Author Topic: EEVblog #813 - Mailbag  (Read 16399 times)

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Offline Don Hills

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Re: EEVblog #813 - Mailbag
« Reply #25 on: November 04, 2015, 12:07:41 am »
On the subject of the Thandar scope:
The blue wire wrap winding on the transformer is almost certainly the filament power winding for the directly heated CRT tube.
 

Offline jnissen

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Re: EEVblog #813 - Mailbag
« Reply #26 on: November 04, 2015, 01:46:23 am »
(Interestingly, it has CAT I on the front, unlike the Harbour Freight meter)

I love how the Cen-Tech meter is marked as being Cat II rated  :-DD

Just depends on your definition of CAT! Meow!
 

Offline gordo51

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Re: EEVblog #813 - Mailbag
« Reply #27 on: November 04, 2015, 02:07:53 am »
I can see it will not be too long before Dave2 is laid off and Sagan takes over. Pretty clever and articulate for a 4 year old.
One problem I have had with cheap multimeters is that they do not have a Lo Batt indicator. I was tearing my hair out once checking something with a cheap meter, Radio Shack I think, and finally concluded the meter was wrong. Turned out the 9v battery was way low. No cheap meters any more, just Fluke or Tektronix.
 

Offline crispy_tofu

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Re: EEVblog #813 - Mailbag
« Reply #28 on: November 04, 2015, 02:16:10 am »
One problem I have had with cheap multimeters is that they do not have a Lo Batt indicator.
I'm pretty sure the DT830 has a battery indicator on the bottom left of the LCD, but those multimeters tend to drift a lot when the battery is low, exactly what you describe.  :-+
 

Offline Alexei.Polkhanov

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Re: EEVblog #813 - Mailbag
« Reply #29 on: November 04, 2015, 03:53:23 am »
 

Offline djQUAN

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Re: EEVblog #813 - Mailbag
« Reply #30 on: November 04, 2015, 04:12:53 am »
I have seen a glass breakage detector with an internal lithium coin battery.

The battery runs the circuitry and the two wires are simply a normally open contact (open collector).

Maybe that is the case with the cell inside the intrusion detector.
 

Offline bills

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Re: EEVblog #813 - Mailbag
« Reply #31 on: November 04, 2015, 05:49:18 am »
What ever the battery is for it is no doubt dead by now,so it's purpose is moot. 
Never argue with idiots. They drag you down to their level and beat you with experience.
 

Offline AmmoJammo

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Re: EEVblog #813 - Mailbag
« Reply #32 on: November 04, 2015, 08:30:06 am »
Is it just me or does Sagan sound a tad British?

Probably Pepper Pig & Mr Maker!

LMAO! I knew that when I heard him speak!  :-DD

Don't let him park his car on a 50 degree slope like Peppa Pig does though!
« Last Edit: November 04, 2015, 09:22:26 am by AmmoJammo »
 

Offline bookaboo

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Re: EEVblog #813 - Mailbag
« Reply #33 on: November 04, 2015, 11:23:12 am »
Is it just me or does Sagan sound a tad British?

Probably Pepper Pig & Mr Maker!

Was thinking exactly that, we have the same problem here. The word generally used (slang if you want to call it that)  for mother here was "mammy", now all the 5 year olds including mine refer in an oxbridge tone to their "mum".
 

Offline f4eru

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Re: EEVblog #813 - Mailbag
« Reply #34 on: November 04, 2015, 12:35:03 pm »
(Interestingly, it has CAT I on the front, unlike the Harbour Freight meter)

I love how the Cen-Tech meter is marked as being Cat II rated  :-DD

Just depends on your definition of CAT! Meow!

Probably it can hold the weight of two stacked cats.
 

Offline kfitch42

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Re: EEVblog #813 - Mailbag
« Reply #35 on: November 04, 2015, 03:24:58 pm »
Hearing about Kindergarten orientation, then watching Sagan play with those Makerbeam thingys made me think about what will happen the first time he gets a homework assignment along the lines of "Using common household object build a diorama of your community."

I suspect Sagan might end up leaving a wake of "reactive rules" as he progresses through school. The year after him will have lots asterisks on their assignments like "* High voltage power supplies and nixie tubes are NOT common household objects."
 

Online Towger

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Re: EEVblog #813 - Mailbag
« Reply #36 on: November 04, 2015, 03:35:51 pm »
Was thinking exactly that, we have the same problem here. The word generally used (slang if you want to call it that)  for mother here was "mammy", now all the 5 year olds including mine refer in an oxbridge tone to their "mum".

That depends on the area you are from. We never said mammy, my 5 year old says mummy and the 8 and 9 have progressed to 'Mother', in a posh accent...
 

Offline Stonent

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Re: EEVblog #813 - Mailbag
« Reply #37 on: November 04, 2015, 05:00:37 pm »
We can't have Sagan getting a British accent, we need to start him watching old episodes of Mr. Wizard and we can Americanize him.

Heathkit Hero 1 Mini Teardown:



Sounds like Hero has a Votrax SC01 accent.
« Last Edit: November 04, 2015, 05:06:25 pm by Stonent »
The larger the government, the smaller the citizen.
 

Offline SeanB

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Re: EEVblog #813 - Mailbag
« Reply #38 on: November 04, 2015, 05:33:46 pm »
Thandar/TTI/whatevertheyarenow made a whole range of test equipment in that same case, all using the same front panel switches and knobs. The scope was the one, and there was a function generator as well. All battery powered.

