# Inductance and capacitance meter adapter for DVM

This device is an addon to a digital or analog voltmeter. The device can measure inductance in the 100μH...1H range, capacitance in the 100pF to 1μF range, and it also produces a set of frequencies 100 Hz, 1 kHz, 10 kHz, 100 kHz, 1 MHz.

#### How the circuit works

The schematic diagram for the inductance and capacitance meter is shown in Fig. 1. The main part of the circuit is a digital IC CD4011 (CD4001 also can be used instead of IC CD4011). It works as an oscillator whose frequency is determined by the RC components R1..R5 and C1..C5 in feedback circuits. A two deck rotary switch S1 selects one of five measurement ranges. The transistor Q1 is used to amplify the signal to provide sufficient current through potentiometer R8 and a load circuit. The signal at the collector of Q1 has 50% duty cycle.

Fig. 1. Simple adapter circuit for DVM

The switch S2 is in position "L"

DD1 - CD4011; DA1 - 7806; Q1 - 2N2907; VD1, VD2 - 1N34A;
C1 - 100pF; C2 - 1nF; C3 - 10nF; C4 - 0.1μF; C5 - 1μF;
C6 - 1μF; C7 - 1nF; C8, C9, C10 - 100μF;
R1..R5 - 10K; R6, R7 - 470Ω;
R8 - 470Ω; R9 - 1K; R10 - 3.3K.

A switch S2 is used to configure the measurement circuit. When it switched into position "L", the measurement circuit operates as an inductance meter, see the Fig. 2:

Fig. 2. The switch S2 is in position "L"

This circuit provides DC output voltage on the clamps X6, X7, and this voltage is directly proportional to the inductance of Lx. The voltage is negative. The source of the voltage is negative pulses across the inductance Lx.

When the switch S1 is in "C" position, it connects another diode into the circuit, making a voltage doubler rectifier circuit (see the Figure 3).

Fig. 3. The switch S2 is in position "C"

In this case, the pulses of current through the capacitor Cx are proportional to its capacity.

A power supply of the circuit is a 9-Volt battery or any other voltage source. The 7806 voltage regulator provides 6-Volts stabilized voltage for the circuit.