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Thread: 5V vs 3.3V

  1. #1
    Constant Bitrate ACCLR8N's Avatar
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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. #2
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    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.

  3. #3
    Raw Wave
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    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).)

  4. #4
    Fusion Brain Creator 2k1Toaster's Avatar
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    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!
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  5. #5
    Fusion Brain Creator 2k1Toaster's Avatar
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    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

  6. #6
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    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)

  7. #7
    Fusion Brain Creator 2k1Toaster's Avatar
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    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

  8. #8
    Raw Wave
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    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).

  9. #9
    Fusion Brain Creator 2k1Toaster's Avatar
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    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

  10. #10
    Constant Bitrate ACCLR8N's Avatar
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    entropy...

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

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