Author Topic: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315  (Read 30064 times)

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Offline unitedatoms

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #25 on: September 21, 2015, 12:46:22 am »
I appreciate your comments ! Thank you :)

September update: Finished the debugging of layout. Fixed a lot of simple mistakes. Reached the design goal of 0.5% accuracy in 3 of 4 ranges. The lowest impedance range is too sensitive to layout because of copper traces / probes ohmic resistance. Currently reconsidering use of several parts, replacing them with higher cost parts. About 10% of schematics changed. I will publish it ASAP.

To answer the comment about mixing the 555 chip into the middle of high cost parts.

I honestly tried to find the most advanced, contemporary, easy to use up-converter and made a lot of reading about available converter chips. There is a lot of interesting, sometimes simple and sometimes sophisticated ways to generate multiples of voltage rails with integrated DC-DC converters. At the moment with all of my knowledge, there is no single chip converter which complies to my requirements.

DC-DC power supply requirements:
- The conversion must start with control inputs being unpowered
- The conversion must stop when control inputs are triggered
- After certain period, the conversion must restart no matter what control inputs do (for example software errors, poor programming, etc)
- Converter must be "stateless". There should be no latched states, requiring software resets (for example after the overloads, thermal shutdowns)
- Converter must be popular, very well known, understood to let even unexperienced users to gain usable knowledge
- There should be multiple schematics adapted by community to allow easy upgrades, contributions to schematics from community
- Converted must have zero activity (even internal generators must stay completely) shut when required
- Converter schematics must be not tied to any advanced magnetics: transformers with calibrated gaps, ferrites with more than 500 KHz requirements.
- Magnetics for converter must be easy to implement, replace, calculate. So consequently several complex to calculate or tune designs are not acceptable: inductors with high DC bias, autotransformers energy gaps and with pulse width ratios, coupled inductors designed for super high efficiency at 1 MHz, etc.
- Diodes must be a common schotky type, not a specifically rare ones
- The design must be crude, able to start and stop in a worst supply, load conditions
- Efficiency is nice to have but is not critical. Some costly parts can be avoided since users are not interested in super high efficiency.
- Efficient board space is nice to have, but not critical
- Other details: At 3-4 watt, it should feed 6 DC rails (current prototype runs at 4.85..5.15V with current 0.89..1.25A).

- Most important requirement 1: it has to output multiple voltages.
- Most important requirement 2: it must be super easy to understand for starter.
- Most important requirement 3: It must not self destruct with 0 load conditions. Who knows what users will do during the build.

At the end I finalized my choice on 555. (At least I, myself can explain every single stage and part, why it was chosen, how to debug it, how it works).

Other details about what is being changed in power supply and what lessons learned:
- The worst mistake was choosing the particular P-MOSFET. Fixed the mistake by replacing it with "logic gate level" P-MOSFET. The lesson learned is: look at actual curves in datasheets and realize that at worst gate voltages MOSFETs behave as current limiters, not as milliohm resistors. To get to milliohm range at >1A at 4V use the "logic voltage gate" MOSFET. The cost is correlated to gate voltage capability, has to pay for it, but there is good reason why it costs so.

- The PNP current limiter from Art of Electronics. It is useful only when MOSFET control is ideal - high gate to source voltage. In situation with poorly chosen MOSFET the PNP part can be removed completely with no effect on work of the circuit. I still decided to keep PNP after upgrading to ideal MOSFET. It is yet to be seen if it helps. The thought is to protect random unpredictable external supplies from overloading. The absolute limit must be 1.1..1.2A, or else the USB supplies (even ones rated for 2A) will act up. I do not want to force users to start suspecting that their USB wall-warts are at fault (even when they most likely will be at fault if device starts consuming 2A).

- Interesting limitation of 555 chip: The reset input must not exceed 555 VCC rail even few millivolts. So I had to move reset input to blue LED with guaranteed 3V level < 4.25V VCC.

- Another correction (attached schematics has to be changed): power stage with transformer (mid tap) has to be supplied from before 1N4007 diode.

- Another improvements: Add jumpers in several test points (voltage controls, for oscilloscope, multimeter probing etc), add low ohmic resistors as current test points for approximate current measurements.

- Other good find: At low power levels and relaxed efficiency requirements - copper wire of transformer coils works as a free low-ohm high power resistor. It is OK to treat it as resistor for up to 0.25W with no problems.

BTW: 1N4007 may look like another cheap offence to surrounding high cost parts. The reason to choose 1N4007 (not even lower 1N400X) is that I needed indestructible piece of very low doped silicon to have the simple isolating DC switch with leakage current at very low nA level.
« Last Edit: September 21, 2015, 01:29:04 am by unitedatoms »
Open Hardware DIY Kit LCR/ESR Impedance meter UA315
 

Offline timofonic

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #26 on: September 24, 2015, 07:20:37 am »
@free_electron

You  may be right, but you can be more constructive too. I understand some things can be an aberration for you, because you are very highly skilled. I really appreciate your works and contributions to the community, I want to buy some of your books when I get enough incomes too.

