First PCB Build / Photon Shield / MOSFET switch

Discussion in 'The Projects Forum' started by james211, Jun 20, 2016.

  1. james211

    Thread Starter Member

    May 29, 2012
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    I have a need for a shield for my DIY aquarium doser project. The unit runs on the particle photon, and they do not offer a MOSFET shield, only a mechanical relay shield, so I thought I'd try to build one. The hard part for me is that the shield needs to supply power for the photon (5v) and for the pumps (12v) with a maximum of 1.2amps. I have the schematic for the voltage regulator Particle uses on their mechanical relay shield, but what I'm unsure of is if it will be cost efficient for me to order a very small number of boards with pre-soldered SMD components or if it would be better to go with a dual output Mean Well switching power supply.

    I've attached the schematic of the power supply, as well the schematic (forgive me if its not good, its my first schematic) I created for the 4-switch N-Channel Mosfet board.

    As always, I appreciate everyones help.

    relay-shield-schematic-2.png

    photon_MOSFET_schem.jpg

    Thanks!
    Dustin
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    On your mosfet board, what connects to J1...J4? As shown and without considering what might be plugged into J1...J5, the mosfets will act as switches for the LEDs. Can't tell what is off to the left (J5):

    upload_2016-6-21_2-11-9.png

    How much current can the Photon sink?

    John
     
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    If you are making your own shield why not just include a 5V regulator circuit on your board too?
     
  4. james211

    Thread Starter Member

    May 29, 2012
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    J1-J4 are screw terminals for connecting 12v peristaltic pumps. J5 is the power input for motors. As for the Photon, it needs a minimum of 80mA with regulated voltage between 3.6-5.5v. The max output through VIN is 4.8v at 1amp.
     
  5. james211

    Thread Starter Member

    May 29, 2012
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    @mcgyvr , that's one of my questions here....with the first being I'm not sure I know how to incorporate the voltage regulator into my shield design, and second, if it will be cost effective given that the shield order might be a quantity of 5 or less.

    Also, the switch mode voltage regulator chip in the schematic is only available in a minimum of quantity 3000.

    Any suggestions on places to get quotes?
     
    Last edited: Jun 21, 2016
  6. Techno Tronix

    Member

    Jan 10, 2015
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    I think each photon can sink 25ma of current.
     
  7. james211

    Thread Starter Member

    May 29, 2012
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    Yes, thats correct....sorry I misread the questions.
    Input/Output current max ±25 mA
     
  8. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    That regulator is available on digikey with a min qty of 1 pc..
    Or pick another regulator... There are TONS out there..
    There are thousands to choose from.. Even a simple linear LM7805 (w/heatsink)

    Are you not going to be soldering the components either? boo :)

    If not why make your own and spend all that money when you can find simple mosfet boards already done..
    https://www.sparkfun.com/products/12959
    https://www.sparkfun.com/products/10618
    and many more..

    FWIW.. I buy all my PCB's from itead but I also solder my own components.. I believe itead has an assembly service too..
     
  9. james211

    Thread Starter Member

    May 29, 2012
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    I'm fine at soldering through hole, but I've failed miserably many times when soldering surface mount components. I have a nice Hakko soldering station.

    The primary reason I wanted to build my own PCB was to minimize the footprint and extra components.

    This whole purpose of my project is to offer a solution to people in my coral reef community a DIY option for a peristaltic doser. I'm not doing this for profit, its simply a shield they can purchase from me (will be priced to cover costs). So essentially I'm doing the leg work to help others out. The firmware and webpage programming are done, its just a matter of figuring out the hardware components now.
     
  10. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    This implies that the motor-supply ground will be through the Photon to its ground.
    upload_2016-6-21_10-12-29.png

    I suspect that is not what you meant. For devices with separate ground pins (e.g., many PIC MCU's), each needs to be grounded. There is not a robust internal connection between them. Thus, I would show both to ground (you probably mean common, not Earth ground, but that is not my point) and then show the power going to ground separately.

    If you use Eagle and not knowing how the Photon "device" is made (I quickly checked SF and didn't see it), it is possible that your board may not have those two grounds connected. Check the net name for both and be sure all of your grounds have the same name, if that is what you want. If you do a copper pour for ground, that type of error will be very obvious.

