Test Instrument Buffer
DC version
AC Version
LM358
Goal: High impedance Interface for both meter movements and multimeters.
Inexpensive buffer device affording VTVM or FET Meter Capability.
Input Impedance: 1GΩ?
Schematic Capture Schemeit
Spice Lt SPice
Physical Test XP
PCB Route
Easy Eda
Current meter movement available 200ua full scale.
Concept Drawing
Audio / Log taper.
Could use 1/5 value pot on wiper to trim.
47k is to large of a resistor on a 100k pot if you want to emulate an
audio taper, it should be more like 10k to 20k. More info here: Potentiometers (Beginners' Guide to Pots)
Thank you for this information. I went with the 1/5 value resistor and got good results with my linear pot.
Put 1/5 value resistor on wiper to ground. .
Pots
Build into square box.
Veleman Page
Veleman Preamp $13.95 Amazon
Manual
High
Impedance input stage Buffer Multimeter Test
Amplifier 741 (10 for $4.29 / 0.43 ea. )
LF411 $1.40(higher
impedance) Metal Can version LM741EH $7.50
Lm 358 20/ $3.49 .17 fuse more expensive than device.
LM358 INFO
Online Conceptualization.
Circuits today.
$400-$2258
$275 used
$11 for AD8244\
60 IC sockets $9
Socketed Board
Adjustable Gain
Toggle Switches for gain.
pots for adjusting.
Use analog meter on front.
Use heathkit as basis.
Rectifier Circuit for Plane meter.
Opamp buffers
LM358 Dual Op-Amp IC features and specifications
- Integrated with two Op-Amps in a single package
- Wide power supply Range
- Singe supply – 3V to 32V
- Dual supply – ±1.5V to ±16V
- Low Supply current – 700uA
- Single supply for two op-amps enables reliable operation
- Short circuit protected outputs
- Operating ambient temperature – 0˚C to 70˚C
- Soldering pin temperature – 260 ˚C (for 10 seconds – prescribed)
- Available packages: TO-99, CDIP, DSBGA, SOIC, PDIP, DSBGA
Link for below circuit
Link for the below circuit.
Voltage measurement Methods
This type of amplifier circuit has a voltage gain of 1
and an input impedance of several hundred million ohms.
2 megohm input imedance. for 741
Article for 741 Ac meter.
This circuit uses the LM358 OPAMP in a "Voltage Follower "
configuration.
Several hunred million Ohm Buffer Amp.
Protection circuit.
Lm 358 20/ $3.49 .17 fuse more expensive than device.
Dip Socket
http://www.radanpro.com/Radan2400/TestShematics/high%20resistance%20voltmeter%20circuit%20diagram.htm
Pricey:
https://www.analog.com/en/technical-articles/high-voltage-cmos-amplifier-enables-high-impedance-sensing-with-a-single-ic.html#
http://www.skillbank.co.uk/arduino/measure2.htm
TL082
https://www.allaboutcircuits.com/textbook/experiments/chpt-6/high-impedance-voltmeter/
Link for below