I still have a SC110A I got in school many years ago. It worked well for many years till it finally died. I should look to see if I can fix it some day, as I can now get the manual online for it. IIRC it was a $200 scope, my dad bought it in Hong Kong on a business trip to Japan when he went to Toyoda to see the Toyota works. Still have a paper picture of Mt Fujii on the wall, apparently they are collectors pieces now. He went on a tour there with Toyota, and this was one of the places he visited and this was a gift.
 

Offline apis

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Re: EEVblog #813 - Mailbag
« Reply #39 on: November 04, 2015, 11:46:55 pm »
I got a couple DT830 from ebay for 1$ including shipping (each), what surprised me was that there are different versions, some crappier than others. They probably use the same chip but circuitboard and the cases were different, one didn't even have a trimmer pot.

And wrt the alcohol tester, Iv'e seen a teardown of a alcohol tester that works, it had an air pump so it could sample a known volume of air and the sensor had to be calibrated regularly. That one from ebay must have had some very nice sensor in it, or maybe not. ::)
 

Offline bookaboo

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Re: EEVblog #813 - Mailbag
« Reply #40 on: November 05, 2015, 10:31:13 am »
Was thinking exactly that, we have the same problem here. The word generally used (slang if you want to call it that)  for mother here was "mammy", now all the 5 year olds including mine refer in an oxbridge tone to their "mum".

That depends on the area you are from. We never said mammy, my 5 year old says mummy and the 8 and 9 have progressed to 'Mother', in a posh accent...

Im in the north west, I always thought Mammy was standard across the board? Im thinking south Dublin the exception. Certainly never heard "mother" or "mum" until recently :)
 

Offline Robomeds

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Re: EEVblog #813 - Mailbag
« Reply #41 on: November 05, 2015, 03:36:59 pm »
There are many many different 830 meter designs.  The HF ones seem to be the cheapest (price and construction).  But even the HF meters vary quite a bit.  Just from threads around here...
https://www.eevblog.com/forum/reviews/harbor-freight-cen-tech-90899-small-teardown/msg181243/#msg181243
https://www.eevblog.com/forum/reviews/harbor-freight-cen-tech-90899-small-teardown/msg181264/#msg181264

Non HF versions
https://www.eevblog.com/forum/testgear/world's-cheapest-multimeter-teardown/

I've wounder if the meter in question was adjusted before being sent to Dave.  I've tested perhaps 6 or 7 of these things against other meters (Fluke 87-3 and 87-5, not true calibration equipment) and found none out of spec and most within a few counts.  That does speak well of the IC used in the things.  Currently I have I think 5 of them.  3 in the pile, one in each car.  The local school was throwing them out (maybe someone pointed out the near total lack of safety circuitry) so I picked them up as give aways and back of the car meters.  I see them as better than nothing if you know their safety limits.  Never my first choice. 
 

Offline bloguetronica

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Re: EEVblog #813 - Mailbag
« Reply #42 on: November 07, 2015, 06:52:12 pm »
Dave, first of all I want to thank you for the excellent review you've made on the GR10M board I've sent you.

You did point some valid aspects, some of which I can't implement due to the nature of the project and the enclosure used of it, which is an Hammond 1455D601. I guess where won't be space for holes (nor need to) or BNC connectors. I know the SMB connectors are not very durable, but the other option would be to go for SMA, which is even worse IMHO. However, the voltage rating idea printed on the silkscreen is a nice feature that I've already implemented on my next project, and all thanks to you.

I'm worried about the state of your board, since F1 seems chipped to me. I could swear the board seemed to be fine when I sent it to you. Since I never wished to sent you something that is broken (or got broken during transportation), I can send you a replacement polyfuse. Please, could you confirm if F1 is damaged? Thanks in advance.
 

Offline twice11

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Re: EEVblog #813 - Mailbag
« Reply #43 on: November 08, 2015, 01:37:06 pm »
I'm pretty sure the DT830 has a battery indicator on the bottom left of the LCD, but those multimeters tend to drift a lot when the battery is low, exactly what you describe.  :-+

Actually, the 7106-based 9V multimeters are quite good at handling low battery. The configuration is basically a zener diode for the reference voltage which is tapped by the pot together with fixed resistors to produce 100mV. Typically the LCD gets unreadable before the values get inaccurate (only exception: on a weak battery, the current drive in ohms range may fail early, producing garbage readings, even if the leads are open-circuit).

I really got bitten by a much higher-priced 3.75 digit autoranging multimeter that displayed "-3.785 V" or something like that in auto-range volts with -7V applied. When manually switchted into the 40V range, display was OK. Obvisously with the low battery the output common mode range of the input ampliefier (the 7106 don't even have such a thing!) was exceeded before the output voltage was low enough to trigger the range switch. The "lo batt" indicator of that meter was *NOT* turned on at that point. Utter fail! (I fail to remember the brand or model, though. The case was yellow...)
 

Offline Poe

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Re: EEVblog #813 - Mailbag
« Reply #44 on: December 31, 2017, 07:54:50 pm »
Sorry for bumping an old thread, but I wanted to add some points regarding the cheap meter.

The small/large PCB arrangement not only improved PCB area usage, but also reduced the main board's copper weight to half ounce or less.  The small board appears to be 2 or 3 ounce copper for the current shunt.

Not that they needed that thick copper, the probe wires have fewer than five strands of 30AWG wire!  I had one with only three strands in each wire.   10A results in 5 to 8W of heat before the wires melt.

V-score is cheaper than routing, but even that would be too expensive.  Both of these boards are punched, including the plated through holes.


 


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