Author Topic: A random thread for small computing things that don't really warrant a thread of their own  (Read 190225 times)

frankly frankie

  • I kid you not
    • Fuchsiaphile
Question time - If I have a 6v battery and want to light up an LED, assuming summat like 2v forward voltage  for the LED, and 20mA, I make that a 200 ohm resistor needed, or thereabouts, or have I misunderstood how that should work?
Yep, that's right.  6V-2V gives 4V across the resistor.  4V/20mA = 200R

I would just put 3 LEDs in series, and if that's too much light, cover 2 of them with black tape.  ;)

( I used to build bike rear lights using 4 red LEDs in series and a 9V PP3 battery.  The first prototypes pre-dated the first Vistalites and were much brighter.  The design was often criticised for lacking any kind of ballast resistor but it was reliable and easily long-running enough for 4 nights of a PBP.  I later built white versions for the front but these were soon superseded by commercial designs. )
when you're dead you're done, so let the good times roll

Question time - If I have a 6v battery and want to light up an LED, assuming summat like 2v forward voltage  for the LED, and 20mA, I make that a 200 ohm resistor needed, or thereabouts, or have I misunderstood how that should work?
Yep, that's right.  6V-2V gives 4V across the resistor.  4V/20mA = 200R

I would just put 3 LEDs in series, and if that's too much light, cover 2 of them with black tape.  ;)

( I used to build bike rear lights using 4 red LEDs in series and a 9V PP3 battery.  The first prototypes pre-dated the first Vistalites and were much brighter.  The design was often criticised for lacking any kind of ballast resistor but it was reliable and easily long-running enough for 4 nights of a PBP.  I later built white versions for the front but these were soon superseded by commercial designs. )
I used that principle for some diy internal lights on a boat.

It was a bad idea.

LEDs vary in quality a lot. If you get some crappy ones, they fail closed circuit. So one fails - you now have an over voltage on the remaining ones - one of those fails - there is now a cascade that is accompanied by pretty lights, flashing and crackling noises.

Use a resistor to get the voltage correct and put the LEDs in parallel.
<i>Marmite slave</i>

The greater the ratio between resistor and LED the more consistent the current will be for different battery voltages.

With no resistor you’ll get more current on a fresh battery but probably not much more light (and perhaps, more dark) and then at the end of the battery’s life the current will drop very low and appear to last forever.

But you’d make it last even longer swapping an LED for a resistor to keep the current low throughout the lifecycle.

Use a resistor to get the voltage correct and put the LEDs in parallel.
It's usually not considered a good idea to put LEDs in parallel. The LED voltage can vary and then the current can be very unevenly distributed between LEDs in parallel.
Quote from: Kim
Paging Diver300.  Diver300 to the GSM Trimphone, please...

Kim

  • Timelord
LEDs in series with an appropriate current regulator is the 'proper' way to do it.  Which isn't to say that simpler methods aren't fine when your priority is something other than longevity.

Tim Hall

  • Victoria is my queen
Today I had to edit a document created by someone else. It's a simple table that gets printed of and stuff scribbled, by pen, into the various boxes.

It was, of course, created in Excel. Line height was adjusted by merging and centring calls.

Earlier this week someone was trying to send me a large document. I didn't need to see all the pages and the sender decided it was too big to email. He solved the problem by printing out pages, laying them on his desk, photographing them then emailing them, embedded in, rather than attached to, his emails.  xkcd 763 in real life

I need a lie down.

There are two ways you can get exercise out of a bicycle: you can
"overhaul" it, or you can ride it.  (Jerome K Jerome)

ian

  • camera nazi
I was pretty much awesomed yesterday to be in receipt of a pages of similar scanned Chinese literature (the Chinese government love sending text as pictures). That obviously wasn't the awesome part, that was the fact that my computer took the image and with no effort on my part digested all the text and and translated it into English and now I have it in a nice Word file. It's a pretty good translation too.
Authoritarian Thought Leader, the Pol Pot of Powerpoint, the Stalin of Spreadsheets

Seen on one of those electronic message boards next to the motorway:

IS YOUR CAR READY FOR WINTER NULL

Kim

  • Timelord
Seen on one of those electronic message boards next to the motorway:

IS YOUR CAR READY FOR WINTER NULL

Personalised message for Dave Null, who's in charge of hiring.  He gets so busy with all those recruitment cold-calls that people transfer to him that he doesn't always remember to service his car.

woollypigs

  • Mr Peli
    • woollypigs
MiL's ISP have done an oops.

