Will this circuit work? (Please look before getting batch fabricated)

Discussion in 'The Projects Forum' started by Toebs, Oct 9, 2014.

  1. Toebs

    Thread Starter Member

    Oct 9, 2014
    52
    1
    Hello all

    As you can see this is my first post on this forum. I have been following the forum as a guest viewer only for a while, but now it's time for my first post :).

    I have made a schematic of a wifi sensor node with an internal temp/humidity sensor and inputs for 4 external analog moisture sensors.
    I am going to start by having a small batch of 10 units produced and assembled, but before i order it, I would really appreciate some secondary opinion of the design.
    I am mostly not sure about if i connected the USB plug and the 5V -> 3.3V v-reg (AP1117) and the Torex XC9128 3.3V boost supply from the batteries correctly to each other.

    Will I waste my money sending this to the PCB manufacturer?
    Please take a look at schematics and tell me what you think :)




    The moisture sensor is VH400 ( http://www.vegetronix.com/Products/VH400/ )
    The moisture sensors outputs 0-3.3V and runs of 3.3V-20V
     
  2. wayneh

    Expert

    Sep 9, 2010
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    You're going straight to PCB without making a breadboard prototype? Brave.
     
  3. JWHassler

    Member

    Sep 25, 2013
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    You would be better off posting your schematic for critique.. it's difficult to read a PCB layout.
    Once you're happy with the schematic, the layout is much easier to trust.

    The layout tool will often have a Design Rule Check, which you should also use. There are also on-line Gerber-file viewers
    Some PCB manufacturers will do rule-checks.

    OhhhhKay... you did post a schematic, and the only question that arises is the slightly different wiring on J30 vs that of J31,J32 and J33.
    Everything else looks OK (to someone who's not paying to get it fabbed.)

    I agree with wayneh that it's brave to build it without a breadboard prototype, but you could choose to regard the first PCB as your prototype. The schematic shows signs of careful design work: if the PCB layout was that careful, too, you should have a usable (if not 100% perfect) PCB.

    (Again: not paying, but good luck.)
     
    Last edited: Oct 9, 2014
  4. Toebs

    Thread Starter Member

    Oct 9, 2014
    52
    1
    First of all: Wow, fast and good feedback, amazing! :D

    Wayneh: Yeah i would prefer to try it out on a bread board first, and i do that with parts of the circuit, but I find that some of the components i use are not available in non-SMT format, and thus I dont know how to prototype easily. Any advice?

    JWHassler: Had not seen that screwup on J30, thank you!
     
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    I keep a smal supply of SMT's with soldered on leads for prototyping.
     
  6. wayneh

    Expert

    Sep 9, 2010
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    And I think there are jigs to accomplish that - a thing with legs that you solder a SMT component to.
     
  7. Sensacell

    Well-Known Member

    Jun 19, 2012
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    I usually cobble together a crude but working prototype using eval boards, DIP packages, SMD surfboards etc, on a big piece of perf board.
    The main advantage to this approach is time savings- you get the hardware working very quickly, this savings trickles down to firmware and software timelines too.
    It's almost impossible to get the schematic right the first go around, if you go to a SMD PCB straight off, roach wiring is very difficult, and sometimes impossible.

    You will probably need to re-spin the board 2-3 times before it's right.
     
  8. Toebs

    Thread Starter Member

    Oct 9, 2014
    52
    1
    Thanks guys! Sounds like I should get my self a nice collection of components for testing purposes, and try to make them fit for use with breadboard.
    Maybe you will also take a quick look at this next schematic, which I will also try to prototype.
    I have attached schematic of a relay board with a flow sensor input.
    I took a working design and added 5V psu and flow sensor input. I also changed the terminals to the relays so each has a GND and connects to 24Vac when relay is on (normal open).
    Lastly i added the SI7021 humidity and temperature i2c sensor
     
  9. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Prototyping with SMD parts is a breeze if you have adapters for the chips like so:

    [​IMG]

    Source: Ebay, search for "SOIC Adapters"

    I find it helpful to have a breadboard base made from a sea of plated thru holes like so:

    [​IMG]

    Again, climb onto EBay and search for "Double Side PCB Prototype Board."

    As the holes are 0.1" apart then play well with the above adapters. Also if you keep to 0805 SMD caps & resistors these fit very well between the thru hold donuts. SOT-23 transistors can also go down directly if you twist them 45 degrees.

    They come in many sizes from 2x8cm to 15x20cm.
     
  10. Toebs

    Thread Starter Member

    Oct 9, 2014
    52
    1
    Ordered the 55pcs kit shown above, and alot of components. Ready to prototype :)
     
  11. Lestraveled

    Well-Known Member

    May 19, 2014
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    I noticed that pin 2 and 3 of J30 is shorted together. This is not the same as your other inputs.
     
  12. Toebs

    Thread Starter Member

    Oct 9, 2014
    52
    1
    Just to follow up. I fixed what was pointed out in this thread (thanks to all of you :)), prottyped with some SMD components. Had 10pcs PCBA by ITEAD studio and it all works. However 1 thing I missed, I somehow swapped the I2C lines, SCL to SDA and SDA to SCL, maybe I was thinking UART duh.. :). Well nothing that couldnt be fixed by hand.
    Again thanks for the help!
     
    ErnieM likes this.
  13. wayneh

    Expert

    Sep 9, 2010
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    Congrats!
     
  14. JWHassler

    Member

    Sep 25, 2013
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    Ditto congrat.
     
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