Recent Posts

1

3D printing / Re: Resize a STL File For Me

« Last post by bostonman on Today at 02:53:52 am »

Sorry, I used the term 'rotation' and meant 'revolution' (located in the design drop down menu). At one point I tinkered with revolution, and, when I accomplished a groove pattern, wondered if a difference exists.

I was able to reference the X-Z plane directly.  You have a more ways of creating reference planes in the newer versions.

I assumed the groove "reference" was the vertical part of the groove pattern, however, if this is an outdated method and revised in later versions, no sense pondering on the topic.

2

Beginners / ASUS A2500D Laptop, how to access the CMOS battery??

« Last post by CaptDon on Today at 02:52:51 am »

I can't find any useful information on the internet. The unit works but I have to hit F2 to accept the default CMOS settings, F10 to save and exit and it boots fine. I'd like to replace the CMOS battery but can't locate it. I found the RAM modules under the keyboard and the hard drive is an easy swap. Thanks for any links or info!!

3

Repair / Re: What is the exact model of this transistor?

« Last post by daisizhou on Today at 02:48:27 am »

Q209 and Q208 seem to be like this, but my fault still exists.

4

General Technical Chat / Re: Cheapest way to get date/time from GPS

« Last post by fourfathom on Today at 02:47:48 am »

Recently i commented about a RTC test using a STM32 Nucleo-L476. I estimated the out of the box frequency offset as about 10 ppm.
Meanwhile i connected a ublox 6M GPS module to the board and implemented capture of its one second pulse output using timer 1 running from LSE with a 32768 cycle (channel 3). Then i implemented frequency measurement over spans of 65 seconds (linear regression of captured timings). The diagram shows the measured frequency offsets over about 4 hours in units of the RTC smooth calibration unit = 0.954 ppm. Average offset is 9.764 ppm with a standard deviation of 0.031 ppm.
So the clock noise can be as little as one second per year.

I don't know much about the STM32, but FYI I was running a SAMD controller off it's internal oscillator (no xtal) and marveling at how accurate and stable it was.

Uh, no.

I had the controller hooked up to USB, using USB serial to communicate.  Turns out that the USB is used to monitor and adjust the internal uC clock.  When I unplugged the USB connection the internal clock became pretty awful.  It was in spec, no problem there, but the amazing accuracy was no longer so amazing.

5

Projects, Designs, and Technical Stuff / Re: Suggestions for secure authentication solution?

« Last post by DrGeoff on Today at 02:26:16 am »

What's the comms protocol? It sounds like you control both ends, so I assume you also have control over the messaging protocols and formats (APDU)?
You may be able to build the security into the messaging protocol using pre-placed symmetric keys (eg AES-256) and include the selected key number in the header of the message.
The use of small 8-bit devices in endpoints allows the use of symmetric algorithms such as AES quite easily.

6

Test Equipment / Re: Tek 2465 Horizontal Sweep Issue

« Last post by bdunham7 on Today at 02:24:28 am »

I see the problem, it's upside-downish!

It looks like it's not user error.  You can try pushing the mode selector lever down once to change from AUTO LVL to AUTO, changing the timebase and working all the pushbutton switches a few times to see if anything changes.  It probably won't and it looks like there's an issue near the U700 A-Sweep hybrid or its related circuitry.  If the cursors and readouts are working, U800 and a lot of other things are working fine.  Hopefully you have another scope to use in troubleshooting?

7

Beginners / Re: defective supercap?

« Last post by CaptDon on Today at 02:20:49 am »

You got parts delivered to Antarctica from Mouser?? It's a pain in the ass to get them to Iceland! When first applying a voltage to any capacitor it will appear as a dead short if it is in an energy storage type circuit. You have to current limit the charge with a simple resistor.

8

General Technical Chat / Re: Cheapest way to get date/time from GPS

« Last post by EPAIII on Today at 02:20:49 am »

I know that today everything is about satellites and the internet, but is there some reason why you wouldn't use WWV? It has been used for over 100 years as a world time standard.

I have a digital clock sitting here in my office that synchronizes with their broadcast signal. I bought it at Walmart for around US$35. It runs with battery power and always has the correct time. I am sure there are more professional receivers that can easily provide the time in electronic/digital form.

It is my understanding that the WWV signals (they have five transmitters on different frequencies) do reach world wide. The five different frequencies ensure that the signal can be received almost anywhere. They are run by the US Naval Observatory and have an accuracy of 100 ns of UTC. The time is encoded in the signal in a simple manner. They also provide accurate frequency signals.

I don't know if they still do, but in the past they distributed tables of the error at different times and locations so an event that was recorded at different locations could have the time differential calculated to a high accuracy at some time after recording those observations. It is older technology, but it is still there. And it is free to all.

https://en.wikipedia.org/wiki/WWV_(radio_station)

https://www.nist.gov/pml/time-and-frequency-division/time-distribution/radio-station-wwv

https://nortonsafe.search.ask.com/web?q=wwv%20receivers&ssdcat=321&lang=en&source=nag&year=2015&locale=en_us&geo=us&version=22.23.10.10&plang=sym:en&buildname=retail&heartbeatid=4ae3d98c-56e4-4df2-adf1-00b1d085e47e&eapenabled=false&env=prod&vendorid=1014930&plid=866&plgid=41&skup=21389648&skum=21376863&skuf=90001202-fa&endpointid=4ae3d98c-56e4-4df2-adf1-00b1d085e47e&lic_type=2&lic_attr=17059858&psn=7jjxx287wjvq&templatecat=sbu_w_1000_5039_n360dsp_retail&schemacat=sbu_w&schemaver=1.0.0.0&olpchannel=retail&osvers=10.0&oslocale=iso:usa&oslang=iso:eng&os=windows&showuninstallsurvey=1&installstatus=updated&vendorsrc=firefox&machinelocation=us&sw=0&3in1=0&npw=0&hp=0&dsp=0&cdest=nag&annot=false&vendorConfigured=ask&o=APN12178&prt=ngc&ver=3.21.0.6&tpr=111&chn=1014930&guid=4ae3d98c-56e4-4df2-adf1-00b1d085e47e&doi=2023-11-26&browser=FireFox&prod=DS&doi=2023-11-26&installSource=nag&cmpgn=oct23&darkMode=false&sameTabLaunch=false

9

Projects, Designs, and Technical Stuff / Re: Inverted Alligator Clips?

« Last post by rdl on Today at 02:06:52 am »

Probably not exactly what you want, but they do exist.

https://modelpaintsol.com/model-paint/reverse-alligator-clips-sturdy-bamboo-sticks-painting

10

Vintage Computing / Re: Magnetic core memory?

« Last post by amyk on Today at 01:56:49 am »

I found this module. Pls pm me if you want it.

I can't read the chip clearly, but it looks like the TI logo,
and I heard TI made a pulse sensor for the detect part of the circuit.

They look like SN1400N/SN1401N/SN1402N. Datecodes of 70xx i.e. 1970. Some have TI and some have Motorola logos. There's an interesting discussion here about whether SN14xx are actually 74xx series, which seems unlikely in that example: https://marc.info/?t=129197766200004&r=2&w=2