Scullcom Hobby Electronics #53 - DC Voltage Calibrator Part 1
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- Опубліковано 30 лис 2017
- In this project we will design and build a DC Voltage Calibrator, providing a voltage range from 0 to 10 volts in 1 milli volt steps. The user interface will be a TFT display with touchscreen.
Below are links to version 1 of the software for the Arduino Nano. Also a zip file which contains the schematic, PCB artwork (Version 2) and component layout:
www.scullcom.com/DC_Voltage_Ca...
www.scullcom.com/DC_Voltage_Ca...
Parts List link below:
www.scullcom.com/DC_Voltage_Ca...
Below is a link to my KiCad files for this project:
www.scullcom.com/DC_Voltage_Ca... - Наука та технологія
An exceptionally well presented project. Bundles of information and zero guess work required. Brilliant!
Welcome back! Great to see you're back in the saddle, and new projects coming along. This just made my day!
Hi William, Glad to hear it :-). Nice to be back. Regards, Louis
It great to have you again doing videos... I think you gave us some time to finish the past projects :)
Thanks. Its nice to get back to electronics and a new project. I need to get back in to the swing of things again. Regards, Louis
Nice to see you back, great project and thank you.
Louis- We love your videos and hope you are well. Looking forward to some future updates and wish you the very best!
Glad to see you back again. Great little unit, worth the wait for this one.
Thanks nice to be back. Regards Louis
We all miss you! Hope you'll get more time for your hobby! God luck and wish you lots of health and no more problems!
Amazing, this is exactly what I used looking for to expand my electronics knoweledge, a thoroughly explained design process and process
Good to see back in the lab Louis. This will be an outstanding project to build from start to finish. Thank you.
Thanks Mike. Hope to get Part 2 filmed soon. Regards, Louis
Great return project! Looking forward to Part 2, including how to calibrate the calibrator and exploring future options.
Thanks. I will be working on Part 2 in the next days. Regards, Louis
Thanks again for another awesome opportunity to learn electronics. Opposed to all the other channels trying to explain how the components work, your channel shows what you can with it. This triggers me to dive deeper in to the nitty gritty of electronics. Thanks again
Thanks for your comments. Glad to hear you find it helpful. Regards, Louis
Good to see you back. Thanks for the great projects !
Thanks for you kind comment. Regards, Louis
Love the calibrator project, I can see this one being built by lots of folks. Well done.
Thanks Ian. Its not quite up to the standard of your unit but it may prove adequate for the hobbyist. All the best Louis
Woohoo! A Scullcom video in my subscriptions? Christmas has come early. Glad to see you haven't abandoned making videos.
Thanks. Have a good Christmas. Regards, Louis
WOW Louis, that was a long recess from Scullcom School of Electronics. But, family does come first. I think I can speak for all that we missed you so much. Yes we missed the projects and the videos---but the real truth is we missed YOU. It is so good to see you again. We love you buddy. Have a Merry Christmas and a Happy New Year. I am not sure how you come up with these ideas for projects but I like your way of thinking. Take care Louis. God bless you.
Thanks James. Very nice of you to say. Have a great Christmas :-) Regards, Louis
Good to have you back with new vids, Louis. Looking forward to the next part.
Thanks Peter. Regards, Louis
I think your projects are the better ones to build, they seem to be very accurate and well designed. I had no idea all this stuff was available, I graduated tech school in 2000 and kind of dropped out of the scene for a while. No I wasn't in prison, worse, I lived with my ex. AKA wicked witch of the west
Welcome back! Nice project!
Thanks Tony. Regards Louis
Very nice project. Thanks you very much for sharing all the details with us. Looking forward for part 2.
Thanks for your comment. Regards, Louis
Sir, your voice was just made for explanation of projects. Thank you for explaining things, in a way that I totally understand.
Thanks Timothy for you nice comment. Regards, Louis
It's great to see you again. I will follow this other project. Thanks a lot to share your acknowledge
Thanks for your comment. Regards, Louis
Glad you're back with another great little project. Something to get my teeth into over the Christmas holidays :-)
Thanks for the comment. Hope to get Part 2 of this project done before Christmas. Regards, Louis
Amazing design Louis...
Very glad you’re back. Another great learning project! Good explaination also. Thumbs up!
Thank you :-)
Glad to see you back! thanks for another great project.
Thanks Simon.
