DE/EU Simple LM399 Reference Board, improved second Version - Page 1
Forum section: electronics / general

author: RoadRunner
author_rank: Frequent Contributor
timestamp: November 16, 2018, 09:35:29 pm
content: A little while ago i made a quick LM399 based reference board and posted on the forum. Many people have made few suggestion.So here the improved board.Now it has reverse polarity protection using P-MOSFET with Power status LEDGood quality 1K Pot in series with 10PPM 20K register for output voltage adjust-ability.Because LM399 initial tolerance is only 2% , feedback resistor value depend on LM399 initial calibration , it may range form 8.2K to 9.5KPCB Gerber and source file are available herehttps://github.com/circuitvalley/LM399_Voltage_referencehttps://www.circuitvalley.com/2018/11/diy-open-source-lm399-V2-voltage-reference-10v-dmm-calibrate.htmlThere a little video description show you temperature plot over 17 hours with temperature ranging from 14 to 27 degree C.

author: RoadRunner
author_rank: Frequent Contributor
timestamp: November 16, 2018, 09:37:21 pm
content: Quote from: Jon.C on October 09, 2018, 10:12:27 pmHere is one unit which was shipped to one forum member from previous batch.

author: RoadRunner
author_rank: Frequent Contributor
timestamp: November 19, 2018, 05:10:50 pm
content: 3 sold in one go , only two remaining

author: RoadRunner
author_rank: Frequent Contributor
timestamp: November 28, 2018, 02:16:03 pm
content: Does any one want, Last one before Christmas?

author: Iwanushka
author_rank: Frequent Contributor
timestamp: November 30, 2018, 12:58:12 am
content: I will take it.

author: RoadRunner
author_rank: Frequent Contributor
timestamp: November 30, 2018, 03:49:18 pm
content: Quote from: Iwanushka on November 30, 2018, 12:58:12 amSorry , All Gone for now, next batch after Chirstmas.

author: mk_
author_rank: Regular Contributor
timestamp: December 02, 2018, 10:12:43 am
content: Quote from: RoadRunner on November 30, 2018, 03:49:18 pmif Iwanushka is in a urgent need for the device then I will wait for the next batch even if the money arrived on your account during the next days.

author: branadic
author_rank: Super Contributor
timestamp: December 02, 2018, 12:19:05 pm
content: If someone is looking for a LMx99 based 10V reference, I should receive some boards of a PWM based voltage reference soon, hopefully next week.https://www.eevblog.com/forum/metrology/lm399-based-10-v-reference/msg1955149/#msg1955149-branadic-

author: Iwanushka
author_rank: Frequent Contributor
timestamp: December 04, 2018, 02:24:41 am
content: Quote from: mk_ on December 02, 2018, 10:12:43 amMate, thanks for your kind offer, but I'm not in a hurry I can wait for the next batch.

author: mk_
author_rank: Regular Contributor
timestamp: December 07, 2018, 12:24:12 pm
content: Parcel arrived well packed, testing later this weekendThanks a lotMichael

author: RoadRunner
author_rank: Frequent Contributor
timestamp: January 13, 2019, 02:50:07 pm
content: Board is back in stock if someone needs one please drop a pm.Thanks

author: toastedcrumpets
author_rank: Regular Contributor
timestamp: January 13, 2019, 05:52:09 pm
content: Pm sent, I'd like one please

author: RoadRunner
author_rank: Frequent Contributor
timestamp: January 14, 2019, 08:39:36 am
content: Quote from: toastedcrumpets on January 13, 2019, 05:52:09 pmyou got one, Few still available.

