Recent Posts

1

Other Equipment & Products / Re: Different bases on Amscope microscope

« Last post by KE5FX on Today at 11:40:21 pm »

Any time you bump them the microscope shakes for ages.

So don't do that.

The trouble is you bump it every time you touch your face to the objectives.

Not an issue in real-life usage.  At higher powers, sure.  But for SMD work?!  C'mon.

Meanwhile, the ability to put the microscope exactly where you want it, instantly, at any height desired, with near-zero effort, as well as to swing it away completely when desired, is a game-changer.

2

Repair / Re: Desoldering advice

« Last post by strawberry on Today at 11:39:13 pm »

lead solder. 80W should be minimum
if relay do not operate and coil is not open then something is wrong with control circuit

3

General Technical Chat / Re: Russia and China to Build a Nuclear Plant on the Moon.

« Last post by vk6zgo on Today at 11:35:40 pm »

The moon doesn't rotate, so no night or day.

Of course the moon rotates. Once a month.

The dark side of the moon is a music album, not any description of reality.

Which was what I meant to convey, but stuffed it up.
I was thinking about how the moon presents the same side to us, & that there was always some part of the moon lit by the sun.
I neglected the fact that we don't see all of the same side, all of the time.

4

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

« Last post by Mechatrommer on Today at 11:34:34 pm »

900 switches when all 4 ch on and MSO

I see. Yeah that's kinda expected.
A hacked 800 doesn't do it, it stays on 312.5.

you havent activated the LA in your video. if that D (with number 1-16) button on the bottom screen becomes green and you have many horizontal green lines on the screen, then your sample rate will become halved again iirc (156.25MSps)

It however starts to fail well below Nyquist (which is 156.25 MHz at this sampling rate): the displayed signal begins to have lower frequency noise at about 100 Mhz and it becomes next to useless at ~130 MHz.

sin(x)/x will start to go wrong at sample rate / 2.5

1) to be precise, anything more or equal to Sample rate / 2 will not be reconstructed correctly, i havent found literature saying exactly 2.5, i guess 2.5 figure is just a safer bet from scope manufacturers for Sinc interpolation to be correct, or the right BW limit roll off for anything Sr / 2 and higher to be suppressed to an acceptable level. iirc even signal with Sr / 2.1 can be reconstructed correctly, given the condition... "thou shalt not have any harmonics (higher frequency elements) equals to or more than the sample rate / 2, not even the slightest" which comes to the second statements.

2) we usually try to prove Sinc failure with fundamentals or pure sine signal very close to Sr / 2 but infact if front end BW is not brickwalled at sample rate / X ... (X > 2, eq 2.1, 2.2, 2.5 etc) Sinc will still produce "not exactly the original" signal on screen due to presence of non zero harmonics above nyquist limit, even if fundamentals is way below the limit. its just its not so obvious when harmonics magnitudes are small. a good example is low frequency square wave signal but very high rise/fall time, on larger time scale it seems ok, until we zoom closely into the rise/fall time portion.

so please bear in mind Sinc inaccuracy doesnt only happens at fundamentals near nyquist limit, what matters is the highest frequency content presence, the bigger the magnitude the worst the reconstruction will be. thats why some people swear by the "properly BW limited" scope.

unfortunately they sometime wreak havoc from reality, if your circuit is already BW limited (no oscillation) then it should be fine... but if you expect your circuit to contain higher harmonics at significantly high magnitudes and you choose to probe with <= Sr / 2 anyway, then imho its you that have problem, not the scope. otoh built in properly BW limited scope will not be able to sense circuit misbehavior above Sr / 2, everything will just look fine, until the problem manifests/propagates itself on another portion of the circuit. fwiw.

5

Projects, Designs, and Technical Stuff / Re: How is a motor run capacitor sized?

« Last post by johansen on Today at 11:33:12 pm »

Size and cost constraints.

A 35uf 63vdc 40vac rated film cap is 10$

6

Projects, Designs, and Technical Stuff / Re: PC74hct4046ap Replacement

« Last post by Benta on Today at 11:29:00 pm »

You're barking up the wrong tree here, I think.
Issues with the '4046 are generally related to the PFD.
In your case, the '4046 is only used as VCO, where it's quite good.
If you have jitter problems, they're more likely caused in the "Custom Chip".

