Many thanks.

+Lawrence Kesteloot Thank you for your kind comments.

+Dino Papas Thanks Dino.

Thank you.

Glad you enjoyed it. Thanks.

Many thanks. Glad to hear you find it helpful. Regards, Louis

+Mighty Astro Thanks for your comments.

Thank you. I will be posting an update on this project soon as a PCB is now available for this project.

Thanks George.

Thanks for your comment.

Glad you found this project useful.

+Mark Garth Thanks Mark.

+William Culver Thanks.

+Piotr Hołowicz Thanks. A full SMD version should be quite neat.

+Alexander Brevig Thanks Alexander.

+search4robfen Thanks.

+Милан Младеновић Thanks.

Thanks. I will be uploading an update on this project soon using a smaller PCB and some improvements to the circuit.

+Robert Calk Jr. Thanks Robert.

+Steve Rodgers Thanks for the comments and info.

+Asniex Asniex Thanks for your comments. You must have read my mind. My next video project will be on designing and making a precision 6½ Millivolt meter with auto calibration option at low cost suitable for the hobbyist. I have been busy of late but hope to complete this video in the next few days.

That really chuckin awesome

Glad you found it helpful.

Thanks.

Thanks Seyed.

+Yann Kitson You're welcome.

Thanks.

+Yash Kudale Thanks for your comments. Good point about the design process. Also I have been considering a video on op amps. May be something I can do when I have time.

+su pyrow Thanks for the tip on "Front Panel Designer".

Thanks Steve for your valid comment. The one I use are quite good quality so they seem to have been OK so far. Regards, Louis

+Adil Malim Thanks.

Thanks :)

+David Az Thanks for your comments.

Thanks.

+Mike Novo Thanks for the comment. In this circuit I am using the INA106 configured as a Differential Amplifier the gain is therefore x10. We are using both the + and - inputs and therefore the output is Vout=10(Plus Input - Negative Input). If you were to configure the INA106 as a non inverting buffer then the gain would be x11 but in that case the negative input pin (pin 2) would be grounded. Hope this clarifies the point.

Of course. I see that now. Thanks!

Thanks for the comment. Nice idea but I think it may be costly to fully copy a Keithley 2000. Regards, Louis

+First2ner Thanks for your good comments. I have found using a good quality resistor either a 0.1 ohm or 1 ohm at 0.1% tolerance, you can use that to set the reading and that should give you 100 mA, at that tolerance level. I take your point about the 100mA with regards heating but I have found that in practice with resistances below 1 ohm it has little effect and usually you are testing a resistance for just a few seconds (for example a 0.1 ohm resistor at 100mA will only needs to dissipate 1 milli watt of power).

+First2ner This is why the resistors are in parallel. 8x 1 watt resistors in parallel is a max rating on 8 watts. 1mW requirement means it's not even an issue. Awesome

+ToltecMerc Thanks. Yes you are right their is a trimmer inside the panel meter, I will give it a try.

+TheStuffMade Thanks for your comments. Thermal EMF compensation is really only needed at much lower resistance readings in the low micro ohms and below. Also if you wanted to check such low resistance readings you would also need to screen all the input leads to stop pick up of noise.

Thanks.

+The mad Engineer Thanks for your comments.

Thanks Jake for your comment. The reason I have tended to use battery operation for most of my projects is to make it easier for the hobbyist and amateur who may not feel comfortable with building mains (240V AC) power supplies and the dangers that can pose if you are not familiar with working with mains AC. All of the projects could also be powered from a mains power supply if you wish. You could either build your own or buy an off the shelf mains power pack. I have also designed and built valve amplifiers operating from a mains power supply and high DC voltages. If there is an interest in this I could do some projects/tutorials on building valve amplifiers and point out the safety issues. Regards, Louis