But it would be nice if you are a bit more friendly and provide better feedback, please not traumatize newbies! People do mistakes, we are here to learn, discuss and help each other :)
« Last Edit: September 24, 2015, 07:27:16 am by Circuiteromalaguito »
 

Offline Towger

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #27 on: September 24, 2015, 07:49:24 am »
@free_electron

You  may be right, but you can be more constructive too.
I agree. The op has designed and is close to release their project. But there is still no sign of your improved version of the ESR/component tester.
 

Offline unitedatoms

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #28 on: October 08, 2015, 01:16:04 am »
October 7th update:
- Analog board UA315 Version 2. Fixed multiple errors in schematics (missing levels conversion for several digital lines), upgraded output amplifier, upgraded analog switch, fine fixes for DC offsets, more filters for DC rails, star grounding, better pairing of layout for DC rails, shielding for isolation of sensitive inputs from outputs (copper ring), shielding of noisy outputs (thick copper ring), single point connects for grounds from multiple DC rails, added multiple test points with jumpers, better attention to silkscreen labels, upgraded transformer with more taps (12 pins).

- Board size reduced to 102x180mm, was 99x199mm (x99 values is to fit into stupid dropdown choice of some other PCB house).

- Ordered the 5 boards batch from Elecrow. Same company, as for first version.

- This board is expected to be final (placement, routing wise, some resistors choices may still vary). The software is 50% ready and has satisfactory accuracy, readability, speed for 3 of 4 ranges.

I will update how well the V2 build behaved later this month (in October). Couple of parts are still to be ordered from Mouser/Digikey.

The purpose of 1st board is accomplished: to evaluate the noise (bobbing) of measurements. The bobbing is very low, in some ranges the repeatable reading have 0 to 1-2 steps of least significant position (full range is about 10000..20000 counts). The residual noises, interferences are not from any power supply or CPU board, the spikes in bobbing comes only from clocking circuit. This gives me hope that precision of 4-5 digits with minimal bobbing at 4th-5th digit is achievable in final build.

Other note: the joint points count is above 800 per board, which is close to 1000 points of license limit for DipTrace. There are multiple annoyances in Diptrace, but it is too late to change the CAD. BTW, the whole analog board is 100% hand routed. It took about 10 days just to place and hand route it, I really enjoyed may be first 5 days of it :)

Lessons learned: For any future complex designs, I will choose in favor of more smaller boards, than less amount of large boards. The connectors and cables are costly, but it would make the project so much easier to work with, when obviously independent modules are separate. For example power supplies array can be easily separated from analog frontend + digital-to-analog core.
« Last Edit: October 08, 2015, 01:41:55 am by unitedatoms »
Open Hardware DIY Kit LCR/ESR Impedance meter UA315
 

Offline unitedatoms

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #29 on: October 09, 2015, 06:55:45 am »
October 8th update:
While waiting for boards from Elecrow, I am writing notes. The article about ferrite transformer: http://unitedatoms.com/articles/ferrite-transformer-design-using-pc40-tdk-pot2213-core/


And the up converter schematics related to transformer.


The finalized part number for transformer will be RM10 with 12 pin bobbin and +2 pins for clamps B65814B2203X000. So I am getting rid of POT2212 transformer cores on eBay (USA only). Those are good and tested, but are too large / too powerful and occupy way too much space on the board.

Open Hardware DIY Kit LCR/ESR Impedance meter UA315
 

Offline Vgkid

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #30 on: October 09, 2015, 06:59:14 am »
Looking forward to more progress.
If you own any North Hills Electronics gear, message me. L&N Fan
 

Offline unitedatoms

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #31 on: October 09, 2015, 02:20:27 pm »
Looking forward to more progress.

Thank you for your interest in this topic. I have added 4 articles to start explaining the design in details, while waiting for PCBs.

Project design articles, in depth:

part-1 "Only R and Time reference needed"

part-2 "Ratiometric use of AD5933"

part-3 "Complete exclusion of DC from measurement"

part-4 "ESR meter vs Network Analyzer"

part-5 "First seven prototypes"



« Last Edit: October 10, 2015, 04:26:44 am by unitedatoms »
Open Hardware DIY Kit LCR/ESR Impedance meter UA315
 

Offline Vgkid

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #32 on: October 09, 2015, 04:25:49 pm »
That is a very nice write up.
If you own any North Hills Electronics gear, message me. L&N Fan
 

Offline timofonic

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #33 on: October 11, 2015, 10:31:34 pm »
Great!

