device easily (by my calcs 200mph = 222.22hz).
        I have some Crydom DC/DC SSR's but they are rather bulky and a bit too expensive to be using for this. I have seen a few smaller SSR's -but most all of them are DC/AC.

        Do you know if you can put DC across the switched AC terminals of a SSR? The signal being turned on and off by the relay is likely a 5VDC ref signal generated internally by the cluster since it is un-likely that it would be an AC ref.

        ---------- Post added at 12:18 PM ---------- Previous post was at 12:14 PM ----------

        Originally posted by crazycanadian View Post
        What is it that you are working on?? Usually the PCM doesn't output a digital VSS signal for cruise control. Usually it comes from the ABS module or the Gauge cluster.
        It is my SC400 and I am putting a 1990 Olds Cutlass Supreme cluster into it. The cluster is looking for a 4000 PPM switched ground for it's own internal ref voltage and the SC400 VSS is an active sender with a sine output. I believe the PCM (ECU) in the SC400 conditions the VSS signal into a PWM output for the cruise control module.
        Success is a measure of determination!
        Bonneville Dreamer-(AKA Purple Pimp Mobile)
        $500 Gas-Electric-Gas Reconversion/Restoration
        Mini-me & 500k "Old Gal" RIP
        Restoration of a legend

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        • #19
          Originally posted by KLZE Porsche View Post
          Do you know if you can put DC across the switched AC terminals of a SSR? The signal being turned on and off by the relay is likely a 5VDC ref signal generated internally by the cluster since it is un-likely that it would be an AC ref.
          Not into the input of the SCR but into the output should be fine depending on the internal design, give me a part number and ill look it up. Something like a SY4090 should do the trick if your happy with a PCB mount component.
          Supercharged - 94' PGT: ZE, MS2, W/M Injection, weight reduced, manual steering because weekend race car! mods and pics thread
          Turbocharged - 06' WRX: 3" exh, ECUTEK ROM, MRT intercooler, VF34 pic
          Nitrous Oxide - 79' Yamaha QT50 'Yamahopper' 70cc, MLM pipe, VM18 carb, dual stage reeds etc. pic

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          • #20
            Originally posted by stoker100 View Post
            Not into the input of the SCR but into the output should be fine depending on the internal design, give me a part number and ill look it up. Something like a SY4090 should do the trick if your happy with a PCB mount component.
            Actually -the more I look at the Olds diagrams -the more and more it looks to me that the ECU shunts the incoming VSS signal to ground and the cluster sees it as a voltage drop. I think I may have to buy an Olds VSS sender and hook it up/spin it to see what kind of output it has. This is too much for my brain and I think I am going to fry a diode or something.

            Damn I would hate to have to buy an Olds ECU and rig it up under the dash as a tach/speedo signal conditioner. That is a big-ass conditioner! Maybe I will post up some diagrams and whoever can look at them and see what is going on in the circuit and what is needed for the conversion wins!
            Last edited by KLZE Porsche; November 22, 2014, 07:32 AM.
            Success is a measure of determination!
            Bonneville Dreamer-(AKA Purple Pimp Mobile)
            $500 Gas-Electric-Gas Reconversion/Restoration
            Mini-me & 500k "Old Gal" RIP
            Restoration of a legend

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            • #21
              Originally posted by KLZE Porsche View Post
              Actually -the more I look at the Olds diagrams -the more and more it looks to me that the ECU shunts the incoming VSS signal to ground and the cluster sees it as a voltage drop. I think I may have to buy an Olds VSS sender and hook it up/spin it to see what kind of output it has. This is too much for my brain and I think I am going to fry a diode or something.

              Damn I would hate to have to buy an Olds ECU and rig it up under the dash as a tach/speedo signal conditioner. That is a big-ass conditioner! Maybe I will post up some diagrams and whoever can look at them and see what is going on in the circuit and what is needed for the conversion wins!
              Hi Mike,
              It is easy to convert the sine wave to a square wave.
              The cheapest way is to build a simple circuit board using strip board.
              If keeping cost down, this is the best way.
              the idea of using a schmitt trigger is good, by using an op amp, by setting the differential input at a certain level by resistors, the output can feed into an opto darligton coupler NPN, with the emitter to ground.
              This will give your isolated ground pulse.
              Frequency in from your VSS will be the same frequency out.
              You will have to first, find what frequency the VSS is giving out in relation to your vehicle speed.
              If the VSS frequency is higher than the 4000 pulses/mile, then you can use a 4017 decade counter in-between the trigger op-amp and the opto-coupler to give you scaling, with selecting any one of the 1-10 outputs to feed the opto-coupler (and reset on the 4017) and the trigger op-amp output to the clock input of the 4017.

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              • #22
                Originally posted by KLZE Porsche View Post
                I am in the middle of another digital dash conversion and I have run into a problem with a speedo VSS incompatibility. I have a digital dash that requires 4000 pulses per mile of ground/no ground. The car vss sender is a powered one that outputs a sine signal of unknown amplitude.

                How can I make a simple circuit that will turn this sine signal into a ground pulse signal? The pulses per mile are an exact match -so all I have to do is to convert the signal. Since I do not know the exact sine signal output amplitude -it would be nice to have a circuit that doesn't really care if it is 5v or 12v sine.

                Please help me with this simple signal converter. Thanks!
                Hi Mike,
                Sorry, I didn't read this bit.
                Just an op-amp with the -ve input between 2 resistors or pot to give your threshold voltage and + ve input to the VSS.
                the output to drive a darlington NPN transistor via a resistor (emitter to ground, and possibly a 10K resistor from collector to +ve supply)
                The collector terminal to your dash.
                This will give your square wave ground pulse.

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