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  • Analogue inputs acting funny..

    Hey guys,

    I was just about to put my CarPC in my car but I thought I'd test my FB with my simulated steering wheel control circuit and I hooked everything up and noticed that my other ports were measuring a voltage but nothing was there. I took it out and setup a test config file that showed all the ports and their voltages. This is what I got:


    In this pic, I have 5v connected to port 1 (Port 1 on FB, Port 0 in configurator) and the other ports are reading these voltages. You will notice that the voltages decrease as the port increases, kinda interesting.

    Anyone know why this is? Do I have a fried board? I don't remember doing anything to fry it but who knows. In an attempt to get it to work, I pressed the reset button and switched off power and turned it back on and it said that it was version 3 not 4 when I reinstalled the drivers (I was desperate ).

    Any help would be greatly appreciated!
    Love

  • #2
    http://www.mp3car.com/vbulletin/fusi...ing-grazy.html
    Old Systems retired due to new car
    New system at design/prototype stage on BeagleBoard.

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    • #3
      Thanks, wasn't sure what to search for!
      Love

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      • #4
        Yup, it is normal. Just left over charge on the sampling capactior. Once you hookup another sensor, it will read correctly since it wont float anymore.
        Fusion Brain Version 6 Released!
        1.9in x 2.9in -- 47mm x 73mm
        30 Digital Outputs -- Directly drive a relay
        15 Analogue Inputs -- Read sensors like temperature, light, distance, acceleration, and more
        Buy now in the MP3Car.com Store

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        • #5
          Originally posted by 2k1Toaster View Post
          Yup, it is normal. Just left over charge on the sampling capactior. Once you hookup another sensor, it will read correctly since it wont float anymore.
          im not sure i ever saw an answer to this question, but is adding a jumper to blank inputs a safe way to zero them out? Will it do damage to the FB?
          mp3Car.com Senior Tech Blogger (Want a product reviewed? Contact me.)
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          • #6
            Originally posted by Sonicxtacy02 View Post
            im not sure i ever saw an answer to this question, but is adding a jumper to blank inputs a safe way to zero them out? Will it do damage to the FB?
            Why zero them out? If they aren't in use, then you aren't doing anything with them and they have the parasitics. As soon as you attach something to prevent them from floating such as a sensor or aything where you will use the input it will measure accurately. It is only apparent when measuring nothing.

            If you really want to make it go away, then (assuming you are using consecutive analogue inputs for your array of sensors) jumper between the AIN pin and GND. Be careful not to short power and ground as this will signal destruction of your Fusion Brain.
            Fusion Brain Version 6 Released!
            1.9in x 2.9in -- 47mm x 73mm
            30 Digital Outputs -- Directly drive a relay
            15 Analogue Inputs -- Read sensors like temperature, light, distance, acceleration, and more
            Buy now in the MP3Car.com Store

            Comment


            • #7
              Yea it was just a little weird, that's all. Just making sure my FB wasn't damaged.

              One quick question. When I hook up ~12V to the FB (and change the jumpers previous to the powerup), nothing really works. No AN inputs work and my MDX program errors out with .Net. When I hookup 12v while it is USB powered, everything works fine, AN inputs and digital outputs. Is this bad? I couldn't find anything written against this in the manual.
              Love

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              • #8
                Originally posted by rEegLer View Post
                Yea it was just a little weird, that's all. Just making sure my FB wasn't damaged.

                One quick question. When I hook up ~12V to the FB (and change the jumpers previous to the powerup), nothing really works. No AN inputs work and my MDX program errors out with .Net. When I hookup 12v while it is USB powered, everything works fine, AN inputs and digital outputs. Is this bad? I couldn't find anything written against this in the manual.
                It shouldn't happen. It isnt bad to use both power sources, but it's not really good practice and can induce ground loops, among other things. Can you take a picture of the jumpers in each config?

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                • #9
                  Originally posted by Sonicxtacy02 View Post
                  im not sure i ever saw an answer to this question, but is adding a jumper to blank inputs a safe way to zero them out? Will it do damage to the FB?
                  I'm running a jumper in front of each of my sensor inputs (every other port). The residual charge was throwing off all my sensors to some degree Tach, Speedo, oil pressure, fuel level. Even my digital signals such as check engine and alternator I have on on SPDT relays shunted to ground when off. http://www.mp3car.com/vbulletin/fusi...capacitor.html

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                  • #10
                    How accurately can the fb measure voltage? I have my steering wheel controls hooked up hookep up through a voltage divider and when I push one button, I'll get a voltage of 2.49577 for example but it flickers between that and 2.49166 somewhat randomly. I haven't tried the every-other port idea but I'm also not sure if it's the quality of my components or electrical noise.
                    Love

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                    • #11
                      I have several voltage dividers in my car as well. In theory FB is accurate to 0.005V. My experience in my car with all the noise and hoopla 0.015V, maybe 0.01V. Things like my speedometer I try to get close to 0.02V per unit of interest (i.e. 1 MPH= 0.0186V). Not the FB at issue, but everything else going on inside the car.

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                      • #12
                        Here is a pic of my FB config when 12V regulated is powering the FB:


                        You can see in this pic that the FAN is enabled and the there is no LED showing the dig output is enabled. That port is always outputting ~11.2V when a regulated 12V is supplied to the FB.


                        Here is my config when USB is powering the pics and 12V for DO's:


                        The DO led is lighting up, and is outputting ~11.37V


                        You said it wouldn't be a good practice to power the FB with 12v and USB but don't they share the same ground (in my CarPC they do but not my test setup)?
                        Love

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                        • #13
                          Originally posted by rEegLer View Post
                          Here is a pic of my FB config when 12V regulated is powering the FB:


                          You can see in this pic that the FAN is enabled and the there is no LED showing the dig output is enabled. That port is always outputting ~11.2V when a regulated 12V is supplied to the FB.


                          Here is my config when USB is powering the pics and 12V for DO's:


                          The DO led is lighting up, and is outputting ~11.37V


                          You said it wouldn't be a good practice to power the FB with 12v and USB but don't they share the same ground (in my CarPC they do but not my test setup)?
                          The output ports are switched ground. This means there is always +12v (or whatever else you power it with) on the output pins, but the related pin will only become a ground (completing the circuit) when turned on. So showing the input voltage all the time is normal.

                          As for not sharing the same ground, that is a valid point. Generally you should power it from a single source to prevent any problems. In most installations the grounds are shared (as with your CarPC). For testing, powering via USB but having the +12v connected to switch relays is the best method. It also prevents the FB from having to regulate the input voltage.
                          Fusion Brain Version 6 Released!
                          1.9in x 2.9in -- 47mm x 73mm
                          30 Digital Outputs -- Directly drive a relay
                          15 Analogue Inputs -- Read sensors like temperature, light, distance, acceleration, and more
                          Buy now in the MP3Car.com Store

                          Comment


                          • #14
                            Originally posted by ACCLR8N View Post
                            I have several voltage dividers in my car as well. In theory FB is accurate to 0.005V. My experience in my car with all the noise and hoopla 0.015V, maybe 0.01V. Things like my speedometer I try to get close to 0.02V per unit of interest (i.e. 1 MPH= 0.0186V). Not the FB at issue, but everything else going on inside the car.
                            This is exactly correct. Getting past 10bit DAC resolution costs money, and isnt needed at the hobbyist level.

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