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HELP! Building Keyless Access for Automobile

Discussion in 'Microcontrollers' started by thekyguy11, Jan 15, 2009.

  1. arhi

    arhi Member

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    those 50mA should be enough (unless you drive that 18f1320 at max speed .. miscalculate the be current for the transistors and ... and .. and .. ) ..

    on the other hand, I am known for over dimensioning everything :D so 500mA - 1A is something i'd go for .. you have to search the web / stores for some auotomotive ready voltage regulator with that ratings .. I'm sure you can find some...
     
  2. thekyguy11

    thekyguy11 New Member

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    Can I just use the RFID output and a transistor/relay to supply power to the regulator? I could use a 555 timer to delay shutdown if RFID is deactivated while the IGN/Engine is on? That would take care of battery draw when not in use.
     
    Last edited: Mar 9, 2009
  3. thekyguy11

    thekyguy11 New Member

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    I posted my full schematic here .I find that more people are exposed to my questions if I start a new thread for them.
     
    Last edited: Mar 11, 2009
  4. dave

    Dave New Member

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  5. thekyguy11

    thekyguy11 New Member

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    In another thread I started about the rpm switch, it was brought to my attention that I should just have the RPM input go right into the PIC and use the code to decide when a certain rpm has been reached. Can someone help me with that code? They mentioned a frequency counter???

    And here is my schematic...
     

    Attached Files:

    Last edited: Mar 14, 2009
    • Like Like x 1
  6. be80be

    be80be Well-Known Member

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    You can use the PWM Capture and Compare I haven't tried it.
     
  7. thekyguy11

    thekyguy11 New Member

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    OK, here is my updated schematic. I have changed it quite a bit. I tried to make the inputs and outputs follow the examples in Nigel's PIC tutorial. Let me know if you see any problems.

    Pommie, I would like to test the RPM code you wrote for me in that other thread and then I'll begin changing the main code to suit my project. Here is my list of changes that need to be made to the code, let me know if I am forgetting anything.

    1- Go back to all digital inputs
    2- Check/Change all I/O's to match pin locations shown in the schematic
    3- Eliminate the section of code that was written to multiplex the LED's
    4- Integrate the RPM input code

    Then I think I am ready to order parts and build a prototype on a bread board and test it out!!!
     

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  8. jimlovell777

    jimlovell777 New Member

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    Forgive my ignorance here but if I'm not mistaken the 7805 regulator is always powered regardless of the vehicles on or off status and the 50 OHM resistor will drain 100mA all by it's lonesome. Add the draw of the rest of the circuit and the draw of the RFID reader (25mA avg, I know because I own the same make and model) and you're over budget on standby current. Take a day off driving and you'll likely have a dead battery. I contended with the same issue for a similar project and current draw is paramount, it's needs to be kept in check for reliable use.
     
  9. 3v0

    3v0 Coop Build Coordinator Forum Supporter

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    It is much worse then that. As arhi said several posts ago a 7805 is a poor choice for use in a car. The chip makers have come up with a range of regulators designed for use in the harsh automotive electrical system.

    The regulator circuit provided by superbrew is 10 years old and may not do as good a job as a special built regulator.

    Regardless of where you live you can check Mouser, Newark, and Digikey to find the numbers more suitable parts.

    3v0

     
  10. thekyguy11

    thekyguy11 New Member

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    well, I'm all for using that specialty regulator listed before, I'm just not sure how I would connect it up. If someone could help me with that part, it would be great!!!
     

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