    John
     
  11. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Good luck with those "cheap" dosing heads.. They are garbage/don't last long.. (but are "low cost" for sure)
    Are you on reefcentral?

    And whats wrong with doing something for "profit" anymore.?
    All these "open source" kiddies are just spending their time/money and then just offering up everything for free/at cost..
    Make some damn money off it man.. Go for it.. Your only competition is Jebao at this time..

    Try itead assembly service though.. Their PCB's are great.. (best pricing hands down anywhere that I've seen and quality is excellent)

    But yeah.. Throw a regulator on it, make it so the photon plugs right into the shield and have an all in one solution.. Just need to hook up a 12V wallwart and be off and running..
    make sure to add protection (diodes,etc..) for when someone plugs in the USB to program it..
     
  12. james211

    Thread Starter Member

    May 29, 2012
    210
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    I'm on reef2reef, its the best forum I've been on hands down. I personally don't use the cheap friction heads, I use two different pumps brands. I took my jebao doser and replaced the pumps with Welco pumps. As for my other doser (which is running on the new firmware with Photon) I use APT instruments AC, 1.1mL/min pumps. They are incredible for the money.

    I've started building the schematic I downloaded, in eagle, but I'll probably need some help with choosing the components in the end, hopefully someone here can help me out. The circuit has protection built into it so its a good solution. I've never done this before, but since its all laid out in front of me I feel like this is a good way to start.

    I'll check out itead for PCB.

    Do you have a tank yourself @mcgyvr ?
     
  13. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Sure do.. Just downgraded though..
    Used to have a 120G 72" long w/bean animal overflow into a 40b sump and 20G fuge/algae scrubber waterfall from the 20G into sump.. nitrate/GFO reactors,etc... had ALL the bells and whistles

    Now I just downgraded a few weeks ago to only a 40B (no sump at all)..

    I just don't have the time anymore to maintain the larger tank.. (Got a new Jeep JKU and all my time/money goes into it)
     
  14. james211

    Thread Starter Member

    May 29, 2012
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    Nice..I have a 50g with 20g sump, its perfect for me and I want nothing more.

    Do you have enough expertise that once I get this thing laid out you'd be able to help me with the components? And how does it work with the components and the a factory doing the assembly? Do they have access to everything I'll need?

    I appreciate your help by the way!
     
  15. mcgyvr

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    Oct 15, 2009
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  16. george4657

    New Member

    Apr 12, 2016
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    The IRF540 requires 10 volts to turn on and I doubt the photon puts out that level. Look for a logic level FET like the IRL44 to get full turn on at 3.3 to 5 volts.
     
  17. james211

    Thread Starter Member

    May 29, 2012
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    @george4657 I have tested with the photon and it does work....not sure what to say other than it works. I'll check out the IRL44 as well though.

    Thank you!
     
  18. jpanhalt

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    Jan 18, 2008
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    The Vth (threshold voltage) is specified as being between 2 V and 4 V. That is the voltage at which the mosfet begins to turn on, which explains it working in your situation. However Rds (resistance between drain and source) at Vth is fairly high compared to when it it fully on. Thus, low currents will be no problem, but an amp or so with an RDS of 1 Ω will cause heating. The curves are in the datasheet.

    John
     
  19. james211

    Thread Starter Member

    May 29, 2012
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    Good to know, this is all a bit new to me. Been doing a lot of reading. So @george4657 recommended an IRL44, but a quick Google search resulted in nothing for that specific part. Am I missing something?

    The load current of the 12v pumps is no more than 400mA and at no time will no more than one pump being running at a time.
     
  20. jpanhalt

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    Jan 18, 2008
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    I think george meant the IRLZ44 (http://www.vishay.com/docs/91328/91328.pdf ). That is an older, logic level mosfet.

    There are ones today with even lover Vgs(on) or Rds(on) at 3.3V. Many (most) of the newer ones will be surface mount. I suggest going to DigiKey and using its parametric search to find an alternative. Mouser is another choice, but I prefer DigiKey's, even if I buy from Mouser.

    John
     
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