Magnet coil cores, demagnetization power and Lenz delay.

[MarkE]

This link takes you to the Aeroelectric web site. You need to type Ohm meter in the google search engine, then click on the link to get the PDF. This is a booster pack that adds power to a DMM:

www.aeroelectric.com/.../LowOhmsAdapter_3.pdf

The key to interfacing the boosted DMM readout to the Op Amp is the "Zener Diode".

There is no "boost".  It is a regulated current source packaged with leads to make a 4 wire Kelvin connection.  The best part about the circuit is that it only draws power from the batteries when the probes connect across a resistance.  The range of resistances that one can read depends on how low one's voltmeter can go and how much current one can supply from their current source.  For garden variety DMMs where the lowest scale is 200 Ohms, a device like this can extend that way down.  A 100mA source will make the 200mV range on a DMM read 2 Ohms full scale.  Just be sure that circuit under test can tolerate 100mA.

[synchro1]

Simple Variable Zener Diode:

There are several variable zener diodes available in IC market, but in Sri Lanka it is difficult to obtain variable zener diodes. (For example LM431) So I build this circuit to get the functionality of Variable Zener diode. This circuit is based on two transistors and for Q1 you can use any general purpose NPN transistor and for Q2 use any general purpose PNP transistor.

The LM431 is easier to find in America. Nice circuit though!

[MarkE]

Simple Variable Zener Diode:

There are several variable zener diodes available in IC market, but in Sri Lanka it is difficult to obtain variable zener diodes. (For example LM431) So I build this circuit to get the functionality of Variable Zener diode. This circuit is based on two transistors and for Q1 you can use any general purpose NPN transistor and for Q2 use any general purpose PNP transistor.

The LM431 is easier to find in America. Nice circuit though!

Can't you order parts from China?  The circuit that you show is not temperature stable.  You could fix the circuit with a thermistor and a couple of resistors, or just buy any voltage reference.  The TL431 is over 35 years old.  You should be able to obtain one as easily as any Op-Amp or garden variety transistor.

[synchro1]

Can't you order parts from China?  The circuit that you show is not temperature stable.  You could fix the circuit with a thermistor and a couple of resistors, or just buy any voltage reference.  The TL431 is over 35 years old.  You should be able to obtain one as easily as any Op-Amp or garden variety transistor.

My Television's 35 years old and works fine without junk parts from China or smart alek advice from know it all punks. There's always some kind of stupid ass problem our of you. It's always some sort of trouble you make to sound as smart as smart can be. You're just a blood sucking arachnid.

[MarkE]

My Television's 35 years old and works fine without junk parts from China or smart alek advice from know it all punks. There's always some kind of stupid ass problem our of you. It's always some sort of trouble you make to sound as smart as smart can be. You're just a blood sucking arachnid.

Unless you are cannibalizing your TV for parts, your TV is rather irrelevant to what will get you a decent adjustable voltage reference.  Your simple circuit doesn't have any form of temperature compensation/stabilization.  TL431's are ubiquitous and almost as cheap as one or two transistors.