Back in June updated the account from copper to fibre, to do that they had to create a new account and move stuff from old account over.

Though today we needed to access the old pop email but server said NO.

We had set up, waaaaaay back in time, a forward from the pop to Gmail. But over the last few years or so its become slower and slower and in the last few days it was at least 30min to get forwarded over.

I tried the webmail and the error it gave me was clearly not, a "you used the wrong password" error.

While on the phone with the ISP they said that there was never a forward setup on the old account and they had forgot to move over the email account when we upgraded back in June.

So why did it work just fine this weekend but dead today ?!?

Oh and note for all of you, as I'm sure many of you are the family IT contact. When you set up something for them, add yourself as a named contact, so you can call up and get information needed. Instead of having them call up do to get information they don't know anything about.

Even if you have access to their account portal you might still need to talk via phone with them

Today the way I managed to get the information needed. I added my email address to the account details and asked the ISP to send the info to the alternative account. So that I could log into the old POP and get the email needed.
Current mood: AARRRGGGGHHHHH !!! #bollockstobrexit

SoreTween

  • Most of me survived the Pennine Bridleway.
Backlight on my 13 year old Acer 6592G laptop just went phut.  I am upset.  It's a lovely little laptop with a gorgeous 16:10 screen, by the time it was up for renewal in 2011 (my company, my rulez) you couldn't buy anything but 16fekkin9 screens so it soldiered on in the hope that maybe next year one of the manufacturers would wise up. They didn't so it soldiered on some more.  And on and on and on not getting replaced year after year until the company was shut down just this summer.  I give thanks to the little beast for holding out until, at long last, the fad for 16fekkin9 seems to be dying.
2020 targets: None
There is only one infinite resource in this universe; human stupidity.

Kim

  • Timelord
at long last, the fad for 16fekkin9 seems to be dying.

And there was much rejoicing.   :thumbsup:

16:9 can work, if it's a massive desktop display doing the work of two conventionally-shaped monitors, but at portable sizes it's piss-poor for anything other than watching videos.  It's like they've never actually used a computer.

SoreTween

  • Most of me survived the Pennine Bridleway.
And there was much rejoicing.   :thumbsup:

16:9 can work, if it's a massive desktop display doing the work of two conventionally-shaped monitors, but at portable sizes it's piss-poor for anything other than watching videos.  It's like they've never actually used a computer.
Indeed there is and indeed it would.  A double FHD width 16:9 (3840x2160) would be a thing of extreme beauty. Also:

It aten't ded :-D 
It's just time to dismantle & reseat the screen connector again.  Usually when that starts to come loose the screen just freezes, first time the back light has flickered & gone out.

Which means my finger will have to hover over the button on the Lenovo site a wee bit longer. There was a no operating system version of that linked machine a few days ago at £100 less, if that had been in stock this morning...
2020 targets: None
There is only one infinite resource in this universe; human stupidity.

Mr Larrington

  • A bit ov a lyv wyr by slof standirds
  • Custard Wallah
    • Mr Larrington's Automatic Diary
FATBOY, the NAS with most of the important Stuffs on it, has slowed to a crawl.  If a reboot doesn't make it liven its ideas up Harsh Words will be said >:(

Edit: Seems rather more sprightly now :thumbsup:
External Transparent Wall Inspection Operative & Mayor of Mortagne-au-Perche
Satisfying the Bloodlust of the Masses in Peacetime

Mr Larrington

  • A bit ov a lyv wyr by slof standirds
  • Custard Wallah
    • Mr Larrington's Automatic Diary
Hurrah: RJ12 extension cable has touched down on the doormat :thumbsup:
Bah: MOAR sub-desk excursions required :'(

This'd better work…
External Transparent Wall Inspection Operative & Mayor of Mortagne-au-Perche
Satisfying the Bloodlust of the Masses in Peacetime

Kim

  • Timelord
Barakta just startled me by waking the Laserjet from its slumber.