author: hellzakk
author_rank: Contributor
timestamp: January 14, 2019, 09:22:20 am
content: I'll take one

author: RoadRunner
author_rank: Frequent Contributor
timestamp: January 14, 2019, 11:25:10 am
content: Quote from: hellzakk on January 14, 2019, 09:22:20 amyou got one

author: nfmax
author_rank: Super Contributor
timestamp: January 24, 2019, 03:07:41 pm
content: Mine arrived safely this morning and is currently being tested. I'm using an HP 34401A which was last calibrated by Keysight on 8th January, and has a history of very good accuracy on the 10V range. At last calibration, it read 10.00002 V from a 10.0 V source (with an uncertainty of 0.000076 V). Allowing a couple of hours for the meter to warm up, then turning on the reference, gives me readings of around 10.00003V after 2 hours. It's varying a bit, but that is probably with room temperature. I'm logging that, and I will analyse the results later. The specification accuracy for the meter (10V range, 90 day) is 0.00025 V, so it is doing much better than it needs to!

author: RoadRunner
author_rank: Frequent Contributor
timestamp: January 24, 2019, 03:45:36 pm
content: Quote from: nfmax on January 24, 2019, 03:07:41 pmI am sure and happy that it matches the specs, Glad that you liked,More boards available if anyone in need.Few boards also available now with LM399H for and 42 EUR shipped within DE 45 EUR shipped worldwide. While LM399AH version priced at 50EUR DE and 53 EUR shipped worldwide.

author: DC1MC
author_rank: Super Contributor
timestamp: January 24, 2019, 07:46:24 pm
content: Is it possible to to get one as close as possible to 10V ?Cheers,DC1MC

author: RoadRunner
author_rank: Frequent Contributor
timestamp: January 25, 2019, 01:31:13 pm
content: Quote from: DC1MC on January 24, 2019, 07:46:24 pmIf i undstand correctly. You are asking about if output voltage is tunable? This is second version of the board. Previously there was no pot to for adjustment, now there a 1K pot to make fine adjusment to the low tempco gain resistors. it is possible now tune voltage to 10.00000V.Regards

author: toastedcrumpets
author_rank: Regular Contributor
timestamp: January 25, 2019, 01:46:19 pm
content: OK, I just received my purchase, the shipping was fast, you can see it took 11 days from saying I want one to it arriving!I ordered the 50 euro board. I wanted a separate voltage reference to compare my recently repaired Fluke 3330B and my Keysight 34461A against.However, between ordering this board and it arriving I actually upgraded from a 34461A to a DMM7510This means i can do some serious testing of this reference.I warmed up the DMM7510 for 90 mins and performed an ACAL. I then plugged the board into my bench PSU, first removing it from its anti-static bag, but returning it to its foam padding to reduce air currents and started logging! 5 NPLC and moving average of 20 points as recommended by the meter for maximum precision.On startup there's a rapid transient followed by a slow drift upwards over time, but the voltage is accurate to 10ppm, which is quite impressive given its just been posted, ripped open and popped on.Roadrunner, can you comment if you age these references at all? I'm going to leave it connected to my meter for a day or two and see what the performance is like over a longer time and will post again!

author: RoadRunner
author_rank: Frequent Contributor
timestamp: January 25, 2019, 02:21:19 pm
content: Quote from: toastedcrumpets on January 25, 2019, 01:46:19 pmAll Boards were aged only around 4-5 days right before i calibrate and calibration is done right 1-2 days before i ship actually handover package to post.I let board sit in free air, no any airflow arround but also with no extra insulation or anything like that.

author: toastedcrumpets
author_rank: Regular Contributor
timestamp: January 25, 2019, 03:13:30 pm
content: Quote from: RoadRunner on January 25, 2019, 02:21:19 pmI believe insulation is a good idea as in free air any small oscillations in the air flow can carry over to the package surface temperature, then into the package itself. This causes oscillations in the power to the heater which then causes oscillations elsewhere (i.e. heating lines or resistors). With insulation, these oscillations are damped, and then you only have to deal with the slowly varying lab temperature changes, which hopefully are negated by your low tempco resistors.

author: toastedcrumpets
author_rank: Regular Contributor
timestamp: January 29, 2019, 08:19:56 am
content: Just an update. The board has been on since it arrived and seemed to settle just below 10V at 9.99997.I logged the voltage over night during a lab temperature change from 21 to 18C, with a humidity close to 25%.You can see the drop in temperature quite clearly as a drop in voltage. I'm guessing it settled below 10V as you have a warmer lab than I do IIRC.I'm quite happy with this performance and will now look to make a small insulated case for it to better reduce the dependence on lab temperature, then I'll trim the pot just a little to see if I can get it closer to my 10V.One happy customer, thanks again!