Excellent! Your projects just keep getting better. Thank-you for the time and effort you put into your videos, it must be heart-breaking to have to eventually wipe off those white-board diagrams....they are very much appreciated.
Thanks Tom, Yes it is a shame when I have to wipe off some of my drawings. But I hope they help with the explanations :) Regards, Louis
Can’t wait for part 2 of this. Keep up the good work 👍🏼
Thanks.
I'm skipping a couple of past projects for the moment to get to this one, I'm having to build a much more compact workshop, where I'm building almost all home made equipment,because I enjoy the building, I've wanted one of these for sometime, thank you Louis you certainly have your finger on the pulse,I love these projects featuring TFT, screens, and the fact your using normal size parts, the nano and tft are quickly becoming the hobbyists and radio amateurs friend.
73 Paul M0BSW
Hi Paul, Looks like you are going to be busy. This is the first time I have done a project using a TFT touchscreen so it is also a learning process for me to. All the best, regards Louis
~Hello Louis, I like to keep the grey matter busy,, plus I'm learning something everyday,TFT & Oled are very interesting devices although Oled screens of a decent usable size, are still a bit expensive in my view.
Amazing engineer, amazing indeed👌
Thank you :)
great to have you back
Thanks Roland, nice to be back. Regards, Louis
I sure hope to see more great videos soon Louis. Hope you are well.
Nice project, great to see you back.
Thanks.
Great work and very good description . Bravo à vous monsieur !
Thank Rene, much appreciated. Regards, Louis
Very nice project. I like the touch screen with the audrino. I haven't got into using them. I have just been sticking to repairs. Might have to build some projects and utilize a touch screen interface. I liked your electronic load also. 👍
Hi Louis, very nice project and good to see you back. its obvious to see the work that has gone into the project..............thank you.................................................Berni
Hi Berni, Thought I would try something different. First project with a touchscreen. We learn as we progress :) Regards, Louis
Great work man! I respect the time and effort you put in minute details like detailed schematic drawn on white board.
I loved it all. I am also working on a similar project and would like to show you once completed. Thanks a lot, keep it up.
Thanks for your comments, much appreciated. Regards, Louis
Nice to have you back. And as usual a great video.
Thanks Christian. Regards, Louis
Most excellent presentation of a great project, especially the schematics - jawdroppingly awesome. Thanks for sharing your knowledge.
Glad you enjoyed it. Regards, Louis
glad to here you call it an electronics workshop, I don't get why so many people on youtube call it a Lab
Excellent project and presentation.
Thanks.
Nice to see yet another great project. I'll take quality over quantity with your videos every time, Louis.
Thanks Nick. I do spend a fare amount of time in preparing for my projects so it can take longer than doing reviews. I also spend time on editing my videos down to a maximum of about 45 minutes which also takes longer, especially deciding what to leave in and what to take out. Anyway just hope I get the balance right. Regards, Louis.
Awesome project. You have great projects and such good details!
Thanks. Regards, Louis
Hi Louis, Thank you once again for a great project. Bruce.
Thanks Bruce.
Welcome back! Great work!
Thanks Mauro, Nice to be back in my electronics workshop working on a new project. Regards, Louis
Interesting watch. Quick to part 2 as during the video I was curious what the overall accuracy and stability would be...
When calibrating a source, I was taught about using the first digit and decimal in lower digit numbered meters to gain a digit at the end. For example, when setting a 10 volt standard, you would adjust it to 9.9999 on a 4 1/2 digit DMM, so the digits shift between 9.9999 and 10.000, which will get you closer to a reading of a 5 1/2 digit DMM at 9.99999. This would apply to a 5 1/2 to 6 1/2 digit DMM as well, and even a 7 1/2 digit. Essentially, you're fishing for that last unseen nine and splitting hairs.
Its nice to see you're back!
Nice to be back doing electronics. Cheers, Louis
I love your videos. Learn a lot every time. Thank you!
Thanks Kostas.
Thank goodness you have this info posted I have been racking my brain for days trying to build schematic for same project. Biggest difference in mine is substituting adc to 22bit mcp3551 which may be overkill but fun to think of resolution in 6 digit ranges.