Mr Larrington

  • A bit ov a lyv wyr by slof standirds
  • Custard Wallah
    • Mr Larrington's Automatic Diary
It didn’t work, because the original cable and the 'ole wot it fits into has the springy-tab-cum-grappling-hook wossname on the left while the new one has it in the middle.  What kind of gibbering halfwit thought that was a good idea >:(
External Transparent Wall Inspection Operative & Mayor of Mortagne-au-Perche
Satisfying the Bloodlust of the Masses in Peacetime

Feanor

  • It's mostly downhill from here.
Snap the offending thing off, and rely on friction / lack-of-anything-pulling-it-out?

I've seen plenty of network RJ45 cables with their wossnames snapped off still in use.

Mr Larrington

  • A bit ov a lyv wyr by slof standirds
  • Custard Wallah
    • Mr Larrington's Automatic Diary
I'm sure a good coating of gaffer tape would do the trick around the socket end, and the plug end didn’t orter move so I may yet give it a go once I've grown accustomed to the idea of deliberately breaking my new Shiny…

You can get offset cables with a plug at both ends as spares for Carrera slot-car controllers(!) but ones with the plug/socket combination have thus far eluded my Google-Fu.
External Transparent Wall Inspection Operative & Mayor of Mortagne-au-Perche
Satisfying the Bloodlust of the Masses in Peacetime

Kim

  • Timelord
It didn’t work, because the original cable and the 'ole wot it fits into has the springy-tab-cum-grappling-hook wossname on the left while the new one has it in the middle.  What kind of gibbering halfwit thought that was a good idea >:(

I don't know who they were, but I bet they were also responsible for the reverse-polarity TNC connector.

Snap the offending thing off, and rely on friction / lack-of-anything-pulling-it-out?

I've seen plenty of network RJ45 cables with their wossnames snapped off still in use.

By Chesterton's Fence I would start by assuming the tab in the different place means it might be wired differently.

Beardy

  • What’s this do?
  • I’ve always wondered where this was
Re: A random thread for small computing things that don't really warrant
« Reply #1896 on: 04 December, 2021, 09:46:52 pm »
I’ve seen RJxx cables with asymmetrical clipped plugs that are used for power. It seems like a bad idea but it does stop you putting the cables in the wrong sockets.
Sorting my life out, one shed at a time.

Mr Larrington

  • A bit ov a lyv wyr by slof standirds
  • Custard Wallah
    • Mr Larrington's Automatic Diary
Snap the offending thing off, and rely on friction / lack-of-anything-pulling-it-out?

I've seen plenty of network RJ45 cables with their wossnames snapped off still in use.

By Chesterton's Fence I would start by assuming the tab in the different place means it might be wired differently.

It's probably a reasonable assumption that the extension lead doesn’t do any fancy crossing over of conductors thobut, otherwise the vendor would have mentioned it.  Wouldn’t they…
External Transparent Wall Inspection Operative & Mayor of Mortagne-au-Perche
Satisfying the Bloodlust of the Masses in Peacetime

Kim

  • Timelord
Re: A random thread for small computing things that don't really warrant
« Reply #1898 on: 04 December, 2021, 11:06:14 pm »
I’ve seen RJxx cables with asymmetrical clipped plugs that are used for power. It seems like a bad idea but it does stop you putting the cables in the wrong sockets.

Mutant RJ-connectors seem to be de rigueur for umbilicals on barcode scanners and other EPOS/industrial things of that nature.

Kim

  • Timelord
It's probably a reasonable assumption that the extension lead doesn’t do any fancy crossing over of conductors thobut, otherwise the vendor would have mentioned it.  Wouldn’t they…

*passes the multimeter*