author: RoadRunner
author_rank: Frequent Contributor
timestamp: January 30, 2019, 09:40:15 am
content: Quote from: toastedcrumpets on January 29, 2019, 08:19:56 amDanke

author: nfmax
author_rank: Super Contributor
timestamp: February 03, 2019, 09:41:57 am
content: Quote from: nfmax on January 24, 2019, 03:07:41 pmFinally got around to crunching the numbers & plotting the results! One vertical division on the volts axis is one LSD of the 34401A meter display. The meter had been on since about 11:00. At 12:15 or so I went into the lab and turned up the thermostat. I started logging both voltage and temperature at that time, but didn't turn the reference on until about 12:35. The thermostat timer turns the heating off at 18:00. Although the board was just sat on the bench, without a case or cover, it doesn't seem much affected by the room temperature.There are a few spikes (e.g. around 17:50 & at 20:29) where I was at the bench. Some of them directly relate to turning other equipment and lights on & off. I made an initial zero test, with power off, and during this I observed that the board - specifically the input protection MOSFET - seems to be light sensitive. A bright desk light just above it gave a few microvolts output from the reference. Presumably the DS diode in the MOSFET was acting as a photodiode, and although the epoxy package is black, it's very thin. It is possible the offset voltage of the output amplifier may also be slightly photosenstive. Voltnuts may want to remove the LED before putting it in a screened, light-tight box!

author: Mr. Scram
author_rank: Super Contributor
timestamp: February 03, 2019, 03:51:03 pm
content: Quote from: nfmax on February 03, 2019, 09:41:57 amI love that even a fairly "mundane" multimeter like the 34401A can show the presence of people in a room by measuring the small deviations they bring about in other electronics. The diode finding is also very interesting!

author: RoadRunner
author_rank: Frequent Contributor
timestamp: February 04, 2019, 09:23:21 am
content: Quote from: nfmax on February 03, 2019, 09:41:57 amThe diode finding is interesting to me as well, i will myself look into this. will share if i can come up with some results.

author: DC1MC
author_rank: Super Contributor
timestamp: February 04, 2019, 11:42:33 am
content: Quote from: RoadRunner on February 04, 2019, 09:23:21 amNo so long ago there was RPi2 that was actually fully rebooting because of a "transparent" package of the power regulator:https://www.alphr.com/raspberry-pi-2/1000375/why-a-camera-flash-will-reboot-your-raspberry-pi-2It seem that the quality of the IC packaging went down together with the priceCheers,DC1MC

author: cowasaki
author_rank: Frequent Contributor
timestamp: February 17, 2019, 03:58:26 pm
content: I would like one of these too. What is the size of the board. I’ll read the thread fully later, I take it the power requirements are in the thread.

author: RoadRunner
author_rank: Frequent Contributor
timestamp: February 17, 2019, 05:25:42 pm
content: Quote from: cowasaki on February 17, 2019, 03:58:26 pmYou got one, size is 48x100mm.

author: not1xor1
author_rank: Frequent Contributor
timestamp: February 18, 2019, 07:38:20 am
content: Quote from: RoadRunner on February 17, 2019, 05:25:42 pmSo you selected the wrong country in your account profile... obviously you are from FlatlandApart of jokes do you plan to go on selling these boards for some more time?I would like to buy one in 3-4 months (I have to move stuff around because of home renovation, HEPA filtered ventilation system).

author: toastedcrumpets
author_rank: Regular Contributor
timestamp: February 18, 2019, 09:30:13 am
content: Power requirements are low, it takes 0.15A at 15V initially while the heater is getting everything up to temperature, then it settles below 0.025A for me. You may get different results depending on air temperature and the level of insulation you have.

author: RoadRunner
author_rank: Frequent Contributor
timestamp: February 18, 2019, 10:25:48 am
content: Quote from: not1xor1 on February 18, 2019, 07:38:20 amI do have only limited time in hand to do extra stuff , so as long as something else more important does not come up it shoud be available, 3-4 Months is long time to say something.

