Voltase hobby: meter

Tuesday, November 11, 2014

Loudspeaker Impedance Meter

Also suitable for Headphones Operates in conjunction with a DVM

A simple Impedance Meter can be useful to measure the actual impedance a loudspeaker or headphone is presenting @ 1kHz standard frequency. The circuit, designed on request, relies on an earlier design (Spot-frequency Sine wave Generator) to obtain a stable, low distortion 1kHz sine wave avoiding the use of thermistors, bulbs or any special amplitude-limiting device. The sine wave output, after some amplitude setting obtained by means of P1, is sent to the device under measurement through a resistor.

A regulated supply is necessary to obtain a stable output waveform. D1 and D2 force IC1 to deliver 6.2V output instead of the nominal 5V. The measurement is done in two stages: as a constant current supply of the device under test is necessary, this can be set at first by adjusting P1 and measured across the series resistor (R7 or R8, depending on the impedance value to be measured); then, the meter is switched across the device under test and the actual impedance will be read directly on the meter display.

Circuit diagram:

Loudspeaker Impedance Meter Circuit Diagram

Parts:

P1_______________4K7 Linear Potentiometer
R1______________12K 1/4W Resistor
R2_______________2K2 1/4W Resistor
R3_______________1K 1/2W Trimmer (Cermet)
R4_______________1K5 1/4W Resistor
R5_______________4K7 1/4W Resistor
R6_______________3K3 1/4W Resistor
R7_____________100R 1/4W Resistor (See Notes)
R8_______________1K 1/4W Resistor (See Notes)
R9_______________1K 1/4W Resistor (Optional)
C1______________22nF 63V Polyester Capacitor
C2_____________330nF 63V Polyester Capacitor
C3______________22µF 25V Electrolytic Capacitor
D1,D2_________1N4148 75V 150mA Diodes
D3_______________3mm Red LED (Optional)
Q1,Q2,Q3_______BC550C 45V 100mA Low noise High gain NPN Transistors
IC1____________78L05 5V 100mA Regulator IC
SW1,SW2_________SPDT Toggle or Slider Switches
SW3_____________SPST Toggle or Slider Switch
B1________________9V PP3 Battery

Clip for PP3 Battery

Circuit set-up using an oscilloscope:

Connect the oscilloscope in place of the DVM and rotate P1 fully clockwise.
Short the speaker output and adjust R3 to obtain a sine wave of about 2.2V peak-to-peak amplitude.

"By ear" circuit set-up:

Connect a small loudspeaker or one of the two earpieces forming a pair of headphones to the circuit output and rotate P1 to obtain a moderate output sound level.

Carefully adjust R3 until the output sound will stop; then turn back the trimmer very slowly and stop adjusting immediately when the sound will start again.

Measurement:

Connect a Digital Voltage Meter set to 200mV ac range to the DVM output terminals
Connect the device under test to the Speaker terminals
Switch SW1 in the position towards R7 if the impedance value to be measured is below 100 Ohm or towards R8 if above
With SW2 in the "Set" position power-on the circuit by means of SW3
Adjust P1 in order to read exactly 100.0mV on the DVM display
Switch SW2 in the "Measure" position and read directly the loudspeaker or headphones impedance value on the DVM display, e.g. 8.5mV = 8.5 Ohm
Please note that when measuring devices with impedance values above 100 Ohm (SW1 set towards R8), the decimal point in the DVM reading must be ignored. E.g. if the display shows 70.5mV, the impedance will be 705 Ohm

Notes:

For very precise measurements use 1% or 2% tolerance resistors for R7 and R8.
D3 LED pilot light and its current limiting resistor R9 are optional.

Thursday, October 2, 2014

Simple Accurate Capacitance Meter Circuit Diagram

ln this capacitance meter, the value of a capacitor is determined by giving it the same charge as a reference capacitance and then comparing the voltages across them.

This relies on the formula C = O/V where C is the capacitance in Farads, O is the charge in Coulombs and V is the voltage in volts. lf therefore two capacitances have equal charges, their values can be calculated when the voltages across them are known. Two circuits ensure that reference capacitor Cr and the capacitor to be measured, CX, are charged equally. The circuit for Cr consists of C2, Di and T1 and that for CX of C3, D2 and T3. Each time the output of gate N2 rises, the charges of capacitors C2 and C3 are transferred to Cr and CX { by trer:cFstorsT1 and T3 respectively.

