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Posted 04-18-2010 at 06:33 PM by Reaper
I've debated on doing this for awhile. I know that I can buy these chips premade, smaller, probably better quality, but I wouldn't learn anything. That's why I decided to build my own MOSFET. In parts, it is cheaper than buying one, assuming you already have the required tools.

So basically, I am creating this for my own use, maybe if I can build it more efficiently, I would sell these things for $10 or $15.

The goals of each prototype are simple:

  1. To function
  2. Act as drop-in wiring harness with deans plugs
  3. CHEAP!!!
First Prototype
Homemade PCB
Basic Through-hole components
Second Prototype
Refine PCB
Shrink Size of chip (via Surface Mount Devices vs. through-hole devices)

Final Product
Refined PCB with silkscreen layer
Smallest Possible
efficient fabrication process
Potentiometer for ROF control?
3-rnd burst control?
I will be posting updates with my project as well as images\videos.
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  1. Old
    Person7's Avatar
    Really sounds great, best of luck with it.
    If you have not checked it out before you may want to take a look at the site at bottom, the guy who makes extreme-fire MOSFETs is a mod on the site and has posted some free diagrams and programming and such. Learning from other's mistakes can often reduce costs.,1/
    Posted 04-18-2010 at 09:55 PM by Person7 Person7 is offline
  2. Old
    dforces's Avatar
    i would love a 3 round burst control!
    Posted 04-19-2010 at 07:29 AM by dforces dforces is offline
  3. Old
    Torque's Avatar
    Good luck with your project. Most important thing in life is to learn something new.
    Posted 04-19-2010 at 10:18 AM by Torque Torque is offline
  4. Old
    anyone can put parts together following a schematic they found on the internet.

    The way you learn is understanding the electrical properties of the components and why the circuit does what it does. Being able to record what a circuit does is really how circuits are refined. Starting with a basic circuit you get a map of characteristics. From there you define what you'd like those characteristics to be. Then its just adding/replacing components until you find the results you are looking for.

    If i were to give you a suggestion, it would be to focus on features(once you get to the "later" point). There are lots of guys out there (arniesairsoft) that have already prototyped a simple 2 fet system that provide the means to make it for free (or pre assembled for very cheap). However, there are only a couple chip manufacturers out there that have brains to their systems. So far, this is where the market is lacking. We're stuck with person a or person b. It would be nice to see a chip which focuses on reliability and "true" features.

    Also, there isnt any reason why you cant just skip some of those steps above.
    Design it using an electronics workbench(or preferred program) use a breadboard to test it and just skip through hole design and go straight to surface mounting. But i will say you're not going to be able to save much space when it comes to using mosfets. They're sized based on the source/gain requirements you're needing. They also require heatsinking in our application or they'll just burn up.
    Posted 04-19-2010 at 12:20 PM by Mavrick Mavrick is offline
    Updated 04-19-2010 at 12:32 PM by Mavrick
  5. Old
    Reaper's Avatar
    i would like to implement much of the 'later' features without a microcontroller, but i don't know how possible that would be.
    Posted 04-19-2010 at 12:31 PM by Reaper Reaper is offline
  6. Old
    microcontroller is the recommended method IMO.
    Posted 04-19-2010 at 02:04 PM by Mavrick Mavrick is offline
  7. Old
    Can't wait to see the results. I agree with Mavrick about using a breadboard. It would save you some time and you won't waste your materials.
    Posted 04-19-2010 at 04:29 PM by Behindyou Behindyou is offline
  8. Old
    Loose's Avatar
    I make my own at home. It's fairly easy to do, well worth the investment. I don't know if you already have a MOSFET picked but I use the one listed below, as well as many other people.

    I've also used this one to save space, though it's power dissipation is not as good.
    Posted 04-20-2010 at 08:50 PM by Loose Loose is offline
  9. Old
    Reaper's Avatar
    I use irf3707. But I had a fail once I got my parts. I ordered 300k instead of 30k, they were the wrong kind too, like 1/8 watt. I would be better of using something bigger. And, my homemade pcb was a massive fail too. I ended up choosing mirror in the print options of my cad program when I didn't need to. So therefore, my pcb came out backwards. So now I'm in the process of etching a new board and ordering more parts from digikey.
    Posted 04-21-2010 at 09:35 AM by Reaper Reaper is offline
  10. Old
    you really ought to breadboard it out first so you dont waste materials on goof ups.

    Theres no point in soldiering components only to have to unsolder once you find you have the wrong component or find you need to modify the design.

    The benefit of breadboarding is that your circuit has the room to evolve beyond your basic design without the need to create new pcbs. Once you're satisfied you prototype to a pin hole grid type board and field test.

    Then when everything is working great you move to compacting it all into surface mounted printed pcbs.
    Posted 04-23-2010 at 10:00 AM by Mavrick Mavrick is offline
  11. Old
    Reaper's Avatar
    i did breadboard the original circuit. i went to radioshack and paid outrageous $.99 for some resistors. the pcb, i thought, needed to be mirrored, when it actually didn't.
    Posted 04-23-2010 at 11:42 AM by Reaper Reaper is offline
  12. Old
    Reaper's Avatar
    well, the MOSFET design is going to be redone. My schematic works, but requires four total wires to the gearbox, doesn't fit.
    Posted 04-25-2010 at 11:13 PM by Reaper Reaper is offline
  13. Old
    MechEng's Avatar

    I don't think you can get away with a direct dropin (without soldering and unsoldering at the trigger). Think about your design. There is a common positive side. Therefore you can use only three wires to the trigger/motor at the trigger. This can be a smaller diameter wire. Three wires in and two to the battery. Two of the three are the existing. Need to have user unsolder one side of the trigger and resolder it to the other side (should have two red wires here). Then your trigger wire to the 100ohm resistor goes to the side you unsoldered.
    Posted 04-26-2010 at 07:02 PM by MechEng MechEng is offline
  14. Old
    Reaper's Avatar
    Yeah, I learned that after I tried to do it. However, the good news is, that everything seems to be working well with the actual circuit. I'm going to work on my own wiring harness the next couple days, that way I can get a better feel for the revised design and how it will fit into the gun
    Posted 04-27-2010 at 09:55 AM by Reaper Reaper is offline

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