A Surprisingly Accurate Digital LC Meter?

Discussion in 'The Projects Forum' started by AchMED, Jul 3, 2009.

  1. AchMED

    Thread Starter Active Member

    Aug 5, 2008
    41
    0
    Has anyone built this LC meter? The meter uses the PIC16F628.


    http://ironbark.bendigo.latrobe.edu.au/~rice/lc/index2.html

    I want to change the relay out with a FET. I read through the code and to me it looks like an N-FET low side should do the trick. Here is a code snip that makes me think I could use an N-FET.

    Code ( (Unknown Language)):
    1.  
    2. #define relay   PORTB,7                    ; Switches Ccal
    3.    
    4.   bcf       relay                ; Remove Ccal
    5.    
    6.   and another putting Ccal in the circuit.
    7.    
    8.   bsf       relay                ; Add standard capacitor
    9.  
    10.  
    To me this looks like setting portb, 7 high turns the relay on, and clearing it turns it off.

    But when I read the FAQ there is this.

    http://ironbark.bendigo.latrobe.edu.au/~rice/lc/faq.html

    "Can I replace the relay with a 2N7000 FET?"

    "This should be possible (with a "slight" change to the program to invert the control signal and a "slight" loss of accuracy).

    I did try a NPN transistor in an early version of the prototype, but wasn't happy with the stability. This was probably due mainly to my "rat's nest" construction. My excuse for using a relay is pure laziness - having got it working, I wasn't going to mess with it."

    Hence my confusion.


    This may refer to older design where he uses a PNP to control the relay?
     
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