author: jpb
author_rank: Super Contributor
timestamp: March 01, 2019, 09:21:57 pm
content: It arrived today - thank you RoadRunner.I've not insulated it but I've fed it through an LT3042 board I got from ebay to give it a low noise 15V supply.My 2015 is dead on and my 2000 is reading between 2 and 3 in the last digit.I'm very pleased though I'm not sure I like the power sockets which seem to require a fat probe to be stuck in rather than the thin wires I was trying to use - perhaps I'm using them wrong.Sorry for the out-of-focus shot of the board.Edit : the 2000 now seems steady at 2 and occasionally down to 1 in the last digit.

author: cowasaki
author_rank: Frequent Contributor
timestamp: March 01, 2019, 10:23:23 pm
content: Hoping mine arrives tomorrow. I have spare 20v AC transformers and a batch of triple DC output PCBs I designed for another project. Basically the transformer output is rectified then an electrolytic cap for positive and another for negative rails, space for a small cap per output, switching and output. The two main rails are to 7812/7912 regs then a 7805 giving the three outputs. If I build one with a 7815 and forget the neg rail it should give a perfectly stable 15v DC. How good does the supply voltage have to be? Is this up to it? If so I have some nice cases so will build it up tomorrow.

author: jpb
author_rank: Super Contributor
timestamp: March 01, 2019, 10:53:18 pm
content: I don't know how good the supply should be.I just used a (modified) LT3042 board because they are cheap on ebay (I went for a UK supplier which was £12 because I was in a hurry but the ones direct from China are less than £6). I desoldered the 33K surface mount resistor and used a Vishay 150k also off ebay. Probably way over the top but as the thing is a reference I thought it was worth over engineering.I intend to use a supply like you suggest but make it 18V instead of 15V and use it to feed the LT3042 board.

author: jpb
author_rank: Super Contributor
timestamp: March 01, 2019, 11:20:48 pm
content: As a postscript to my earlier post, I now find my meter probe is stuck in the connector! I managed to pull out three of them but not the fourth.So be careful not to use probes as connectors - just straight thick wire I guess.I must say I do not like these push connectors, I will probably have to desolder at least one to retrieve my probe. Going on the Wago web site I see that there is a special tool needed to remove wires.RoadRunner - was there a particular reason for selecting these connectors?EDIT : after pushing down hard on the white button and pulling hard on the probe it has now come out (though I did bend it in the process) So problem solved.I intend putting the board in a box with terminals so might connect these with thick copper wire (I hope this doesn't lead to emf issues arising from different metals).

author: cowasaki
author_rank: Frequent Contributor
timestamp: March 01, 2019, 11:21:43 pm
content: Quote from: jpb on March 01, 2019, 10:53:18 pmI designed the board and only actually wanted 1 with a spare but when I went to put the order in it was 80p more for 10 so I went with that and they sent 11 anyway. Somewhere I have about 7 or 8 taped together with a piece of masking tape. If I find them soon enough you can have one for the postage. The BOM is 4 x diodes, 1 x regulator, 1 x electrolytic cap (maybe 1000-2200) and I have a 100nF plus an LED and to 4 way headers. If I find the boards soon enough I'll chuck all the bits in other than the electrolytic and regulator for you but obviously you will need a transformer giving maybe 3v more than your reg.EDIT: Just added the schematic below and image of the board. With the USB isolation section empty this is the PSU I'll be using with the negative rail gone, a 7815 instead of the 7812 and no 7805

author: jpb
author_rank: Super Contributor
timestamp: March 01, 2019, 11:36:20 pm
content: Quote from: cowasaki on March 01, 2019, 11:21:43 pmThank you for the very kind offer, but I'm probably OK as I have an external (unregulated linear) supply which is basically a transformer plus diodes and electrolytic capacitor I was planning to use and then I'll just mount my 18V regulator in the box (that is my current plan - use the box as a heat sink).

