Capacitance to voltage meter


Posted on Aug 23, 2012

Timer Ul operates as a free-running oscillator at 60 Hz, providing trigger pulses to timer U2 which operates in the monostable mode. Resistor Rl is fixed and capacitor Cx is the capacitor being measured. While the output of U2 is 60 Hz, the duty cycle depends on the value of Cx. U3 is a combination low-pass filter and unity-gain follower whose dc voltage output is the time-averaged amplitude of the output pulses of U2, as shown in the timing diagram.


Capacitance to voltage meter
Click here to download the full size of the above Circuit.

The diagram shows when the value of Cx is small the duty cycle is relatively low. The output pulses are narrow and produce a lower average dc voltage level at the output of U3. As the capacitance value of Cx increases, the duty cycle increases making the output pulses at U2 wider and the average dc level output at U3 increases. The graph illustrates capacitance values of 0.01 ?Â¥ to 0.1 ?Â¥ plotted against the output voltage of U3. Notice the excellent linearity and direct one-to-one scale calibration of the meter. If this does not occur the 100 k ohm resistor, Rl, can be replaced with a potentiometer which can be adjusted to the proper value for the meter being used.




Leave Comment

characters left:

New Circuits

.

 


Popular Circuits

Ultra Low Power LCD Indicator
Audio Fader
Dancing LEDs
Converter Circuit 6
quad power supply for hybrid amplifier
High Quality Intercom circuit
IR Headset Circuit with headphone Transmitter and Receiver diagram
own capacitor
non inverting opamp butterworth filter
Crank Doorbell Circuit Schematic
74S124 High Frequency VCO with Varactor
JFET-Bipolar Cascode
2Y-2Y-2Y-connected three-speed motor contactor control circuit



Top