THIS simple PIC-based unit was designed to measure and display the values of inductors and capacitors.As a by-product of the technique used.it can also display the frequency of an external 0V/ +5V signal source The ranges are approximately:
Capacitance : 1pF to 6500uF
Inductance : 1uH to 10H
Frequency : 0.05Hz to 5MHz
The design is based upon the concept that osillators can be constructed from CMOS NAND gates or inverters.and that their oscillation frequency depends on the valuesof inductance. capacitance and resistance in their feedback paths. Using a suitable microconteroller. Such as one from the PIC 16F62x or PIC 16F87x
families. software can read the frequency of an oscillator and calculate the value of the ot- her components are known.In this design. A PIC16F628 is used and the results are output to an alphanumeric liquid crystal display (I.c.d.). One technique for using an inductor in a CMOS oscillator circuit is that shown in Fig.1.Here the oscillation frequency is determined by the formula:
F = _______1_______
F = _______1_______
2 x 7 x / ( L x C )
where:
F = frequency
C = C1 x C2
C1 x C2
L = inductance
7 = 22/7
Using this formula. If any two values are known. The third can be readily calculated For instance . if C and F are known. Than I can be calculated using the formula:
( 1_____)
L = ( 2 x 7 x F )
C
Similarly using the capacitance –resistance oscillator configuration ,.the output Frequency can be calculated for known values of R and C. several formulae exist for this calcUlation and the one used in this application is:
F = ____1____
7 x R x C
from which the value for C can be calculated if R and F are known:
C = 1___
7 x R x F
cont……………
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