author: cowasaki
author_rank: Frequent Contributor
timestamp: March 05, 2019, 06:59:43 pm
content: My board arrived this morning.I'm about 1/3 of a mV out at 10v on the Keithley 2100 about the same the other way on the PM2525. (I had to swap the power leads round).

author: jpb
author_rank: Super Contributor
timestamp: March 06, 2019, 06:27:05 pm
content: Quote from: cowasaki on March 05, 2019, 06:59:43 pmI haven't checked the specs on a Keithley 2100, but that difference seems quite large. Was everything warmed up for a while?The closeness of my results I think was slightly fortuitous as my study was quite warm (from equipment running in various experiments I'm doing) and I think RoadRunner calibrates at quite a warm 24C (that is from memory - perhaps I have that wrong) but I would still expect the variation to be a few 10s of microVolts not 300 or so.

author: cowasaki
author_rank: Frequent Contributor
timestamp: March 06, 2019, 08:02:02 pm
content: Quote from: jpb on March 06, 2019, 06:27:05 pmIt was on for hours. I've had it on again tonight and it's 9.99954 nowSo my only other reference is a £4 10v ebay reference so show here 2nd we get..So 2100 reads 9.99954 & 10.00590The PM2525 reads 10.002 & 10.010The UT60E reads 10.00 & 10.01The UNI-T 4102C reads 9.99 & 10.00Now we have 9.99965 when I switched it on cold it read 10.00118It is just sat on the desk connected to my bench power supply which is set to 15.00123 (using the 2100)

author: cowasaki
author_rank: Frequent Contributor
timestamp: March 06, 2019, 08:29:45 pm
content: According to my 4 wire PT100 probe on the 2100 the temperature is 27.197 or 27.1 with the infra-red thermometerThe temp of the LM399AH is 29.7 using the probe or 29.9 using the thermometer

author: RoadRunner
author_rank: Frequent Contributor
timestamp: March 07, 2019, 09:19:05 am
content: Quote from: jpb on March 06, 2019, 06:27:05 pmYes it seems to be quite large, Most of people i get feedback from had variation with there insturment around +/- 100 micro volts, Since toastedcrumpets pointed out ,now During calibration i cover board with 3 CM think foam, while ambieant temprature around 22C.Regards

author: cowasaki
author_rank: Frequent Contributor
timestamp: March 07, 2019, 09:43:57 am
content: Quote from: RoadRunner on March 07, 2019, 09:19:05 amSo what should I do with it as best practice? Cover it in foam in a sealed box? I can do that but wouldn’t the temperature be higher. Is my temp the reason for the low figure? The device showed a higher figure earlier before the heat increased.Thanks.

author: kado
author_rank: Regular Contributor
timestamp: March 07, 2019, 10:11:19 am
content: Hi,i have two boards and realised, that the 10 V output voltage varies in the 100s uV if the 15V input change in 100s mV below the 15V checkpoint.KarstenGesendet von iPhone mit Tapatalk

author: RoadRunner
author_rank: Frequent Contributor
timestamp: March 07, 2019, 10:27:59 am
content: Quote from: kado on March 07, 2019, 10:11:19 amThanks for pointing, yes power supply need to be as close as possible to 15V.Regards

author: DC1MC
author_rank: Super Contributor
timestamp: March 07, 2019, 04:24:48 pm
content: Quote from: kado on March 07, 2019, 10:11:19 amIs the reverse true as well, if the 15V increases over 15V the variation goes as well ?DC1MC

author: cowasaki
author_rank: Frequent Contributor
timestamp: March 07, 2019, 04:25:25 pm
content: Quote from: RoadRunner on March 07, 2019, 10:27:59 amWell the 10V board also makes a good thermometerAttached is the board when the temperature is 24.5C and the voltage is 15.0+- 0.05V10uV out which is much more like what I expected. I'm going to build a new 15v board and wrap the ref board and stick it in it's own box but with my reference resistors as wellEDIT: Just read that.... So is it better to be 0.1V over than a little under? OR as close as possible..... and just HOW close?ALSO.... Is it safe to wrap it up in foam? I don't want to damage it by overheating the board or anything like that.ThanksThis is now in the range of ..... which is out, the reference or the DMM? :-)

