Help for a project : Sciences PI Plate

Discussion in 'The Projects Forum' started by wanoo, Oct 22, 2013.

  1. wanoo

    Thread Starter New Member

    Oct 22, 2013
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    [​IMG]

    Hi every ones,

    I'm a young engenner in plant biotechnology. On my free time i try to create an open source plate for the Raspberry pi which has lots of functionality very usefull for science project (Plant growing, Invitro cell, hydroponic control, compotemental study...)

    I'm really a beginer in electronics, buti read a lot electronic book, looking schematic and see video.

    This plate have :
    • 8x relay 220V 5A control by a Darlington Array
      8x Analog input
      4x BNC connector connect to 4 Atlas Scientific Stamp (Ph, EC, DO...)
      RTC clock (to be sure of time when data are store on database)
      LCD screen 16x2 to facilite the reading without computer

    Before i order all parts and PCB, i wondering if you be able to check my schematic to validate it and maybe improve it :p

    Schematic Image files (2Mo)
    Fritzing files

    I have few question too :rolleyes: :

    1/ Can i connect all my ICs and LCD to my external power supply, i read on internet this is better than connect on the 5V from the Raspberry PI?

    2/ If i connect all 5V on my external supply how many amps i have to provide (the sum of all amps require by parts)?

    3/ Do you know an I2C IC can replace the 74HC4052 to make all the plate in I2C and made it usable by more than a Raspberry PI ? (if it interesting)

    4/ Which width is recommand for the wire on my pcb 24 mil (or smaller), and for the 220V Relay the biggest ??

    Thanks you for your help, and your website !
    Regards Erwan
     
    Last edited: Oct 22, 2013
  2. wanoo

    Thread Starter New Member

    Oct 22, 2013
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    no one can help me ?

    thanks
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,154
    3,061
    The Pi has some specification for the maximum power draw you can place on it. I don't know what that is, nor do I know how much power your arrangement needs, but my hunch is that you need far more power than you can ask from the Pi. Don't put it at risk - use an external supply.

    Yes, current sums. You have to plan for worst case (all relays active at once, for instance) since Murphy's law ensures that worst cases will happen.

    Out of my area.

    You mean the "traces" on the circuit board? This of course depends on the current in the trace, and again the currents sum for traces supplying more than one load. In addition to width, you can choose PCBs with thicker (deeper?) traces.
     
  4. #12

    Expert

    Nov 30, 2010
    16,345
    6,831
    Each question requires someone with expertise in that area. Every question you add reduces the number of people that know all the answers to all the questions.
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,154
    3,061
    That didn't stop me. :p
     
  6. #12

    Expert

    Nov 30, 2010
    16,345
    6,831
    At least you're not a know-it-all.:D
     
  7. wanoo

    Thread Starter New Member

    Oct 22, 2013
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    0
    Thank you for your help

    Ok good to know


    So if i use an external supply, which delivere the good current for all my compounds it's ok, but the IC chips have a maximun limit for current ? i don't want to burn it :D but i dont found clue on datasheet for the max current.

    oki

    Yeah trace on the circuit board, sorry for my english it's not my first language.

    Fritzing only proposing a pcb with 35 µm copper layer thicknes, on the soft i only can choose the width of the trace from 8mil to 128 mil

    other question ^^ :

    Can i use some capacitor for improving my circuit or this is useless ?

    Thanks
     
  8. wayneh

    Expert

    Sep 9, 2010
    12,154
    3,061
    Most ICs are designed to be powered directly from an "infinite" capacity power supply and do not rely on a limited capacity of supply. That is, they self-regulate the amount of power they use for their internal functions - like a light bulb you plug in the wall. Many ICs, however, can be damaged by placing too great a load on their output. In that case the power passing through the IC from the power supply into the load will cause too much heat generation and, poof.
    Most ICs benefit from a small bypass capacitor across the power pins, placed as closely to the IC as possible. For instance a 0.1µF ceramic.

    Capacitors can also be useful to act as low pass filters on analog inputs to remove noise, if the inputs are not expected to pass high frequencies.
     
    wanoo likes this.
  9. wanoo

    Thread Starter New Member

    Oct 22, 2013
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    Ok, so i have to be carefull for the need of compounds after the IC, normally it's ok, Only the darlington array have to deal with relay, which is the bigger comsummer of current, especially if all relays are switch "on".

    The analog sensor i plan to buy are more like "resistor" sensor (the resistence change in function of the parameter i will read (Temp, gaz....). So capacitor can increase the accurate of the mesure?

    For the IC by-pass i have to do something like that :

    [​IMG]

    Thanks for your precious help
     
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