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Difficulty to find components

Discussion in 'General Electronics Discussion' started by Shirin, Aug 13, 2017.

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  1. Shirin

    Shirin

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    Aug 13, 2017
    Hello Guys,
    Im a master student in Design and Engineering and I'm designing a product but unfortunately I dont have enough information about electronic components and I want you to confirm the possibility of this idea or give me better solution.
    I tried to make a diagram block that I want you to check it if it needs to change sth.
    [​IMG]
    I explain about my idea:
    it should work with ibeacons and application ( through the cloud).
    so in the main device, i need the main board which can be programmable with android and bluetooth and wireless is integrated to the board.
    I chose raspberry pi module 3
    [​IMG]
    I need to find the right power supply. can you please help me even in this case?
    is 2.5 Amp battery enough for the whole system and how can I calclulate the battery charge?

    If you need more information, pleas let me know

    Thanks
    Shirin
     

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    Last edited: Aug 13, 2017
  2. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Your power pack needs to have at least the total current capability of ALL the systems connected to it - in this case, and according to your block diagram, this comprises the Raspi, the RTC and the Display. The 2.5A power pack will easily power the Raspi (400mA) and RTC (10mA) but you have to decide what device you want to use for the display.

    The recommended power pack (2.5A) only leaves you 900mA leeway for a display if the USB ports are fully loaded. If your display draws 500mA or less then that power pack will suffice.

    Whatever power pack you get ensure it has 'headroom' in supply current of at least 25%, preferably 50%.
     
  3. Shirin

    Shirin

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    Aug 13, 2017
    Thank you for your answer.
    I want to use chargeable Li-on battery, Is it possibile to charge it through wireless inductive charging system? if so, how whould be the diagram?
    another question is how can I calculate the battery consumption?
     
  4. kellys_eye

    kellys_eye

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    Jun 25, 2010
    The battery consumption is calculated in the same way as totalling the currents required for the Raspi and its peripheral devices. Make allowance for the length of time you want the portable unit to work for i.e. total current = 600mA, working time = 10 hours so battery capacity would be 0.6 x 10 = 6Ahr minimum.

    Wireless recharging is perfectly possible - use a datasheet search engine for details on current wireless charging control IC's and/or search for a ready-made module.
     
  5. Shirin

    Shirin

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    Aug 13, 2017

    What about the voltage? how can i calculate it?
    and how Can I understand how much power the whole system consumes in an hour?
     
  6. kellys_eye

    kellys_eye

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    Jun 25, 2010
    The voltage can be anything really - regulators can be used to drop or boost the voltage to what you need. If everything (or the majority of things) works at 12V then it's just common sense to use a 12V battery......

    Each part of the system will consume current - the Raspi is stated to consume 400mA (0.4A) and does so 'continuously' so consumes 0.4A per hour which is quoted as 0.4 Ampere-hour (Ahr) as far as battery capacity is concerned. This is how batteries are 'rated'.

    Total your current consumption and multiply by the number of hours you want it to work for before recharging - add some additional capacity to account for 'differences' in real world values.
     
  7. Shirin

    Shirin

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    Aug 13, 2017
    In this case, If the total device consume 750mA (the Raspi (400mA) and RTC (10mA) and display (260mA)), and I want to work for 24 hours, it should be a battey wirh 18A o_O? as I checked the battery become too large and heavy while mobile phones with small can be charged more than a day. Can you help me in this case?
    Thank you
     
  8. kellys_eye

    kellys_eye

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    Jun 25, 2010
    18 ampere-hours (18Ahr) is the correct way to state it.

    There are a number of different battery technologies, from disposable batteries to lead-acid, nickel cadmium, lithium, etc etc and your choice is determined by a number of factors not least of which are size, weight, recharge time etc.

    18 amp-hours at 12V is the same as 216 watt-hours (volts x amps) and may assist in making comparisons with batteries that are commonly used in laptops. A typical 17-inch display laptop may utilise a battery of 66 watt-hours so you're looking at a battery arrangement that comprises around FOUR TIMES the size (capacity) of a typical laptop.......

    This is why, when portable equipment is being designed, that energy-saving is very important. Careful choice of display type, using standby power when the equipment isn't being operated, opting for lower consumption modules with etc all chosen to minimise the strain on the batteries.

    Can you find a smaller/lower power display? Does it have to be colour LCD (consider mono displays or even e-ink), does the device require constant operation i.e. can you set it to power-saving mode when not making active processing etc etc.

    I can't make the choices for you.
     
  9. Shirin

    Shirin

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    Aug 13, 2017
    considering what you explained to me up to now,
    total device consumption is 2000mA if the USB ports are fully loaded.(the Raspi (400mA) and RTC (10mA) and display (260mA)), and I want to work for 24 hours,
    my display is 7 inch display. and the voltage needed as i checked in components technical description is around 3.7 V.
    therefore, is it right to search a for a Li-on polymer battery with 2000mA and 3.7 volt that works for 24 hours?
    then, with these quantity of volt and capacity, watt-hours is equal to 7.4 , how can I reach to 24 hours?
    is it better to choose a battery with higher capacity or higher voltage?
     
  10. kellys_eye

    kellys_eye

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    Jun 25, 2010
    3.7V x 2A = 7.4 watt-hours....... some way short of your desired goal of 216 watt-hours!!!

    The 3.7V would mean using a boost regulator to get the 5V and/or 12V required elsewhere in your design and the natural inefficiencies of such boost circuitry (90% at best) means more power consumption. Start 'high' (i.e with the highest operating voltage device) and regulate 'down' - there's no real saving as the 'down' regulation (buck regulator) will also have inefficiencies but getting a higher watt-hour capacity battery is easier by increasing the voltage than increasing the current.

    Whilst you can increase the volts or the amps it's your choice, but I suggest you look at ways of reducing the power consumption first as any way you look at it, without doing so the battery will be quite large and require longer to charge.

    How 'portable' do you want this device to be anyway? Understand that there aren't very many portable (rechargeable) devices that will work for 24 hours non-stop. Even your mobile phone will only work (talk-time) for 8-10 hours - it spends most of its time doing 'nothing'..... the key to 'all' mobile devices - downtime.

    Look up 'sleep mode' for any of the devices you are using.
     
  11. Shirin

    Shirin

    7
    0
    Aug 13, 2017
    exactly, its the same as other portable devices, it's not on 24h , it works like alarm and indoor navigator in different times of the day,so I even need stand by .
     
  12. Irv

    Irv

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    Jun 7, 2017
    Your problem is the Raspberry PI. While it's a neat little computer, it has a terrific appetite.
    I believe that if you define your problem more "tightly", meaning specify exactly what it is expected to do, and then choose the proper hardware that can do that and nothing more, you'll have a viable product. That is what the cell phone makers have done, and as far as I know, none of them run on a RPi.
     
  13. kellys_eye

    kellys_eye

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    Jun 25, 2010
    In which case you need to adjust your power consumption assessments to reflect the actual usage and you'll find the demands on battery capacity come down considerably.

    Match that with any power-down/standby function you can implement in software (and hardware) and you'll eventually end up with a reasonable battery demand/requirement.
     
  14. Shirin

    Shirin

    7
    0
    Aug 13, 2017
    as you see in diagram.I expected my product to work as an alarm and indoor navigator based on ibeacons and cloud system. I chose RPi because of the cost and I tought it could be compatible with my requests, do you have any other suggestion?
     
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