Are you considering switching to KiCad? I know it might be hard at first, but you might about these limits and make it true OSHW ;)
 

Offline kripton2035

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #34 on: October 11, 2015, 10:45:24 pm »
great explainations.
did you consider including some pictures in your articles ? would be easier to read.

Offline timofonic

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #35 on: October 12, 2015, 06:43:59 am »
@free_electron

You  may be right, but you can be more constructive too.
I agree. The op has designed and is close to release their project. But there is still no sign of your improved version of the ESR/component tester.

He would suggest improvements and be more didactic, instead doing a rude reply.

I just hope he had a bad day and apologize about it. I appreciate a lot his skills and knowledge, but not in this way.

People make mistakes, please be constructive and help others to make better designs instead demotivate them ;)

I suspect he will not reply again. I hope he surpasses his proud and meditate about his attitude. Everyone acted wrong, nobody's perfect. But we can always improve, even if you are a guru.
 

Offline PointyOintment

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #36 on: October 12, 2015, 03:27:35 pm »
I have for a while wanted a good LCR/ESR meter, but never saw one I liked for a price I liked. I was considering building one, but it would have been nowhere near as well designed as this, so I think I'll build one of these once the design is stable and tested. Do you think it would work well using a Teensy 3 as the controller?

Also, here's a very simple OSHW milliohmmeter for finding shorts, for reference/inspiration: https://hackaday.io/project/3635-shorty-short-circuit-finder

Offline unitedatoms

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #37 on: October 12, 2015, 03:44:31 pm »
Great!

Are you considering switching to KiCad? I know it might be hard at first, but you might about these limits and make it true OSHW ;)

Thank you, this is good suggestion. First, I will publish all design files in DipTrace format. I tried to use KiCad long time ago, but stuck with very odd UI/User Experience, it was very counterintuitive. As soon as the schematics will be stabilized and solid, I hope someone will redraw it in KiCad, or I will try drawing it myself. Yes, OSHW should be available in KiCad and PDF.
Open Hardware DIY Kit LCR/ESR Impedance meter UA315
 

Offline unitedatoms

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #38 on: October 12, 2015, 03:48:09 pm »
great explainations.
did you consider including some pictures in your articles ? would be easier to read.

Thank you. I will add more pictures, yes. The current pictures are mostly about how this theory of operation is different to common LCR theory. The part 5 of story is just list of my personal mistakes, I will think what pictures to add there. Most of the prototypes were cannibalized for every next prototype, so I thought the pictures of junk boards midway to final boards are not very interesting.

Edit: I keep adding pictures to the article.
« Last Edit: October 14, 2015, 01:46:24 am by unitedatoms »
Open Hardware DIY Kit LCR/ESR Impedance meter UA315
 

Offline unitedatoms

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #39 on: October 12, 2015, 03:58:33 pm »
Do you think it would work well using a Teensy 3 as the controller?

Also, here's a very simple OSHW milliohmmeter for finding shorts, for reference/inspiration: https://hackaday.io/project/3635-shorty-short-circuit-finder

I think it will work with any CPU at 3-3.3V logic levels. The analog board has 34 pin 0.1 male shrouded connector. It supplies only 5V/200-300mW for digital side.

I was expecting that there will no single digital choice acceptable by everyone. Everybody will like their own favorite CPU, USB IO extender, separate PC, Bluetooth etc.

So I stopped trying to make interface completely universal. For perfectly universal digital IO interface between measurement board and CPU in next versions or close future, I would think of optically / galvanically insulated IO with some kind of slow miltipin extenders on analog side.
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Offline unitedatoms

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #40 on: October 16, 2015, 01:56:43 am »
October 15 2015. Prototype #8 progress update:


The transformer RM10 with 12 pins is ready and has following winding details. All coils are 0.33 magnet wire.
  • Primary pins 1-2-3 is 4+4 turns (4.4V)
  • Pins 4-5 is 9 turns (7.5V)
  • pins  6-10 is 6.5 turns (5V)
  • pins 7-8-9 is 21+21 turns (+15V/-15V)
  • pins 11-12 is 33 turns (27V)

 

The DC voltages after rectifiers on supercaps unloaded with input USB voltage 5.02V at the beginning of cable, 5.00..5.01V at the screw terminal.

Results: before the LM317/LM337 regulators were soldered.