Hi Tommy, Glad to hear you found it helpful. You mentioned the MCP3551 which is an ADC, but for this project you would need to use a DAC. Regards, Louis
Scullcom Hobby Electronics my mistake, I'm trying to build more of a self calibrating type bench multimeter/power supply to clear up any confusion. It's a rabbit hole for sure. It seems that your circuit would make it easy to make an add-on board to make this work especially since you have 2 voltage references to compare against and extra unused pins. I will try to get some simulation data when I get a chance to try this. Thanks.
OK I understand now. All the best with your project. Regards, Louis
can't wait for the second part ! great video ! i learned a lot , thank you !
Thanks Anjay. Hope to start work on part 2 soon. Regards, Louis
Thank you verry much for all the effort put in your projects and videos. Learn a lot every time.
Just one idea, in terms of signal to noise ratio - isn' it better to do the higher gain in the first stage (2x 1x instead of 1x 2x) ?
Thanks this may be an option which could be done in software. I will have a look at noise in Part 2 of this project. Regards, Louis
it's great to have you again doing videos. i was very excited when i saw the notification from youtube
Thanks. Managed to get back in my electronics work shed. Regards, Louis
Great video! You did an amazing job on everything, thank you.
Glad you enjoyed. Regards, Louis
Very nice project.
Great video , well done explained . Thank you for your effort in making this project.
Thanks, Your welcome. Regards, Louis
Nice project, board looks really great. One thing to consider is the ~30 ohm Drain-Source ON resistance of the DG303, it's a little high to use in the output circuit without upset to the calibration for differing load conditions without feedback compensation. One also has to watch the switch's leakage current as well. The switches are most likely ok in in the gain stage however I didn't check the gain sensitivity for the ON resistance vs the 25K internal op-amp resistors.
Consider running the entire DAC/Op-amp chain for a fixed 10V output then use the analog switch to make a .5X ref voltage for the DAC for the low voltage range. Any switch error can be calibrated out with an adjustment resistor on the the reference and the reference .5 divider. Thanks for the video, I need to make one of these some day.
Thanks Graig for your comments. With regards the 30 ohm on resistance of the analog switch at the output. This should only be an issue once you start drawing say the higher or maximum current of this unit at about 30mA. But if the unit is used for checking the calibration of test equipment than I think it should not cause any real problems. That said, we could improve the accuracy at the higher currents by replacing the DG303B (U6) with a MAX4622 (but twice as costly) which has an ON resistance of only 3 ohm, but I would also have to alter the print layout on the PCB to match the changes in IC pin connections (maybe an option for another version of this project). Another option could be to use the existing analog output switch to control a small reed relay.
Your second point is also interesting but the current DAC (MCP4922) I am using has a maximum supply voltage is only 5.5V. Regards, Louis
As always extremely educational and expertly explained, wonderful stuff. Keep them coming.
Thanks.
Sharing your expert knowledge and encouraging the hobby engineer is wonderful. Without doubt the most educational and matter of fact electronics design engineer on here.
Thanks for your kind comment, much appreciated. Regards, Louis
Fresh content , nice video .... Thanks for that pasion you are the man
Thanks.
At the moment, I'm working hard on your DCLoad project and some modifications of mine.
And now, you push the next out - I'm on hurry, on christmas time I don't leave the lab...;-)
Nice and many thx!
Thanks Wolfgang. Looks like you are going to be busy over Christmas :-) Regards, Louis
Ohhh yeah!
Nicely drawn schematic!
Thanks.
Awesome as usual!
Thank you sir for your time and the great video.
Thanks Alexandre.
This is so awesome ❤ Thank you so much for making this educational video...
Thank you. Regards, Louis
thank you for another great educative video
Thanks Jaroslav much appreciated. Regards, Louis
Wonderful presentation.Thanks.
Thanks John.
Well done !!! Congratulations and thanks !!!
Thanks Manel.
The return of the master
Thanks :-)
Great video!
Thanks Brandon.
Really good Explanation with those Drawings! please keep your good work up;)
Thanks.
That's very very good. the whole design is great! thanks for sharing. u got it. thumbs up and subscribe.
Thanks John.
Thanks for free knowledge.
Thanks Miloš.
this gentleman is a genius
Given you can only multiply by 2 or 4, how do you get, say, 9.7V?
Great project, my friend!
As always your channel is 10.
I always follow your videos!
I already gave my like!
Michel Rio de Janeiro - Brazil
Thanks Michel, Glad you enjoy. Regards, Louis
Very very very brilliant...
Thanks Marco.
