Electronic Circuits and electronic circuits, electronic schematics plus an extensive resource for hobbyists, inventors and engineers

DiscoverCircuits.com, has 30,000+ electronic circuits, cross-referenced
into 500+ categories.    We have searched the web to help you find quick design ideas.
We make every effort to link to material posted by the designer. 
Please let us if you would like us to link to or post your design.

HOME Schematics Discover Forum Hobby Corner Dave's Circuits Electronic Resources Contact Info
Imagineering Ezine    Discover Solar Energy Dave Johnson & Associates Faraday Touch Switches


 
[H-Corner/i-TOP-wAD.htm]

DiscoverCircuits.com -- Hobby Corner
Last Updated on: Tuesday, April 01, 2014 04:34 AM

Hobby Circuits' Category List

The contents & graphics of Discovercircuits.com are copyright protected.
LINKING to Dave's circuits is permitted but DO NOT COPY any files to your WEB SITE server



Precision Low Capacitance Meter -- July 8, 2008
This circuit was originally designed to measure the volume of the fluid inside a 10cc syringe.  It used two copper foil strips attached to the outside barrel of the syringe.  The fluid between the two copper strips increases the capacitance. As the fluid volume decreased, the capacitance also decreased.  With the circuit shown below, it is possible to calibrate the circuit, so the voltage produced is proportional to the fluid volume inside the syringe. 

With the values shown, the circuit produces a 5v DC output, when the 10cc syringe is full. It is possible to measure the fluid volume to a resolution of 0.01cc.  The circuit can also be adjusted to produce a 5v DC output voltage for a capacitance of 10 picofarads to a solution of 0.01 picofarads.

The circuit measures the unknown capacitance by applying a clean 20KHz 5v peak to peak triangle signal to the capacitor.  The current routed through the capacitance is sent to a current to voltage converter. The voltage that emerges is therefore a 20KHz square wave signal, whose amplitude is proportional to the capacitance.  The signalís peak amplitude is rectified and filtered to produce a DC voltage. Additional op amps provide a means to adjust the zero and span of the circuit, so a fixed change of capacitance will produce a known voltage change.  A fixed 9v DC supply powers the complete circuit.
 

Click on Drawing Below to view PDF version of Schematic

More 

Capacitance Switches    Fluid Level Monitor

Hobby Circuits' Category List
eMail David A. Johnson, P.E. about this circuit

[H-Corner/ads/i-HC-boombox_adsense.htm]


HOME Schematics Discover Forum Hobby Corner Dave's Circuits Electronic Resources Contact Info


 About Us   |  Advertise on DiscoverCircuits.com   |   Report Broken Links  |    Link to DiscoverCircuits.com  |    Privacy Policy

Copyright  2002 - 2013 David A. Johnson & Associates.  All Rights reserved. 
 Linking is ALLOWED but COPYING any content or graphics to your web site is EXPRESSLY PROHIBITED.