When the output of N2 drops, C2 and C3 recharge via diodes D1 and D2. Gate N2 is controlled by astable multivibrator N1 which operates at a frequency of about 2 kHz: Cr and CX are therefore charged at that frequency. The voltage across Cy is compared by IC2 with a reference voltage derived from the power supply via R3/R4. When the voltage across Cr exceeds the reference voltage, com- parator IC2 inverts which inhibits N2 and causes N3 to light LED D3. The charges on Cr and CX are now equal and the meter indicates by how much the voltage across CX differs from that across Cr. Buffer lC3 presents a very high load impedance to CX. Pressing reset button S1 causes both Cr and CX to discharge via T2 and T4 respectively, after which the charging process restarts and the circuit is ready for the next measurement. The meter is calibrated by using two identical 10 nF capacitors for Cr and CX. Press the reset button and, when the LED lights, adjust preset P1 to give a meter reading of exactly one tenth of full scale deflection (fsd).

That reading corresponds to 1 x Cr. lf, therefore, Cr = 100 nF and CX = 470 nF, the meter will read 0.47 of fsd. To ensure a sufficient number of charging cycles during a measure- ment, Cr and CX should not be smaller than 4.7nF. To measure smaller values, capacitors C2 and C3 will have to be reduced. For instance to enable a capacitor of 470 pF to be measured, C2 and C3 have to be T0. . . 20 pF. The circuit is reason- ably accurate for values of CX up to 100 pl:. Above that value the measurement will be affected by leakage currents. To measure capaci- tors of up to 100 pF, the values of C2 and C3 should be increased to 1 AF. Current consumption is minimal so that a 9 V battery is an adequate power supply.

Tuesday, September 16, 2014

VU Meter 5 with UAA180

This circuit of measurement of level uses the UAA180 of SIEMENS and a circuit of rectification of precision, round the IC2B. The calibration has become in steps 3db from the one Led in the other, ensuring, a very good rate of precision, in the measurement of entering acoustic signals. The Led can be square, thus when they are placed the one by in the other, they give the picture of bar, without space. VU Meter 5 with UAA180 Circuit diagram: Parts List: R1= 47Kohm
R2= 1Mohm
R3= 33Kohm
R4= 10Kohm
R5= 220ohm
R6-9=390ohm
R7=2.2K ohm
R8-10=330Kohm
R11=180Kohm
C1= 47uF 25V
C2-4=47nF 100V
C3=2.2uF 25V
D1....8= LED GREEN
D9-10= LED YELLOW
D11-12= LED RED
D13....17= 1N4148
IC1= UAA180
IC2= TL072

[Link]

Thursday, September 4, 2014

Simple Meter Impedance Speaker Wiring diagram Schematic

A simple impedance meter can be useful to measure the actual impedance of a speaker or headset, ideal for anyone working with sound, making and repairing speakers. This impedance meter works in conjunction with a multimeter or oscilloscope to measure the impedance.

Meter Impedance Speaker Circuit Diagram

How to make the measurement of impedance speaker with the multimeter

Connect a digital multimeter to AC voltage in the range of 200mV.
Connect the device under test terminals
SW1 to R7, if the value of the measured impedance is less than 100 ohm R8 or upwards.
With SW2 in the "Set" power-on schema through SW3
Adjust P1 to read exactly 100.0mV the display DVM
Switch SW2 in the "Measure" and read directly from the speaker or headphones impedance value on the display DVM, eg 8.2mV = 8.2 Ohm / 80.1mV = 80.1 Ohm

How to make the measurement of impedance speaker with the oscilloscope:

Connect the oscilloscope instead of DVM (multimeter) and turn P1 fully clockwise.
Short the output speaker and adjust R3 to get a sine wave amplitude of about 2.2V peak-to-peak.
How to make the impedance measurement Speaker "By ear"

Connect a small speaker or headphones, forming a pair of headphones to the output of the schema and turn P1 to obtain a level of sound output moderated. Carefully adjust R3 until the output sound stops, then turn the trimpot to adjust slowly and stop immediately when the sound start again.

List of components

P1 4K7 linear potentiometer
R1 12K 1/4W Resistor
R2 2K2 1/4W Resistor
R3 1K 1/2W Trimmer (cermet)
R4 1K5 1/4W Resistor
4K7 1/4W Resistor R5
R6 3K3 1/4W Resistor
R7 100R 1/4W Resistor (See Notes)
R8 1K 1/4W Resistor (See Notes)
R9 1K 1/4W Resistor (Optional)
22NF 63V Polyester Capacitor C1
C2 330nF 63V Polyester Capacitor
C3 22μF 25V Electrolytic Capacitor
D1, D2 1N4148 75V 150mA Diodes
D3 3mm red LED (Optional)
Q1, Q2, Q3 BC550C 45V 100mA Low noise High gain NPN
IC1 78L05 5V 100mA Regulator IC
SW1, SW2 SPDT Toggle or Slider
SW3 SPST switch or Slider
B1 9V PP3 battery for PP3Clip

Notes:

For very precise measurements using resistors R7 and R8 with 1% or 2% tolerance.
D3 LED pilot and his current limiting resistor R9 are optional.