24:44 I think you did a lot of work to draw this diagramm. Great Job!
Thanks. Yes it did take me some time to draw. Regards, Louis
So you have minus 15 from the charge pump feeding a minus 15 volt regulator? so how can it regulate with no voltage to work with? you need about 3 volts across it for it to regulate
Great master again perfect job
Thanks ;-)
thanks for sharing this great project! perhaps just a tiny simplification - if the touch controller is a xpt2046, no level shifting is needed at least for the touch connections. the xpt is rated for 2.7-5v according to data sheet...
Thanks. Yes the TFT uses does use the XPT2046 touch screen controller. Thanks for the information. Regards, Louis
A dual tracking regulator might be necessary to preserve the dc accuracy of the opamps!
Excellent project
Thanks.
Surely the 7912 is a negative 12Vdc regulator not a negative 15Vdc one?
So if there are two DAC's in the package and they each have a seperate voltage ref input and each have an output, why didn't you put the 4.096 ref on one and the 1.2 volt ref on the other and just switch the output ? instead of all that switching?
wow, what would be cool is to place the 6.5 digit multimeter and the calibrator both in the same instrument enclosure 🤔 like the Ronan X86 with 2 input & 2 output leads 🤩thanks 💒
Why does your Fluke meter continue to give readings after you remove the probe from the circuit? Is this a peak hold feature? It's weird because the value keeps changing after you remove your probes.
This is due to the fact that the Fluke 8842A has an input impedance of around 10 GigOhm on voltage ranges below 20 volt. When it auto-ranges above 20 volts then the input impedance of the meter drops to about 10 MegOhm (similar to a standard multimeter) and then you don't see this effect. The residual voltage you see remaining on the display is what is held by circuit capacitance. You can zero the reading if you wish by simply shorting the test leads, if the test leads are simply left floating then the reading will take a long time to drop to zero and that the changing reading you see on the display is the effect of that. This is one of the effects of having a multimeter with a very high input impedance. But I am sure you will understand the benefits of having a very high impedance at lower voltage readings.
If you look at 40:03 of my video you will see at that point I short the meter leads together.
Regards, Louis
The MAX6(2/3)41 are actually a trade-off. The temperature coefficient isn't long term, reference drift is. the MAX63NN has roughly half the typical temperature coefficient - 0.5ppm, of the MAX62NN's - 1ppm typical. However the MAX62NN lists its long term drift spec at only 20ppm/1000 hours, beating the '63 at 30ppm/1000hours; I believe this is where their numbering scheme comes from but I could be wrong. So it's basically a trade off if you want the tightest short-term tempco, or the lowest possible long-term drift.
One very easy thing you can do is link both DAC channels with, say, a 1000:1 divider on one of them giving it the ability to "nudge" the output a little way. Between them they then act as a coarse/fine adjustment pair, greatly increasing the set resolution and possibly allowing you a digit or two more on your setting, if you calibrate it well enough
Thanks Paul for the comment. I did have in mind something similar but I am also looking at some other uses for the second DAC. I will try and cover it in Part 2 of this project. Regards, Louis
Great video! Thank you very much! I would have gone with some things different but that would be more for effect :-P
For example, I would have gone with a flyback for example for the -/+15V rails, can be implemented with something as easy to get as MC34063 maybe another more modern IC but still with trafo, it can take a wider input range, make it easy for battery conversion. Would have gone also probably for another implementation to get also negative voltages, cause why not. Could also have gone with a MOSFET reverse input protection and combine it with a soft power button. Still, the idea is pretty cool! Thanks for that!
Hi,
Thanks for your comments. It is interesting you mentioned the MC34063 as I am using that IC on a new Function Generator project I am currently working on as my next You Tube video project.
Regards,
Louis
Very nice project, you could use the 2nd dac to trim the op amp divider voltage to give smaller than mV steps.... I think you could take it down to uV levels. I did a video of my repairs to a Fluke 343A DC calibrator on my channel earlier in the year, and am in the process of a video series repairing a Fluke 5200A AC calibrator, some might find it interesting.
Thanks for your comments. I am some upgrades planned for later. Thanks for the tip on your Fluke 343A DC calibrator. Regards, Louis
Very nice video. In Part 2 it would be interesting to see what happens at the switching borders (4.000V / 4.001V and 8.000V / 8.001V ). It might turn out that 4.000V will measure more than 4.001V.