5V rail unregulated: 5.19V - little bit (56mV overshoot) more than precalculated range of +4.846..5.134V

7.5V rail before regulator 5V analog: 7.15V is 350mV less than expected range 7.269..7.701V

15V rails before regulators: +17.42, -17.40V perfectly in range of precalculated range 16.961..17.969V

26V rail: + 27.37V perfectly in precalculated range 26.653..28.237V

3V rail: no regulator is soldered yet


October 21st 2015: FedEx is delivering the Mouser's box with parts ... just about now ...
Update: The 1.3K resistor made the rails voltages look better. Also the NDP6020P Logic Level P-FET now does not require 5.25..5.5V supply, 5.000V is enough. Resulting voltages of unloaded rails:

Pulsed USB voltage +4.962V/1.36A at input of DC-DC converter
Filtered output of DC-DC converter:
-17.445V before, -15.082V after -15V regulator
+17.437V before, +14.969V after +15V regulator
+27.45V unregulated LED supply
+5.077V unregulated 5V supply
+7.103V before, +5.035V after +5V regulator, +3.039V after +3V regulator


Wrapping up the power supply part as a blog article:
http://unitedatoms.com/articles/impedance-meter-ua315-part-6/
« Last Edit: October 23, 2015, 07:20:42 am by unitedatoms »
Open Hardware DIY Kit LCR/ESR Impedance meter UA315
 

Offline timofonic

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #41 on: November 04, 2015, 11:51:15 pm »
Great!


Wow, the board with supercaps is massive!

Please provide updates in the forum, as I'm used to read it more frequently than a blog ;)

Is that transformer difficult to obtain? Why so much voltages?

How did you draw these schematics? They look simple and nice. I only see some pixelation in the cylinder, the result is simple and very clear. I wish to be able to do it at least a quarter as good as you, I'm awful at drawing.

Did you use raster images for compatibility reasons? SVG would be nicer, but I understand it.

I find amusing your use of old school parts with the supercapacitor array, it's a bizarre design. Are they expensive? I still don't understand well why you used it, it seems it's used to avoid noise.

Why did you make your own custom Arduino+GPU? What GPU did you use? I had no idea MCUs would need a GPU for this.

What's the advantage of a custom impedance meter instead a more flexible equipment?
 

Offline tridentsx

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #42 on: December 05, 2015, 07:05:45 pm »
Great!

Are you considering switching to KiCad? I know it might be hard at first, but you might about these limits and make it true OSHW ;)

Thank you, this is good suggestion. First, I will publish all design files in DipTrace format. I tried to use KiCad long time ago, but stuck with very odd UI/User Experience, it was very counterintuitive. As soon as the schematics will be stabilized and solid, I hope someone will redraw it in KiCad, or I will try drawing it myself. Yes, OSHW should be available in KiCad and PDF.

I had the exact same experience tried KiCad many years ago and quickly discarded it as a waste of time. Last month I saw some article about Cern investing in KiCad adding push and shove routing, controlled impedance, matched length tracks etc ... and I decided to try it again. This time it didn't crash all the time and I am positively surprised with the later versions of KiCad and have decided to make all my layouts in KiCad going forward.
 

Offline tridentsx

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #43 on: December 05, 2015, 07:30:01 pm »
I  don't know were your price point is for usb panel mount, this is the cheapest I have found
http://www.vpi.us/cgi-bin/vpi/pm-usbbf-usbaf.html
 

Offline timofonic

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #44 on: January 09, 2016, 04:06:32 pm »
Any news about this project? I really miss to see those frankenboards and articles :D
 

Offline Vgkid

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #45 on: March 04, 2016, 10:23:17 am »
Any updates.
If you own any North Hills Electronics gear, message me. L&N Fan
 

Offline Dave Atom

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #46 on: March 14, 2016, 11:18:47 pm »
Watching with a great interest, any news ?
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Offline kandrey89

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #47 on: July 06, 2016, 08:53:44 am »
Thanks for the project, updates and insights, looking forward to further updates.
 

Offline xaled

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #48 on: August 29, 2016, 11:11:11 pm »
I'm also interested in the project and updates.


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Offline julian1

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Re: OSHW LCR/ESR Impedance Meter. DIY benchtop kit UA315
« Reply #49 on: September 10, 2016, 11:17:41 am »
Super interesting project!

I feel it would benefit from,

  - Having the schematics/pcb layout (kicad?) and reference source-code on Github, available for anyone to fork, adapt or modify.

Other OS instruments/tools like the BusPirate succeed in large part because of the plugin software architecture, that allows people to write modules to adapt it for their own specific needs, while adding-value to the whole.

Thinking about the different functional adapations - impedance meter, LCR meter, low-frequency VNA, and I supect this will be too much work for one person to get the software and G/UI right.

  - Slightly more modular design. The power-supply design represents a very specific set of design choices. It might be good to be on a separate board.

  - SMT parts alternative. I suspect a lot of folks interested in assembling a project like this wouldn't be afraid of trying toaster-oven type reflow.

« Last Edit: September 10, 2016, 11:42:09 am by julian1 »
 


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