Test Equipment Anonymous (TEA) group therapy thread

[Brumby]

Mnem, that is just sad.

You need to set down roots, get your gear up to the GWN and dive into some meaty exploits.  This diet of corn chips cannot be tasty or satisfying....

[tonyalbus]

No a pure TEA stays 

[McBryce]

As someone who likes to wear T-Shirts I wanted to have one with a TEA logo on it.
But I wasn't able to find such a logo, perhaps I've overlooked it somehow.

If we don't have a TEA logo, is there somebody here with us with some
graphical and artist talents (and is willing to do) who could create such a logo?

My abilites in this respect are fairly mediocre.

Any ideas, how such a TEA logo should look alike?

A pile of test equipment beside a rabbit throwing dollars out the window and below the word TEA in the colours of Fleabay?

McBryce.

[mnementh]

@McBryce - So... pretty much just a pic of Tony's bench then...? 

mnem
 

[Ice-Tea]

On the topic of T-shirts:

[mnementh]

   I'm currently reverse-engineering a cheap motion-sensing LED Light Blub. Does that give you hope...?

mnem
};=)~~~~<

Mnem, that is just sad. You need to set down roots, get your gear up to the GWN and dive into some meaty exploits.  This diet of corn chips cannot be tasty or satisfying....

Ehhh... this is my first afternoon off just trying to recover from the back pain of moving; thought I'd tackle something simple and domestic. I want to use this motion sensor blub in a bathroom, but it appears these stupid things all have a dawn/dusk sensor as well, so intended for outdoor use. I'm trying to characterize the value of the CDS to select a fixed resistor to replace it with so it would work in an environment where there would still be ambient light a lot of the time.

But... of course Murphy has other plans. After trying several different resistors and a couple pots, I found I could get the bulb to either light continuously or stay off, but not to actually do the motion sense thing.

Several times I read the destructions to understand how it works; then I realized the problem: The first thing the bulb does at power on is test and cal itself by turning the LED array on and reading the CDS. With a fixed resistor, either it reads light level above threshold or below... but never detects a change to cal itself.

Doing a quick swing with a pot proved this behavior... but it means that this blub is probably not suitable for an indoor application where there will sometimes be ambient light unless I can force it to cal at just the right brightness level for both daylight and dark.

Outsmarted by a fukkin' light bulb... shoulda seen it coming. 

mnem
 

[SilverSolder]

[...]  it appears these stupid things all have a dawn/dusk sensor as well, so intended for outdoor use. I'm trying to characterize the value of the CDS to select a fixed resistor to replace it with so it would work in an environment where there would still be ambient light a lot of the time. [...]

I solved a similar problem recently by painting over the sensor with dark paint! - Crude, but worked perfectly.

[bd139]

On the topic of T-shirts:

Hahahaha I need that. Defpom

[bd139]

[...]  it appears these stupid things all have a dawn/dusk sensor as well, so intended for outdoor use. I'm trying to characterize the value of the CDS to select a fixed resistor to replace it with so it would work in an environment where there would still be ambient light a lot of the time. [...]

I solved a similar problem recently by painting over the sensor with dark paint! - Crude, but worked perfectly.

Black electrical tape. Also works on offensively bright blue standby LEDs 

[mnementh]

Yeah, black electrical tape won't work; the CDS has to operate at some level or the thing never completes its POST cal process. I was thinking of trying layers of translucent tape or somesuch to make it cal to a scale which is offset towards the bright range. I'll cogitate on it over lunch.

mnem
 

[SilverSolder]

Yeah, black electrical tape won't work; the CDS has to operate at some level or the thing never completes its POST cal process. I was thinking of trying layers of translucent tape or somesuch to make it cal to a scale which is offset towards the bright range. I'll cogitate on it over lunch.

mnem
 

Make a kind of "light tunnel" over to the LED (maybe a straw?), and tape/paint out the external environment?

