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Thread: IQ3 display averaging for fuel level.

  1. #1

    Default IQ3 display averaging for fuel level.

    More of a feature request than a tech support question really.

    Would it be possible for a future IQ3 firmware release to include a much larger averaging filter for display of fuel level on the dash? The current maximum setting (15) still has the fuel level jumping around by some litres in response to bumps and G loading because of the float inside the fuel tank heaving around. If the filtering could be extended to effectively average the reading over a period of some seconds, it would provide a display that would be far easier to read at a glance.

    If that is not possible, would it be feasible for me to add a capacitor in between the sensor input and ground terminals (I am using an input on a USM for this) to effectivly extend the time constant of the circuit and smooth the input signal? My only concern there would be that I might need a fairly substantial capacitor to provide any significant smoothing and it adds another point of unreliability, just another component to fail.

    Edited to add some detail.

    I have been sitting and chewing it over with another ex techo mate, the circuit I am thinking of would be to use the +5V supply from the USM with a pull up resistor of approximately the same value as the variable resistor in the tank, effectively making a voltage divider circuit of it and goving me a voltage range of approx 0V to 2.5V to give good resolution (The resistor in the tank is approx 230 ohms to zero ohms, I still need to measure it properly) I was planning to use the chassis ground for this circuit rather than the ground in the USM as the level resistor in the tank is grounded to the chassis at one end and using the USM ground may lead to ground loop problems. I will draw a circuit diagram when I have the time and put it up here for people to have a look at.

    This voltage divider circuit between the pull up and tank sensor could then be input to an RC (resistive-capacitive) circuit that is between the output of the tank sensor/pull up combination and chassis ground. The junction between the resistor and capacitor is where the sensor input to the USM would be connected, using the time constant of the R-C circuit to average the fuel level over a longer period.

    I only have a couple of questions of Racepak before I have a crack at it.

    Is the input impedance of the USM known? I would assume it is high, in the order of meg-ohms. If it is low impedance I need to account for that in my workings.

    The only other question would be what is typically used for pull up resistors on fuel level inputs? I was planning to roughly equal the maximum resistance of the sensor in the tank to provide good resolution as the internal pull up leaves the full range of the tank sensor providing a very small voltage swing.

    A 230 ohm pull up would give approximately 22 milliamps through the tank sensor when it is at minimum resistance, I don't want to go burning out the variable resistor or getting it overly hot. It also allows for the pull up resistor to be a moderate poer rating as the max power dissipation would be about 0.1 watts. Is the USM capable of sourcing this sort of current for asingle sensor without any problems?



  2. #2

    Default Re: IQ3 display averaging for fuel level.

    Apologies for a very rough (Hand sketched) circuit but this is what I was invisaging if a firmware change to allow much longer averaging is either not possible or a long way from being done. The valuses of all resistors are approximate or yet to be determined, as would be the capacitor value. I would appreciate if any of the Racepak Tech people could comment if they see any issue with doing this. the pupose of this circuit would be to make use of the R-C charging time to smooth out voltage swings due to bumps and corners upsetting the float level in the fuel tank.

    As per my original post, I would look to use the chassis earth rather than the ground in the USM as the varistor in the tank is grounded to the chassis at one end and using the USM ground could result in earth loops and stray currents. I also wanted to keep the pullup resistor at approximately the maximum value of the in tank varistor to retain good resolution, or am I better to use the inbuilt pullup? What is the value of this internal pullup ressitor? It appears to be much higher given the calibration figures generated if I do use it so my preference would be an external pullup to the +5V in the USM so that I am not trying to fit full tank to empty tank into a 1V range from a 5V supply rail. At 230 ohms pullup there would be around 20 milliamps maximum flowing due to the 5V supply. a 230 ohm 1w ressitor would be fine.

  3. #3

    Default Re: IQ3 display averaging for fuel level.

    I am full of questions today!

    One event I run my car it is a regularity type event and I may be required to remove the GPS antenna from my IQ3 so they can be sure I am not displaying lap times in the car. I would like to arrange a second speed input as there is also a pit lane speed limit which is rigidly enforced with penalties that can put a team out of the running for a minor infringement.

    I have a wheel speed sensor on the car, would it be possible to input this to the USM (It is a hall effect device) and using the calibration data of 4 pulses per revolution this would equate 1 RPM at the wheels (Four pulses from the four wheel studs) as approximately .12kmh. Can I use four pulses per revolution so four pulses per second equals 1 rpm, and 0=0, 1 = 0.12 calibration figures to generate an output in KMH from this sensor using the USM?

  4. #4

    Default Re: IQ3 display averaging for fuel level.

    You might want to take a look at ... duct_id=52 as a solution

  5. #5

    Default Re: IQ3 display averaging for fuel level.

    I will have to contact them, it is very close to what I need and even after considering post to Australia probably cheap enough that it is not worth making something myself. After two hours work, if I was paying myself to do it, this device would be cheaper!

    The only issue I can see is that it is for 0 to 110 ohm sensors and mine runs to more like 230 ohms. If they do a higher ohm version it could be exactly what I need.

  6. #6

    Default Re: IQ3 display averaging for fuel level.

    Wow thanks for posting that up - I think I may get one too because my fuel reading is all over the place too and I've just been dealing with it.

    Blue they can do other resistance readings it seems. Look at this pdf here: ... A_rev-.pdf

  7. #7

    Default Re: IQ3 display averaging for fuel level.

    That is looking like exactly what I need. I can live with a jumpy reading for a little while as the fuel level will not be on my default displayed page in normal events (Mainly circuit sprint and open course hillclimbs) and it will just be checked on between runs to check on the level with the car stationary, but at one event we compete in the car is on track for a substantial period of time and can use up to half a tank of fuel for one stint so I will want to display it on the main screen for that event.

    I will email them and see what they have to say about specific sender resistances. Hopefully it ends up at a nice price landed in Australia as I really do prefer installing to prototyping!

  8. #8

    Default Re: IQ3 display averaging for fuel level.

    i can only use my fuel level when the car is stationary
    on the udx dash i used to have on the custom calibration it never reacted too quick

  9. #9

    Default Re: IQ3 display averaging for fuel level.

    I am still waiting for a reply with regard to the signal conditioner. I might try them again.

  10. #10

    Default Re: IQ3 display averaging for fuel level.

    Just thought I should post up here to keep the ball rolling.

    The IRQ signal conditioning unit is actually still a development item. They are sending me one as we speak, called to suit my fuel sender as measured by myself with an ohmmeter on the condition that I give them a detailed report on my experience with it, which is entirely fair. Ivan, who I have been dealing with at IRQ seems to be pretty switched on. The best way to test I think is that I am going to log the input with and without the signal conditioner on consecutive runs so that the fuel level in the tank is similar and send them the logs. The conditioner is more than just an LCR filter circuit, though I suspect that there is one of those in the input stage, there are also some statistical tricks played to ignore spurious readings for the likes of a scratchy variable resistor.

    I will report in here as to how it goes as this should be a really handy item for people with display of logging dashes (Or even straight data loggers) and the price looks very reasonable.

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