author: kado
author_rank: Regular Contributor
timestamp: March 07, 2019, 05:17:52 pm
content: Tune down slowly your 15V feeding source and you will get a exact 10.00000 reading. If thats the way to go with a calibration source i am not sure.Was myself astonished about that behaviour.KarstenGesendet von iPhone mit Tapatalk

author: RoadRunner
author_rank: Frequent Contributor
timestamp: March 07, 2019, 06:13:24 pm
content: Quote from: cowasaki on March 07, 2019, 04:25:25 pmOne volt difference in Supply voltage makes around 180uV difference in output because of reference zener diode current.

author: cowasaki
author_rank: Frequent Contributor
timestamp: March 07, 2019, 06:46:43 pm
content: Quote from: RoadRunner on March 07, 2019, 06:13:24 pmIn that case I need to build another power supply. I've got one on KiCAD at the moment which would do it based on the LT3080ET..... Maybe that's the way to go.

author: jpb
author_rank: Super Contributor
timestamp: March 08, 2019, 06:28:08 pm
content: My 15V was about 14.998V.I used a LT3402 board from E-bay and a 150kohm Vishay resistor also from ebay (Note a LT3405 board provides more current but are about twice the price):relatively expensive UK sourced which I used because I was in a hurryhttps://www.ebay.co.uk/itm/LT3042-Ultra-low-Noise-Ultra-high-20V-200mA-PSRR-RFLinear-Regulator-Power-Module/142890461926?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649much cheaper straight from Chinahttps://www.ebay.co.uk/itm/20V-200mA-Ultra-Low-Noise-LT3042-PSRR-RF-Linear-Regulator-Power-Module-K/283132638364?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649NB I had to desolder the setting resistor from the board and also connect the enable pin with the wire as shown in the picture on my earlier post.https://www.ebay.co.uk/itm/Vishay-S102C-150K-0-01-Metal-Foil-Resistors/352563629910?ssPageName=STRK%3AMEBIDX%3AIT&var=621889264013&_trksid=p2060353.m1438.l2649

author: kado
author_rank: Regular Contributor
timestamp: March 08, 2019, 06:44:50 pm
content: jbpthanks for the detailed information and links!Bye the way: where could one buy those fine dual banana cables? Never find them until now.KarstenGesendet von iPhone mit Tapatalk

author: jpb
author_rank: Super Contributor
timestamp: March 08, 2019, 09:04:23 pm
content: Quote from: kado on March 08, 2019, 06:44:50 pmThey are pomona ones - they are quite expensive new but I buy them if I see them going cheap on ebay - most of the time ebay is more expensive than digikey so beware!:They come in different lengths e.g.https://www.digikey.co.uk/product-detail/en/pomona-electronics/2BA-24/501-1696-ND/736429

author: cowasaki
author_rank: Frequent Contributor
timestamp: March 16, 2019, 08:26:28 pm
content: Quote from: jpb on March 01, 2019, 09:21:57 pmDo you have the schematic or other information regarding the ebay board?

author: jpb
author_rank: Super Contributor
timestamp: March 16, 2019, 08:52:45 pm
content: Quote from: cowasaki on March 16, 2019, 08:26:28 pmI don't but it there is a lot of information on the LT3042 datasheet:https://www.analog.com/media/en/technical-documentation/data-sheets/3042fb.pdfI think the board is pretty close to the schematic on the datasheet first page.I just blundered around unsoldering resistors (and accidentally unsoldering and resoldering a capacitor!) until the output was determined by the external resistor I had soldered. The board is clearly labelled underneath as shown in the attached photo. I think it was R6 I had to unsolder. You can also follow the traces from the chip if your eyesight is up to it (mine is getting a little dodgy now-a-days!)You also need to connect the enable to positive VIN (check on the datasheet).It would be neater to just connect enable to VIN on the underside of the board.I left the resistor legs very long for two reasons - one I thought I might want to use it for something else if it didn't work well on the board and secondly to avoid over-heating it when soldering (I also used a copper crocodile clip as a heat sink).Of course, you can also fit a switch between VIN and Enable if you want to turn the thing on and off.