Thanks Alex for your comment. I will have a closer look at those crossover points and try and remember to show it in Part 3. Regards, Louis
Fantastic video once again. Your videos really help to make circuit design more accessible for beginners like me. I did notice that your tft refresh rate is very low. Have you considered trying the STM32F103C8T6 boards? The difference in speed is quite big, there is a comparison video between the stm32 and the arduino nano using a ILI9341 display, it really is night and day. Not to mention they can be bought for as little as $1.72 and have some other upgraded features as well.
Thanks Ronald for your comment. Thanks for bringing my attention to the STM32 board. I have not used this type of board yet but it looks very interesting and as you say the cost is very low. There must be a way of adding that type of board to the Arduino IDE software which would make life easy when programming. Regards, Louis
Hello Louis. Coming late to your nice project... I've a simple question: am I the only one to notice that the schematic around the switched OPamp doesn't fully reflect the bloc diagram? According to your long explanation about the choice of the multiplication factor 1x 2x 4x, these are cascaded by selecting x1 or x2 on both stages. But the schematic shows that the second switch actually select the output of the first OPA (x1 or x2) or the output of the fixed x2 gain of the second... Is there any advantage to do so instead of replicating the 1x, x2 gain selection of the first OPA to the second OPA?
Where do we buy the PCB?
Very nice, ty.
Thanks.
hey scullcom hobby electronics, I want to design a pH simulator which goes from( approx) -1.0000 V to +1.0000 V. I am not using a DAC or any uc. I am using 555 timer and by changing the duty cycle with two trim pots I m getting particular mv. Now the problem is I need 10 set mv values and measuring the resistance of the pot at that particular mv value this can be realized but the resistance values I m getting are not generalized values. And parallel and series combination are also not possible for the desired resistance. So can you make a video about this without using uc or DAC or at least help with this issue. Thank you.
you need to put a series resistor on the ouput to limit the current in case of a s/cregards john
Thanks John for your comment. I believe the INA105 OP Amp I use already has Output Short Circuit protection built-in, like many OP Amps these days. According to the datasheet it states that the "Output Short Circuit to Common is Continuous". Regards, Louis
Welcome back with another outstanding presentation and explanation Louis. What is the bottleneck with display refresh? the SPI bus or the AT Mega 328? Perhaps one of the STM 32 F1 "Blue Pill" kind of sort of Arduino compatible boards might be faster. Dirt cheap on Ebay
Hi Rob, Thanks, The problem is the screen refresh rate for the TFT. I am currently using the Adafruit library which may not be the fastest. I believe someone may have modified this library for a faster screen refresh rate, so I will have a look for it. I have tried in the software to only write to the TFT if something changes, this helps. Hopefully this is something that we can improve as the project progresses.
Regards,
Louis
In the design spec you said you want 1mV step. But (if I understand correctly) in the 8-10V range, your resolution will reduced to 4mV because of the x4 gain form INA105. For example if I set the output to be 9.001V, arduino will tell the DAC to output 9.001/4 = 2.25025V will is not possible for a 12bit DAC. If I really want 1mV resolution, should I use 16/24bit DAC instead?
The resolution of the 12 Bit DAC can only go down to 1mV in the current design and so in the example you gave of 9.001V which is then divided by 4, the output from the DAC will be only good to 3 decimal places so it will output 2.250V, the INA105's will then multiply that by a gain of 4 giving an output of 9.000V. If you want more resolution from the DAC then a 16 Bit DAC would be a good option but the cost of a suitable 16 DAC would increase 5 times or more. A 16 Bit DAC would increase the resolution to a few uV.
I will be looking at some update options in part 2 of this project to increase the resolution/accuracy. Regards, Louis
Thanks for sharing 😀👍
Your welcome.
always happy to have you back with amazing projects !!
sorry about the stupid question , but how can an arduino nano handle over 5volts?
Thanks. The Arduino does not handle over 5V it only operates from 5V or 3.3V supply. We use the software code programmed in the Arduino to do the calculations and output a digital representation of that information on the SPI bus to feed both the TFT display and the 12 Bit DAC. It is the DAC that generates the actual voltage output in our case up to 4.096V and it is the other two OP Amps (their gain controlled by the Arduino and the CMOS anaolg switch IC) which use a higher supply voltage of ±15V to generate an output voltage up to 10V. Regards, Louis