[Wolfgang]

On the topic of T-shirts:

Hahahaha I need that. Defpom

... another suggestion see below:

[FransW]

Suggestion t-shirt

[med6753]

On the topic of T-shirts:

Hahahaha I need that. Defpom

... another suggestion see below:

That's coming closer to me like but not thrilled with the Marty Feldman.

[BU508A]

We can use a smurf instead ... what do you think?

 

[mnementh]

I have mine... y'all can do WTF-ever you like with yours. 

mnem

[med6753]

We can use a smurf instead ... what do you think?

 

Nah.  How about this instead in the center?

[med6753]

Or maybe this one?

[Kosmic]

I'm still working on a distribution amplifier to put in an enclosure with my rubidium standard. This is my ugly prototype, with isolated output, based around the LM7171 opamp (because I got a lot of them at hands).



In yellow the output of the function generator, In blue the output of the distribution amplifier.


Mostly working fine excepted for a small attenuation at the output due to the transformer.



The next picture show the fft of the output. As you can see, the harmonics of the rigol function generator (temporarily providing 10Mhz) are accurately reproduced



Now I need to decide if I continue the prototype and populate the 7 missing outputs, or if I improve my kicad skills and move everything to a real PCB ?

[mnementh]

 Izzat holesaw-pad construction I see...? How much PITA in real use?

mnem
*pats belly* Sooooo much pizza... *Grooooooannnnnnnnnn*

[Robert763]

Well those are not real LM741s. The 741 has a gain bandwidth of about 1.5MHz. Amplitude is also limited by the slew rate of 0.5V/us.
No way are you getting a gain of 1 out of a 741 at 10MHz.
Also have you loaded the output? should really be able to drive 50R. A old composite video amplifier works well especially if you put a ethernet isolating transfoumer / balun on the outputs. The Extro ones ae very nice. A VGA one with BNCs will also work.

DOH,
IDIOT I saw 741 not 7171 DOH.

[Kosmic]

Izzat holesaw-pad construction I see...? How much PITA in real use?

mnem
*pats belly* Sooooo much pizza... *Grooooooannnnnnnnnn*

Yes my first tentative. Got the bits from china a while ago.



In term of usage, it's pretty easy if you have a drill press. A lot simpler than cutting pad with the nibbler and then gluing.

[factory]

Today's delivery fail, a sample of Chinese number readout bulbs, the total lack of packaging resulted in bent pins and one being completely smashed. 

Well, what can you expect for 0.78 GBP?

Both the description* & declared value are wrong, they were just over £5 each.

David

*Unless they actually are a new type of fuse. 

Individually tested of course.

This is a case where you lead with a request for them to initiate a shipping insurance claim.  The assache factor will give you some small amount of leverage, and no small amount of satisfaction.

mnem
 

Well I opened a claim last night, I mentioned the damage, poor packaging* and added lots of pictures.
Got a stupid reply this morning

whats wrong with the items ? can u give us more details ? i will solve it for u

 
Sent the details again & pointed out previously added pictures, hopefully they will take notice this time as I can't escalate until the 11th.

*On the plus side they were individually bagged in glass shard containment zip-lock bags.

David

[Kosmic]

Well those are not real LM741s. The 741 has a gain bandwidth of about 1.5MHz. Amplitude is also limited by the slew rate of 0.5V/us.
No way are you getting a gain of 1 out of a 741 at 10MHz.
Also have you loaded the output? should really be able to drive 50R. A old composite video amplifier works well especially if you put a ethernet isolating transfoumer / balun on the outputs. The Extro ones ae very nice. A VGA one with BNCs will also work.

LM7171 has 200Mhz unity-gain bandwidth. In simulation I was able to get 150Mhz easy.

For the transfo I think I saw in the spec something like 2db attenuation. I need to check back.

[Cerebus]

How about something a bit more graphical (and yes, a bit Katherine Hamnet):