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

Battery charger
Light isolated solid state power relay circuits
Audio-controlled lamp
100W Inverter
3 volts car adapter using lt1074ct
Scheme research and design of the ultrasonic range measurement system
mosfet Turning a microcontroller on with a flip flop
microphone CAD equitek E100
digitally controlled oscillator dco design
Sound Level Indicator
Complete SS Laser Power Supply Schematics
Inductorless 5V to -5V Converter
Frequency meter with 10Hz to 2MHz
ARM module optical fingerprint recognition circuit schematic
Hydraulic oil Automotive LED Alarm SL322C schematic
Flashing light indicates the light switch circuit



Top