Capacitors are vital components in electronics, but sometimes they are broken, or the value printed on the cap has become unreadable. Because my multi-meter does not have a capacitance measurement, I decided to make one!

The principle of measuring capacitance is quite simple. The voltage of a capacitor charging through a resistor increases with time T. The time it takes to reach a certain voltage, is related to the values of the resistor and capacitor. In this project, we’ll use a 555 timer circuit as a monostable multivibrator. If that sounds like some dark magic to you, don’t worry, it’s quite straightforward. I’ll refer to the the Wikipedia page for the details, as we’ll focus on the things we really need: the schematic and formula. The time in which the capacitor C charges through the resistor R is given by: T = ln(3) x R x C = 1.1 RC. If we know the value of the resistor and the time, we can calculate the capacitance: C = T / 1.1R.

Electronics DIY published a new build, the Curious C-beeper:

Curious C-Beeper is a fun to build little probe that can be used to quickly detect the capacity of capacitors in pF nF range, test their stability with temperature changes, find broken wires, locate wires, trace wires on PCBs, and to locate live wires behind the walls without touching them. The circuit uses three transistors to make a most unusual capacitance beeper probe. When a capacitor is touched to the probe, the probe beeps at a frequency that varies with capacitance. The frequency change is so steep with capacitance that tiny capacitors may be precisely matched or an exact fixed value may be selected to replace a trimmer in a prototype.

I had a bunch of random inductors in some random drawers and I wanted to know what values they were. These values are quite often not obvious by looking at the device. Colour codes for old ones were not standardized and some of the coloured rings on inductors can be faded or discoloured so that its impossible to tell what they are. Others may be unmarked and any that are hand-wound are just guess work without a meter. So I decided to make an inductance and capacitance meter which would be fairly accurate and work over several decades of value from a few nano-Henries to a few milli-Henries and also from a few pico-farads to about a micro-farad (hopefully). Sounded easy – what could go wrong?

This Design Idea describes a simple two-chip CMOS circuit that can sort capacitors into 20 bins over a wide range (100pF to 1μF), using 10 LEDs to display the value range. The circuit is power efficient and can be run using two CR2032 cells. As such, it can be built into a handheld probe. by Raju Baddi

What is the actual capacitance of typical breadboard contacts?

It’s not in the datasheet, so Dave decides to measure it. It is well know that breadboards are not suitable for high frequency work due to the stray capacitance between contacts, but how bad is it really?

Although most people probably haven’t given it much thought, the invention of the coaxial cable was probably one of the most important discoveries ever made. Telecommunications and radio broadcasting would not exist as they are today without the invention of the coaxial cable.

Coaxial cables first started to appear in various applications back in the 30’s as a need developed for more efficient cabling systems with less interference. As more coaxial cables were used, standardised versions became available. Probably the most important parameter used in coaxial cabling is the characteristic impedance.

This is the main electrical characteristic that determines the level of power transfer and attenuation along the cable length, and also controls the amount of reflected and standing waves. Any type of coaxial cable is typically chosen based on the characteristic impedance. The main consideration is that impedance levels should match both at the transmitting and receiving end.

Although there are many standard impedances levels, the most common ones by far are the 50Ω and 75Ω impedances. These two standards are used for most coaxial cable applications, but other standards are also available in lesser quantities. For ordinary signal and data transmission applications, the cable that almost always chosen is the 50Ω type, while the 75Ω type is almost exclusively used for video signal and high-frequency RF applications, such as VHF (Very High Frequency) and UHF (Ultra High Frequency).

The need for high capacitance can be fulfilled via the use of a Capacitance Multiplier. The operational amplifier circuit is used as a capacitance multiplier in such a way that multiple small physical capacitances are combined in the integrated circuit technology to yield a large overall capacitance. The aim is often to multiply the original capacitance value hundreds and thousands of times. For example, a capacitor of 10 pF capacitance could be upgraded by the use of capacitance multiplier to behave like a 100 nF capacitor.

Construction of Capacitance Multiplier Circuits:

The circuit construction of a capacitance multiplier is quite simple. Two operational amplifiers, two resistors and a capacitor are used. The second operational amplifier is an inverted amplifier. A voltage source connected to the first operational amplifier will make the amplifier operate as a voltage follower. The circuit will produce a capacitance via the load imposition created by the second amplifier acting as an inverted amplifier. The produced capacitance is isolated from the circuit with the help of voltage follower. In this way, no current flows into the input terminals of the operational amplifier – the input current will flow through the feedback capacitor of the capacitance multiplier circuit.

How Are Multiple Capacitances Produced Using An Operational Amplifier Circuit?

Critical to production of effective capacitance is the selection of good resistance values for the two resistors in the multiplier circuit.The effective capacitance produced will be the capacitance between the input terminal of the operational amplifier and the ground. This effective capacitance will be the multiple of the physical capacitance ‘C’ of the operational amplifier circuit being used as a capacitance multiplier. There is an option to limit the size of this effective capacitance by the use of an inverted output voltage limitation technique. This is a practical approach to limit the size of the effective capacitance.

Relation between Size of Effective Capacitance and Input Voltage:

The capacitance multiplication and the maximum input voltage avoiding saturation state in the operational amplifier are inversely proportional to one other. Effectively, the larger the size of the effective capacitance, the smaller the input voltage into the input terminals of the operational amplifier. Using a similar technique, a resistance multiplier circuit can also be implemented by configuring an operational amplifier circuit. Furthermore, the same operational amplifier circuit can also be designed to simulate inductance.

Raj from Embedded Lab describes in his latest tutorial the theory of a very basic digital capacitance meter and its implementation using a PIC microcontroller. It is based on the principle of charging a capacitor through a series resistor and determine the time required to charge it to a known voltage. The built-in analog comparator and Timer2 modules are used in this process. The meter can measure capacitance from 1nF to 99.99 uF.

Digital Capacitance Meter using a PIC Microcontroller – [Link]

An LCR meter is an extremely useful device for measuring three basic impedance elements, namely, Inductance (L), Capacitance (C), and Resistance (R). Recently, I got a TENMA 72-8155 digital LCR meter from Newark for review. I was very excited to receive it as I didn’t have a dedicated LCR meter in my home lab. Here’s my quick review of this product.

This is very accurate home made LC inductance/capacitance meter built with very common components which are very easy to find all around . The range of this LC Meter is extremely good at measuring very low value of capacitance and inductance.

LC Meter’s Inductance Measurement Ranges:

10nH – 1000nH

1uH – 1000uH

1mH – 100mH

LC Meter’s Capacitance Measurement Ranges:

0.1pF – 1000pF

1nF – 900nF

Very Accurate LC inductance / Capacitance Meter – [Link]

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