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Frequency increase

  1. Nov 25, 2009 #1
    I have a frequency from a sensor in my truck that it 2.5 volts constant and the frequency varies depending on the amount of pressure that the sensor recieves. is there a way that i can manually change the frequency of the signal that the sensor puts out? i want to be able to increase the frequency.
     
  2. jcsd
  3. Nov 25, 2009 #2

    f95toli

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    There are certainly methods that can be used to increase the frequency.

    But in order to answer your question I think we need some more info.
    What is the frequency range?
    And how much do you want to increase the frequency?
     
  4. Nov 25, 2009 #3
    The simplest way is to use an exclusive OR or NOR gate. Use an RC circuit to delay one input with respect to the other. This will double the number of pulses.
    Bob S
     
  5. Nov 25, 2009 #4
    the frequency range is from 100-130 hertz. i would like to make the frequency go up to 180 hertz which would be a 50 hertz increase. if you need more info let me know.
     
  6. Nov 25, 2009 #5

    berkeman

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    I think we should ask for more info. Messing with sensors in your vehicle can be a bit dangerous, and mildly illegal (emissions changes, etc.).

    What pressure sensor are you referring to? What does it do? Why do you want to make its output go higher than stock?
     
  7. Nov 25, 2009 #6
    could you give me a picture of the schematic that i would need for the OR or NOR gate circuit and will i be able to control how much the frequency would be increased kind of like you would control voltage with a variable resistor or would i only be able to double the frequency that is input. there is minimal risk for damage to the electrical system it is able to handle a 256 hertz signal before damage is a concern and i only want 180 hertz. emissions are not a problem, the sensor is a boost sensor and limits the amount of fuel during low rpm until the turbo boost is raised all i want to do is make the engine think that it has more boost before it actually does to get a little more power during take off. it is in a 96 powerstroke diesel and way out of warranty.
     
  8. Nov 25, 2009 #7

    berkeman

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    The XOR circuit is a frequency doubler, which doesn't sound like what you need. Could you do a quick plot of output frequency versus input frequency and post it? Do you want a constant frequency multiplication (like 1.38 = 180/130), or a constant frequency offset of +50 Hz (= 180-130), or something inbetween?
     
  9. Nov 25, 2009 #8
    the actual working of this sensor is something that i do not know. what i do know is that there are 3 wires one is a 5 volt reference wire, the 2nd is a sensor ground that is just a safety, the 3rd is the signal wire. i have hooked up a digital multimeter to the reference and signal wires. the reference inputs a constant 5 volts +/- .1 volts and the signal puts out about 2.5-3.5 volts. the 5 volt reference wire does not have any frequency to it according to my multimeter. when the truck is at idle the signal wire puts out 2.5 volts and 107 hertz. i know that at 20 psi of boost from the turbo the sensor increases the hertz to 165 according to the sensor specs that i found. what i would like to be able to do is control the hertz (like you would voltage with a variable resistor) if that it not possible then the XOR circuit would also work since it will double the frequency and therefore trick my engine's PCM into thinking that it has twice as much boost as it has and resulting in the PCM giving my truck more fuel. I'm sorry i don't know more about the sensor there is no technical information that tells how it turns the reference with no frequency into a signal with frequency. i do know that the reference voltage is 5 volts DC. i have access to the reference and signal wires if the need to be tapped into or rerouted for the circuit.
     
  10. Nov 25, 2009 #9
    i did find one web site that showed a schematic but was not very in depth i will try and locate the website and paste it in a reply.
     
  11. Nov 25, 2009 #10
    You could use a count-of-two digital counter preset another counter which is a count of three count down to zero at say 10 kHz. This would convert 120 Hz to 180 Hz.
    Bob S
     
  12. Nov 25, 2009 #11

    berkeman

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    It would be better to look at those signals with an oscilloscope, if possible. In case the shape of the AC signal makes a difference.
     
  13. Nov 25, 2009 #12
    if you could make up a schematic of the XOR circuit that is a frequency double that would be helpful. i'm not really electrically inclined. i know ohms law and watts law and resistance, voltage and amps but that's my extent of electrical knowledge.
     
  14. Nov 26, 2009 #13
    Hi-
    I don't have software to draw circuit for you, so I will try to describe it. First, you need to square up the rise and fall times of the input pulse. Use an LM324 as an input comparator. put about 1.2 volts on the neg input using a voltage divider (use an 10 k and a 1k resistor in series.. Use 100 ohms series input resistor to the positive input. Use a 10K ohm positive hysteresis feedback from LM324 output the the positive input.
    The LM324 output goes to two inputs of an XOR. One goes directly, and the other through a 10 microsecond delay. This will be a series 1k ohm resistor and a 1 nF shunt capacitor to ground. This should give a ~10 us long pulse on the front and back end of the input pulse. If the input pulse is shorter than this, you will have to shorten the delay. The output should be buffered with a transistor that mimics the original output pulse source / sink characteristics. The output transistor is either an npn with an open (pull-down) collector, or a collector output with a pull-up resistor. It is not clear whether the circuits in your truck use only the pulse edges, or the pulse width. If it uses the pulse width, a one-shot will have to be put between the LM324 and the XOR, and at the output of the XOR. So we really need more information from you on the pulse characteristics, and the circuits that receive the pulses.

    Whatever circiut you decide to build, make sure it is non-inverting.
    Bob S
     
    Last edited: Nov 26, 2009
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