Thanks for the reply Louis. I've found myself building power supplies for basic experiments, mostly working with guitar amps and op amp preamplifier circuits. I have come across the limitation of my tools. Your tutorials have helped me see how I can connect the dots and fill the gap in my lab. I really appreciate how you break down exactly how each item works in the circuit and why. I feel like I can use individual elements and the underlying principles to create designs of my own. I have very limited means, and far too much time on my hands after an accident left me disabled back in February 2014. I went from building hotrods to electronics to fill my time. I am trying to apply what I learned from autobody and engine building -buying parts is fun, but collecting the tools and skills used to make parts is the real secret to success. I already had the basic tools like a decent multimeter and hand tools. Since getting hurt, I've been fortunate enough to pick up a second hand Rigol digital oscilloscope and a good soldering station. I also have a local thrift store that lets me pick up any broken electronics that they throw out along with the gigantic tangled mess of wires and power supplies they throw out regularly. I've collected a lot of junk so far. That gives me access to almost any jellybean components found in most consumer electronics along with any common wall wart and switch mode power supply made. This in turn forces me to learn to test everything from shunt resistors, zener diodes, capacitor ESR, and transistor curves, all of which I'm currently trying to wrap my head around. It can be time consuming to learn this way but time is one thing I have too much of. I really do appreciate your projects and I want to build a few. Hopefully my permanent disability goes through soon, but until then I'm using the building blocks of your circuits to understand circuit function and to build a rudimentary version on my own using discrete components. I have a shopping list of parts to build your 6.5 digit millivolt meter, your milliohm meter, and I will probably try your function generator in the future as well. I'm currently working on an adjustable dual polarity tracking power supply using a lm317 and an op amp, a discrete floating adjustable power supply with current limiting, and a simple audio probe/function generator/crystal tester using discrete components and basic op amps. I am interested in expanding my knowledge and experience, but I don't even know what a valve amplifier is used for. I'm very linear with my learning curve. When I come across a problem I can't solve I want to understand everything related to it. For instance, my inability to measure current shunts, lead me to understanding how a 4 wire kelvin connection works, differential amplification, and a more broad understanding of the need for accurate current source circuits. I also picked up a basic understanding of wire resistance and capacitance and it's impedance matching effects, reflected waves and their measurement using a Schmitt Trigger to measure a coax length, and I even learned a bit about antennas and built my first. Some of that came from your milliohm meter tutorial, and some of that is from several other sources. I learn by exploring problems and solutions like this. My next experiment will be to try to build a differential amplifier using transistors in a long tailed pair and see how that compares to parts of your milliohm meter circuit. I found a good tutorial on a long tailed pair from Alan on A2AEW where he explained how to build an adjustable triangle waveform generator. I will try to expand on his lesson by trying to figure out how to implement some feed back into the circuit, but this subject is on the foggy edge of my understanding and ability. The sad thing is that I have an old 80's broken Programmable Power Supply from Fluke and one that powers up from HP. Both were given to me, and are enormous rack mounted units. I haven't been able to figure out how to interface with the HP and make it work. I much prefer analog electronics to programming at the moment. The timing of bits and everything involved to get the thing running (cheaply) is mind boggling to me, and I keep putting it off until I understand electronics better. The fluke unit, however, I can't find enough information on, as no one appears to have a full schematic. It was missing capacitors on a couple of boards but I have no way of figuring out what they were. It has lots of interesting parts including a nice precision voltage reference, a massive transformer and tons of discrete matched and precision components, but without a schematic I stare at it for hours in perplexity... One day. Anyways, sorry if my ramblings are unwelcome. They could be considered a marker of where one odd member of your audience is in terms of understanding and ability. I'm probably in over my head with most of your content, but I have a tendency of banging my head against the wall of knowledge until I make my own doors. Thanks, -Jake.

Hi Jake, Looks like you are having an interesting journey learning electronics. All the best, Louis

+capriracer351 Thanks. I have found that using 100mA current source to be the best option as you are able to get a better voltage reading and therefore a higher degree of accuracy. Some commercially available Milliohm meters on the market do use 10mA source current but in practice I have found their results to be poor on very low resistance readings below 20 milliohms. The higher the current used the better the accuracy of the results. Of course there may be some difficulties in providing a high value very accurate constant current, but today with the Linear Technology IC LT3092 this is relatively easy up to a maximum current of 200mA. At these levels heat is not really an issue. So to summaries I would recommend you stick with the 100mA.

+MrMonomonster Thanks. The panel meter I used on the project proved to be accurate up to 0.1mV reading. So it was fine what the project set out to do. This panel meters are a little more expensive than some others costing around £8, but worth it.

Thanks. Yes it could be used to measure low resistance of motor winding if you wish.

Hi, I think you would have to make minor changes to the PCB. The INA106 Reference pin is pin1 but on the INA131 it is pin 5. Pins 1 and 8 of the INA131 should be left unconnected. Other than that all the other pin connections are the same. So I think if you make the pin connection changes to the PCB it should work. It would be interesting to see how it functions with the INA131. You would also have to take in to account change to voltage reading on meter. To maintain the same gain error as the INA106 you should use the INA131BP version. If you try it let me know how you get on. Good luck.