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Thread: Intelligent Fan Control

  1. #21
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    One question never answered was the load on the driver. Yes if you add 4 transistors you add 4x the load on the driver that is turning them on and off. You need to make sure it doesn't overload whatever microprocessor you use.

    The actual microprocessor you use really doesn't matter. The mentioned PIC chips have been around much longer than some of the newer stuff. Some of these newer chips are powerful but you have pluses and minuses with each one. You could add a Parallax Propeller that would be less than $10 to your circuit that supports 32 pins of IO that can be configured however you want. If you want them to be configured to do Serial/USB then you can do that or whatever. But then you need to learn its method of doing stuff. It uses basic and comes with 64k of ram of which 32k is used for the BASIC interpreter.

    But again, it doesn't really matter what you choose because they are all going to require other components and require some sort of custom circuit board to get it as cheap and reliable as possible. And I doubt if the cost difference is $15 instead of $30 it is going to be a big deal. If the difference was $15 or $150+ then I would be concerned.

    If the load of your MOSFET circuit is too much for your PIC driver then the easy solution is to put another Transistor prior to the MOSFETS. This one should be sized to meet the driver load.

  2. #22
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    Quote Originally Posted by redheadedrod View Post
    One question never answered was the load on the driver.
    .......
    If the load of your MOSFET circuit is too much for your PIC driver then the easy solution is to put another Transistor prior to the MOSFETS. This one should be sized to meet the driver load.
    In response to #1, PICs etc can provide at least mA. A MOSFET is nA; uA at the most. What load?

    In response to #1, transistors are mA. See In response to #1. Or try to understand the loading of a MOSFET on a circuit compared the the loading (and design) of a transistor.
    Last edited by OldSpark; 11-02-2013 at 10:11 AM.

  3. #23
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    Quote Originally Posted by OldSpark View Post
    In response to #1, PICs etc can provide at least mA. A MOSFET is nA; uA at the most. What load?

    In response to #1, transistors are mA. See In response to #1. Or try to understand the loading of a MOSFET on a circuit compared the the loading (and design) of a transistor.
    I really don't care OS, if you are going to respond in this manner you need a time out. No need to be arrogant. If you are going to suggest something then you need to explain this information up front. The OP asked a question about the load which you ignored so I answered in an accurate manner. The OP could look up the loads and find out for himself that the load is minimal. However with almost unlimited number of processors, transistors, MOSFETS and other components you can not make blank generic statements and expect it to be the case in all cases. Anyone building circuits needs to check all ratings and such and make sure the components they are using fit withing the desired parameters. Just because every MOSFET you ever used takes very small load to run it doesn't mean some cheap Chinese knockoff doesn't have a higher load requirement and there is no excuse for not at least checking the parameters of the devices being used against the design needs. When you assume such things you get burned eventually. And sometimes when you follow those assumptions without checking them out first then when you get burned you don't understand why until you look through everything and find out you missed it at step one of a 12 step program. But they do say the first step is denial...

    And yes I have been burned by making such assumptions in the past so I NEVER make assumptions and always check twice to make sure.
    Last edited by redheadedrod; 11-02-2013 at 08:25 PM.

  4. #24
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    LOL - time out! You've had yours have you?

    I thought the OP understood
    Quote Originally Posted by OldSpark View Post
    A 14uA 08M2 driving a 100A switching MOSFET? Simple!
    .
    Or that if still an issue, AutoWiz would ask.

    And not that I see this as a "design detail" thread yet, maybe YOU can provide an example of where a MOSFET's Gate current taxed a PIC or uPC etc output?


    Not that arrogance was intended, but to suggest "... put another Transistor prior to the MOSFETS...! Huh? Aside from assuming you mean Transistor as in a bce type (ie - not FETs etc), I think the practice of fan-out or using a main switcher to control others is well understood, else would be dealt with later. (EG - one MOSFET or relay to control many; one battery isolator "smarts" to drive several battery isolators, etc.)


    But let the OP ask.
    I essentially wanted to crush else qualify your "put another Transistor prior to the MOSFETS".

  5. #25
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    so I have rebuilt my autolamp module in the smallest fashion I could with this picaxe 08m2+. I hope this is small enough for your liking/acceptance OS. I still have to program it and add +5v, gnd, and marker lamp and headlight relay out wires. I used npn transistors. they say they can handle 500ma so we will see what we get.
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  6. #26
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    forgot to add the pull up resistor for the ldr. here's what it looks like now...
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  7. #27
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    It might be too small - it might not fit the program! (LOL)

    Good to see I'm not the only one with rat's (or Osprey?) nest wiring. Mind you, 1/8W resistors on a SMD 08M2 are smaller.
    That's the thing with "small" circuits - why bother with a PCB? I'd often rat's nest prototypes and they'd work. I learned "if it ain't broke, don't touch it" - so many times I'd transfer to vero or matrix board and I'd never get them working.


    But a big CONGRATS. Now you've broken the ice you might find so many things suited to a PICAXE. I know many circuit complex things that are just so easy on an 08M2 - eg, ramp-up and down LED dimming (puddle lights etc); alarms; timers; ....

  8. #28
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    rat's nest wiring? damn you OS, you are an impossible person to please. I conceded I was being arrogant and rejecting a new idea and I built what you suggested. why? why can't that be enough? why must you challenge me to build yet a third autolamp module?

  9. #29
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    Looks like you should have bought a few more chips, nice work in such a short period of time. Following to see what's next. SNO

  10. #30
    Maximum Bitrate rray's Avatar
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    Haha! I thought I was the only guy who builds device on device circuits to miniturize them!

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