author: jpb
author_rank: Super Contributor
timestamp: April 07, 2019, 02:45:38 pm
content: I finally got around to putting this in a case:https://www.eevblog.com/forum/metrology/encasing-of-roadrunner-lm399-10v-reference/

author: grizewald
author_rank: Frequent Contributor
timestamp: April 08, 2019, 02:50:26 pm
content: I've cased mine as well, but as I always power the reference with a bench supply, I didn't need to add any other components, just a plug for the supply and a pair of 4mm plugs for the output.The dimensions of the board are a little unfortunate as it doesn't fit inside any of the standard Hammond cases which are also tall enough. So, all I did was make a little foam igloo to keep the LM399 and it's leads warm and cosy and 3D print a couple of plastic rails to adapt the board to the case.

author: alex-sh
author_rank: Regular Contributor
timestamp: April 23, 2019, 10:49:29 am
content: Quote from: grizewald on April 08, 2019, 02:50:26 pmWell, I am not so sure about unfortunate dimension. Did you measure it correctly?This is the same LM399 board cased into Hammond 1455C1201. It is a tight fit though - I do not think you can squeeze in anything else.

author: grizewald
author_rank: Frequent Contributor
timestamp: April 23, 2019, 04:06:42 pm
content: Quote from: alex-sh on April 23, 2019, 10:49:29 amWith the insulation I added around the LM399 and allowing for the board to be held in the lowest slots on the inside of the case, the remaining 18.5mm in height was not enough. This is why I included the phrase "which are also tall enough".Maybe your LM399 is mounted closer to the PCB than mine. Did you add any insulation around the reference to quickly stabilise the temperature and avoid convection effects?

author: alex-sh
author_rank: Regular Contributor
timestamp: April 24, 2019, 06:30:51 pm
content: Quote from: grizewald on April 23, 2019, 04:06:42 pmI am not sure how close my LM399 is mounted to the board compare to yours.Yes, mine is fully insulated. In fact I put in a lot of insulation material. However, the problem I had was not height. The problem I had was length. With the banana plugs I have used, it was difficult to put it all together.

author: TA2AWX
author_rank: Newbie
timestamp: May 02, 2020, 10:32:21 am
content: Hi, good project. I recently salvaged 2 LM399AH2s from a junkyard board and thinking of making this. I readily have OP07CP opamps in my parts bin, do you think they could replace LT1001 in this project?Thanks!

author: ZhuraYuk
author_rank: Regular Contributor
timestamp: August 26, 2020, 06:36:01 pm
content: Won't variable resistor make tuned voltage incorrect due high TCR and overall instability of element, like vibrations? Maybe better decision to measure it resistance and then replace with some vishay constant value resistors?

author: pizzigri
author_rank: Regular Contributor
timestamp: September 29, 2020, 12:33:02 pm
content: Roadrunner, do you still have these boards?

author: RoadRunner
author_rank: Frequent Contributor
timestamp: September 29, 2020, 05:49:59 pm
content: Quote from: pizzigri on September 29, 2020, 12:33:02 pmYes only few boards are still available , As there is worldwide shortage of LM399AH.

author: pizzigri
author_rank: Regular Contributor
timestamp: October 18, 2020, 03:00:30 pm
content: Received my board a couple of days ago, and placing it in a box with good insulation.A question: where to get GOOD female contacts for input/output?Another thing, is there a problem in using an all-plastic ox or do I need also shielding?Heres a pic of how the ref is coming along.I made a double insulation chamber, and suspended the board using vibration absorbing rubber loops used in microphones.

author: coromonadalix
author_rank: Super Contributor
timestamp: October 18, 2020, 03:39:33 pm
content: Good setup, the board suspenders are killerI dont think the lm399 is prone to emi interferences ? personally i would have used an metallic box, but if the box is not mishandled or thrown on the floor it should be ok ?gurus here may have another view(s) ?

