Build Your Precision Millivoltmeter Circuit Diagram

This circuit measures from 10mV to 50V RMS across eight different settings.

Simply connect it to your Avo-meter, configured for a 50uA current range.

Circuit Diagram

Components:

R1 909K Ohm, a 1/2Watt, 1% Metal Oxide Resistor
R2 90.09K Ohm, a 1/2Watt, 1% Metal Oxide Resistor
R3 9.009K Ohm, a 1/2Watt, 1% Metal Oxide Resistor
R4 1.001K Ohm, a 1/2Watt, 1% Metal Oxide Resistor
R5 100K Ohm, a 1/4Watt Resistor
R6 2.00M Ohm, a 1/4Watt Resistor
R7 82.0K Ohm, a 1/4Watt Resistor
R8 12.0K Ohm, a 1/4Watt Resistor
R9 1.000K Ohm, a 1/4Watt Resistor
R10 3.300K Ohm, a 1/4Watt Resistor
R11 200R Ohm, a 1/2Watt Trimmer Cermet
C1 330nF, 63V Polyester Capacitor
C2, C3 100uF, 25V Electrolytic Capacitor
C4 220uF, 25V Electrolytic Capacitor
C5 33pF, 63V Polystyrene Capacitor
C6 2.20uF, 63V Electrolytic Capacitor
D1-D4 1N4148, 75V, 150mA Diodes
IC1 CA3140 Operational Amplifier (Op-amp)
IC2 CA3130 Operational Amplifier (Op-amp)
SW1 2-pole, 5-way rotary switch
SW2 SPDT switch
J1 RCA audio input socket
J2, J3 4mm. output sockets
B1 9V PP3 Battery
Clip for PP3 Battery

Notes:

Connect J2 and J3 to your Avo-meter, configured for a 50uA current range
Switching SW2 multiplies the four input ranges by a factor of 5
The total available range is: 10mV, 50mV, 100mV, 500mV, 1V, 5V, 10V, 50V
To calibrate R11, set it to read 1V within the 1V range, using a sine wave input of 1V at 1KHz
Verify the reading against another known precision millivoltmeter or by observing the waveform on an oscilloscope – the oscilloscope reading should display a sine wave with a peak-to-peak amplitude of 2.828V
The frequency response is flat across the 20Hz to 20KHz range
If you encounter difficulty in locating the exact resistor values for R1, R2, R3, and R4, you can employ the following method:

R1 = 10M Ohm + 1M Ohm in parallel
R2 = 1M Ohm + 100K Ohm in parallel
R3 = 100K Ohm + 10K Ohm in parallel
R4 = 1.001K Ohm + 6.8K Ohm in parallel
All resistors possess a 1% tolerance

Operational Amplifiers (ICs):

Operational Amplifiers

The CA3140 and CA3130 are both widely utilized integrated circuits, specifically designed as operational amplifiers. These devices are fundamental building blocks in many analog circuits, enabling amplification, filtering, and signal conditioning. They are characterized by their high gain, input impedance, and low offset voltage, making them suitable for a broad range of applications, from audio preamplifiers to instrumentation circuits. Their versatility and readily available pinouts contribute to their popularity in electronic design.

author: RED Free Circuit Designs
circuit from http://www.redcircuits.com/