Recent Posts

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Projects, Designs, and Technical Stuff / Re: Heated Ferrite == Useless Ferrite

« Last post by mag_therm on Today at 11:17:18 am »

Refer to Fair-Rite "Product Life"
When re-using salvaged cores, it might be necessary to know at least whether it was a MnZn ( low freq, power transformer etc), or Ni Zn (high Freq)
Both types can be damaged by excess magnetic field strength H swing   and mechanical stress , NiZn may be more susceptible to those.
Both types should recover after being heated above Curie Temperature.
MnZn Cores usually work most efficiently  at around 90 C There are graphs for the material types showing this. So design for 70 to 80 C helps counteract thermal runaway effects.

For hobby here I have hand wound about 20 power transformers, and  inductors using surplus  (new old stock) MnZn cores from electronics surplus suppliers.
For components in the 10's MHz range needing NiZn I would always buy new cores. I have had good success just using basic design methods although some I have done with FEM.
I hav e FairRite Type 61 toroids running at 14MHz as power transformers for ham radio. They run too hot to touch, and they are efficient enough. It is a  bit difficult to measure temperature and performance in situ  at that frequency.

If a new core set is around $2 I wonder why salvage attempts  would be worthwhile.

2

Metrology / 20khz instrument amplifier with 1000X gain - or some other approach?

« Last post by veeti on Today at 11:12:57 am »

Hello

Any thoughts to interface with torque sensor which output is highspeed differential signal (few millivolts aprox 20khz)?

Or atleast that is the way I figured out how to use this kind of sensor, inside electric bicycle?
There was samekind thread https://www.eevblog.com/forum/metrology/reading-a-magneto-elastic-torque-sensor-with-high-resolution/ in few years ago - but the post seem dead, so I started new one.


But like in the old thead the sensor has two identical coils, each with 15ohm resistance - and one end connected together.
Inside the coils is foil  which has cut outs, mirrored to eachother. My gues is that when the foil is twisted by torque the cut out somehow move to increase one coil impedance and decrease the other.

The problem is that even I  apply quite a lot torque, I can only measure few % variation in my test circuit.
Example without torque I have 300mV difference, with all what I can twist with couple of big wrenches I get 294mV

The frequency has to be high so that the skin effect causes the foil only to affect the measurements.



Can I just put instrumenal amplier? with 1000X gain to get few volts output?

And another question, can I supply the coil with sinusoidal DC - or do I have to use AC. DC just would make easier for power supply setup 

3

Beginners / Re: Why are thermal jumpers so expensive?

« Last post by tooki on Today at 11:09:40 am »

Next question:

What are the most common ceramics used for SMT resistors?

It looks like AIN is a fairly common ceramic for thick film stuff.

AlN only used on very high-power ones. Most are alumina, and cheaper ones unspecified “ceramic”.

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General Technical Chat / Re: A serious (as in not troll) requestfor help w/ultrasonic transducer

« Last post by watchmaker on Today at 11:09:33 am »

I'll be happy if you find something that can extend the life of these machines. I just want success for people's endeavors here, nothing owed lol.

Engineering used to be about problem solving, figuring it out. Like doing a crossword puzzle. You never worried, just kept chipping away and learning. Some searching, the right keywords and I can somewhat understand the machine enough to help a bit. Physics, MecE, EE (multidiscipline) knowledge needed for this Tempo make it difficult.

Today, young engineers literally have a panic attack if they don't know something. There seems to be a stigma with "not knowing", even in business and management. I find it funny, being free of such worry. Electronics gives a constant humiliation for those types of people, the "know it all" types especially.
If you don't know enough, then ask - I've learned to reach out to manufacturers and sometimes they have great expertise.

I am so frigging tired of people who WANT to fail.  So I passed on your post to both of the service businesses; the one responded saying emphatically that you cannot buy donuts!  Have not heard back from the person who actually bought all of L&Rs inventory.  He is likely much more confident.

That is what people told me before I had all the breakable parts for the Hamiltn M21 made and 100s of mainsprings for my bread and butter aircraft clocks.  Paid those back 5 times over in the last 30 years.

Most people are too damned timid to seize an opportunity.  They say "no" when a life altering adventure is right in front of them.  In all my years, I have encountered very few ventures or adventures where saying "yes" resulted in my death.  Most of my regrets involve saying "no".

Fortune favors the bold.  While the meek may inherit the earth, nothing was said about the timid!

5

Projects, Designs, and Technical Stuff / Re: more modern version of tl494?

« Last post by xavier60 on Today at 11:06:04 am »

I read somewhere that newer TL494 ICs now have multiple pulse suppression to prevent noise causing unwanted toggling of the steering flip-flop. Has anyone confirmed this?

6

Test Equipment / Re: Choosing between entry-level 12-bit DSOs

« Last post by gf on Today at 11:00:55 am »

The Rigol is applying the theory correctly and the Siglent can't possibly be doing an infinitely wide reconstruction, so... 

But you have the choice to implement either

• a truncated/windowed sinc filter with a n*sampe_rate...(1-n)*sample_rate transition band (symmetrical around 0.5*sample_rate),
• or an ordinary steep lowpass filter with a n*sampe_rate...0.5*sample_rate transition band,

where 0<n<0.5 (for example n=0.4).

Contrary to what you might intuitively believe, it's the latter which does what people here seem to expect when it comes to frequencies beyond the filter's reconstructability limit of n*sample_rate. But it requires more DSP resources.

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Projects, Designs, and Technical Stuff / Re: role of optocoupler for biasing drain of amplifiers

« Last post by john23 on Today at 10:58:41 am »

Could you please draw the mosfet and amplifier with the devices ?
I am having trouble to imagine your words.

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Test Equipment / Re: Choosing between entry-level 12-bit DSOs

« Last post by Mechatrommer on Today at 10:53:50 am »

this is +1 imho in rigol, lets not forget, the 2 scopes discussed here got pros and cons.

Since the Siglent can into 2 Gsa/s, it could potentially be modded to support at least 800 MHz single-channel bandwidth, if there are no further limitations in digital signal processing and/or software. I don't recall anyone mentioning or trying this though.

i posted this earlier in this thread, some people said its very rare case. now we have 2 person asking for it so i'm not so rare, lets wait HAM fellows (names with numbers and who build their own radio) to chime in what they have to say, cheers.

9

Beginners / Re: Convert US standard 115V to International 230V

« Last post by radiolistener on Today at 10:50:55 am »

I believe the OP is just not qualified or certified and should not be making this type of decisions.

There are too many unknown variables and the OP is, clearly, not qualified. A medical device sold professionally and for export and this is how it is being designed?  In America? Really? Nobody thinks there is something wrong in this scenario? Really?

Completely agree. I wanted to politely bring the topic to the point that this is not easy decision for medical devices, because there are too many pitfalls which is not visible for non medical devices staff, but it appears that discussion going into wrong direction and my attempt was failed. Unfortunately some users decided that since they see simple and easy solution, they can just ignore medical devices specific and advocate their solution as the best solution and fiercely rejecting and criticizing all arguments against.

10

Beginners / Re: Why are thermal jumpers so expensive?

« Last post by tooki on Today at 10:45:26 am »

AFAIK AlN ceramic is used for ceramic knifes, though the requitements on the material could be a little different.

Nope. They’re zirconia (zirconium dioxide).