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  • 5V vs 3.3V

    Yeah, another thread from me. Didn't want to take the V6 board pre-order thread off on a tangent. Anybody else disappointed with the switch to 3.3V? I'm guessing it is too late to change if it was even possible with the new chips. Many automotive OEM and aftermarket sensors are 5V based that I want to get readings from. Now they will require dividers adding in some tolerance. Now I'll have 12v, 5v and 3.3v circuits to keep track of if I mix and match boards. 5V at 0.0049 gives me 1020 data points. 3.3V at 0.0032, 1030 measuring points. In my car I was happy to get 0.01V resolution with all the noise, that would only be 330 plot points. I'm not feeling the love for the new hotness.

    What is the advantage that I'm missing? Should I order up V4 boards before they are gone?

  • #2
    I was wondering the reasoning for the switch myself. I have 22 analogue inputs, over half are 5v sensors. I'm starting to think I may have to stick to the v4's as well. To bad, I was really looking to free up a USB port.

    Comment


    • #3
      It's only a 2:1 resistor divider.

      The number of data points does not change with the ADC's voltage. (It's the number of bits - ie, 1024 (for sensors with better than 0.1% accuracy, linearity etc).)

      Comment


      • #4
        The change is because it is needed. 5v is pretty much dead in the eyes of the industry. Any new chips with new feautres run off of 3.3v. The stuff I work with uses 1.2v and 1.8v signals for their "high power" runs.

        All sensors we sell excluding the current ultrasonic sensor all work with 3.3v. The resolution is the same in terms of it scaling over the supplied voltage.

        For instance, if you give the thermometer 5v, it scales a signal between 0v and 5v dependant on temperature. If you give it 3v, it scales a signal between 0v and 3v. Most of your automotive sensors are resistive based as well meaning you can generally supply them with 3.3 and they will be happy.

        In an ideal world, the accuracy would be identical over the scaling.

        The only downside is that the same amount of noise makes more of a problem. The compensation for this is that the current ADC is more sensitive and much more accurate over the sweep than the current version. So any error introduced in the V3/V4 because of a lesser converter will be similar to any error introduced in the V6 because of the smaller voltage. In noisy situations, it will be a wash. In good situations, it will be much much better.

        What sensors are you worried about not being able to use?
        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


        • #5
          Just be glad you arent having to deal with the USB amp I working on... 50v, 12v, 3.3v, and 1.8v rails all swinging around... PITA.
          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


          • #6
            I'm not so much worried about not being able to use them, but rather the effort it may or may not take to get them to work. If I have to start putting in voltage dividers on all my sensors than it becomes a PITA, I just spent 3 weeks switching 41 outputs and 22 inputs to solid state all with opto's to protect the brains rather than the relays I was using, but if your saying the automotive sensors work then I'll switch over to at least one v6

            Currently running;

            methanol psi
            Wideband o2 afr
            oil pressure
            oil temp
            fuel pressure
            coolant temp
            heat exchanger temp
            trans pressure
            trans temp
            air intake temp
            5 of your temp sensors (you say these shouldn't be a problem)
            7 inputs monitoring doors, hood, trunk, etc (these are no problem as they pull their voltage from the brains analogue + for each circuit)

            Comment


            • #7
              I should clarify that not all automotive sensors will work, just like alot of them wont work at 5v either. But it is a good probability that they will. And at worst case, then it is a simple resistive divider to scale it down with no isolation. I guess we can provide some simple boards to do just that if needed.
              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


              • #8
                And to think I get criticised for long answers
                Or are people powering all their 5V-15V sensors from the FB?

                The noise will NOT increase (assuming the scaling is done at the FB as it shoud be - ie, NOT at the sensor).

                Comment


                • #9
                  Well if being scaled at the FB, then no additional noise. However, if powering it off of the FB to begin with, then it is `prescaled` and noise could be an issue.

                  However the power supply is much more accurate as is the ADC, so in all I think even with extra noise it should be better than the current version.
                  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


                  • #10
                    entropy...

                    You will need a different function to return the correct Fahrenheit/Celsius values from one of your temp sensors correct?

                    Comment


                    • #11
                      Not in MDX. We report the digital value. Since the thermometer is linear at both 3.3v and 5v, if it says 4v with a 5v VCC, it is going to read in 4/5*1023 = 818 and report that to the software. If it has a 3.3v VCC, it will report around 2.64v which is 2.64v/3.3*1023 = 818.
                      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


                      • #12
                        Sooo.. I am only getting into this for a nice customizable LCD gauge in my track car. Given that every single thing on my car is 5v and things I will be adding (oil pressure, etc) will be 5v, should I just stick with finding a used v4?

                        Comment


                        • #13
                          Originally posted by night View Post
                          Sooo.. I am only getting into this for a nice customizable LCD gauge in my track car. Given that every single thing on my car is 5v and things I will be adding (oil pressure, etc) will be 5v, should I just stick with finding a used v4?
                          You sure about that? Most things in a car are 12v. Or they are resistive, and then will work on any supply 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
                            unless i am misunderstanding how this works with software.
                            My car is an OBD1 Honda with tuning software + data logging. That software has built in gauges but they are very basic. However, with that the idea was set to use a full time pc in the car for gauges (and multiple webcams later on for track lap recording). I happened on this and with the 5v fusion would be awesome.
                            "Every single thing in the car" was referring to engine controls. IAT, ECT, TPS, MAP, Wideband, etc. All ECU inputs are 5v reference. Then add a couple 5v pulse converters and I can pass everything through for a custom gauge.
                            Maybe even an accelerometer for some ghetto street tuning if I can figure out it's accuracy.

                            I am frankly wired the hell out atm. I just finally finished a complete custom harness for the engine/car. So any extra work makes me cringe.

                            Comment


                            • #15
                              5V interfaces are not the same as a 5V supply.

                              Most inputs can EASILY be scaled (down) to 5V, or 3.3V etc. (Resistive aka voltage divider - usually two 2c resistors.) That's for both digital and analog inputs.

                              And most digital outputs are ground (open collector) switching so the target's voltage does not matter.

                              Only output inversion and analog output upscaling requires more complexity (eg amaybe resistors AND a transistor).

                              Comment

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