author: cowasaki
author_rank: Frequent Contributor
timestamp: October 22, 2020, 03:57:10 pm
content: I have a metal box within a rack unit in my workshop which contains the reference. I'm have built a decent 15v power supply and a circuit which has Botha lower and higher temperature setting. The temperatures are correct with my platinum probe to the keithley and the heater kicks in as soon as the temperature dips below the minimum and turns off as the temperature goes above the maximum. BUT I have a big over shoot in temperature which I believe is probably due to the heater element I am using which is probably too large.Question 1 - What is the best range to use?Question 2 - What is a reasonable heating element?

author: vutt
author_rank: Contributor
timestamp: February 26, 2021, 08:17:07 pm
content: I'm one of your customers who bought it this month. Package however is still in transit. But bunch of Hamon Resistor Divider Network components are already waiting on my desk.Question: Do we have long term specification for this open source solution? LM399 specification is one part of it, but this particular board have also other components. Original revision was built 3 year ago? Do youRoadRunnerhave any feedback regarding long term spec drifts?Would it be as precise let's say 5 years from now after initial calibration?

author: jpb
author_rank: Super Contributor
timestamp: February 27, 2021, 11:34:35 am
content: Quote from: vutt on February 26, 2021, 08:17:07 pmI use mine to compare my two 6.5 digit meters and also my other meters.To do a proper drift analysis would probably require measurements with a 7.5 or 8.5 digit meter - my anecdotal experience is that mine has drifted much less than the variation I see during my meters warm up period or the variation with temperature when measured on different days.

author: vutt
author_rank: Contributor
timestamp: February 28, 2021, 09:41:42 am
content: Thanks for your feedbackjpb!I think it addresses my concerns regarding this reference as long term investment. I recently acquired vintage Advantest R6551 5 1/2 digit 319999 count unit with basic 0.01%-ish 1y VDC precision with manual calibration possibility. It looks like this vref would be perfect match to calibrate that.I'm also not ruling out in longer future getting 6.5 DMM. While this ref is not meant to be calibration standard for 6.5 level DMM-s it still work out as basic DMM check.

author: jpb
author_rank: Super Contributor
timestamp: February 28, 2021, 10:53:23 am
content: If you look at this thread:https://www.eevblog.com/forum/metrology/encasing-of-roadrunner-lm399-10v-reference/msg2996906/#msg2996906I show some measurements when I first got the device and some taken much more recently which will give you some idea of the drift I've seen, though, as I say there is quite a lot of variation from temperature differences and warm up time so I cannot claim any great accuracy in what I report.I'll stick my meters on to warm up today and give you a new reading (I've left the reference powered on for the last several months now - I'm trying to get it to a settled state).I should add that I've not had my meters calibrated, the most recently calibrated one is the Keithley 2000 which I bought from Top Loser which came with a calibration. The 2015 is one I bought off ebay and re-capped and is probably a few decades old but I find they both seem to agree with each other to a difference of only about 40 microVolts once they have warmed up i.e. a difference of 4 in the last place unless you extend the digits as described in this thread:https://www.eevblog.com/forum/metrology/getting-one-more-digit-from-a-6-5-digit-meter-without-using-gpib/msg1300529/#msg1300529

author: jpb
author_rank: Super Contributor
timestamp: February 28, 2021, 03:14:03 pm
content: I've now added a reading from today to the other thread linked above.I think that the reference can be considered to be within about 100 microVolts (I know this isn't very scientific and will raise the ire of proper metriologists) but that seems to be the range of my readings over a longish time and varying temperatures and humidity levels.The actual accuracy/stability might well be much better than that but I think 100 microVolts is 10^-5 so good for 4.5 digit meters and it is good to check the agreement between my two 6.5 digit meters if not their absolute accuracy.For 5.5 digit meters a more serious set of measurements alongside temperature would need to be made and I'm not dedicated enough to do so at the present time.

author: vutt
author_rank: Contributor
timestamp: March 12, 2021, 04:43:32 pm
content: My board arrived. Working as advertised.btw. is that normal that LM399H cover is slightly loose.Anyways it's working, so I'm not complaining. Decided to build little volt ref magic box with loose components I had at hand in lockdown situation. Pic attached.