7

Test Equipment / Re: Hacking the Rigol DHO800/900 Scope

« Last post by mrisco on Today at 11:27:20 pm »

Yes, it is real   

8

Manufacturing & Assembly / Re: Vacuum Pick-Up Tool for Rework (Includes video of my own design)

« Last post by thm_w on Today at 11:27:17 pm »

Has anyone come across any decent pick-up tool for components?

Use the magic words "luer lock". This is the fitting used between needles and syringes. It's very popular in hospitals, but also used for dispensing solder paste, glues, and all sorts of other liquids. You can buy both straight or bent needles for very little money, and the rest can easily be made from parts lying around. (Except for the vacuum pump).

Did you read his next statement to understand the context of the thread? Or watch the video that he made, from 2019...?
"Has anyone come across any decent pick-up tool for components? I see there is the Yihua 850A(II) and the high priced Weller KDS806V. Am I missing one that's worthwhile?"

He was talking about the whole product.

9

Beginners / Re: Replacing SRAM IC with Flash

« Last post by VEGETA on Today at 11:24:37 pm »

Yes.  Specifically, you'd put a pull-up resistor from each of the A15, A16, A17, A18 pins to 5V, maybe as high as 1MΩ each? And also connect them to the four wiper pins of a 16-position absolute encoder like Bourns PAC18R1-33D28F, and the fifth pin to GND.

i thought of pulldown the 4 pins to have initial address bank of 0, please check attached initial rough drawing for the whole suggested system.

also instead of encoder I tried counter IC idea with one push button, gonna be a lot cheaper and smaller.

Another possibility would be to use a small microcontroller, for example a dirt cheap ATTiny404 (that you can program with an UPDI programmer using your freestanding C/C++ code developed in the PlatformIO environment), powered from the 5V supply line, with four of the microcontroller pins connected to the SRAM A15, A16, A17, A18 pins.

going MCU is a no-go for me since i won't be getting the production boards here to my country (Jordan) due to excessive customs charging and the complicated stuff I need to do. All my other products which are being sold now come from PCBway directly to my shipment and fulfillment company (Next Smart Ship) which is linked to my store... then I ship with press of a button.

having MCU will need PCBway to program them which is something i never tried and will for sure get some problems.

I also thought of using pi pico MCU and put the complied code on my website for the end user to download and program himself using his own computer. will work but prefer without MCU if possible.

If you use a binary counter like 74HC393 instead of a microcontroller, make sure you have a low-pass (debouncing) filter on the button connected to the clock input.  Otherwise a single press may jump multiple banks.

a 1nF ceramic would do i guess. could go up to 100nF if needed.

As to the battery, I haven't thought about exactly what kind of circuit is needed.  A simple (Schottky) diode would protect the battery from being backfed by 5V whenever it is connected and powered on; but something like a MOSFET that would disconnect the 5V line when no 5V power is present, and disconnect the battery when 5V is present, would reduce the load on the battery through the pull-up/pull-down resistors, and ensure the battery would not try to power the microcontroller/counter if one is used.

I would need to open the OEM memory card and check voltages and continuity...etc to have an idea what is there.

I made this: https://thundertronics.net/product/dreamcast-advanced-controller-board/

which is more complicated and I maneuvered around it by using 5v rail as input then bypassed entire old battery to have it to work, and it did.

designing a simple rechargeable solution which uses small LIR2032 battery should be no problem.

having a parallel fram\mram non-volatile 512kx8 would be around 30$ for the ic, it is a no go!

Expensive?  I count less than 10€ in parts, either way.  If you or a friend has a 3D printer, you could print a custom enclosure, too.

best price to sell these would be 50$, not too little and not greedy.

I guess if counter ic + button works instead of 3$ encoder then this would reduce the cost nicely. pcb gonna cost too... but as you said i will go with 3d printing + shiny laminated label on top which is going to be good enough.

how much bom cost do you expect after this?

10

Beginners / Re: Basic PLC Analog Input Question

« Last post by BeBuLamar on Today at 11:23:17 pm »

The input of the B&R X20 which is like most other PLC's system. It expects a voltage which in your case from -10 to +10V. The sensor you have is just a resistor and it doesn't generate any voltage. You would have to somehow convert the resistance of the FSR to a voltage. Perhaps part of a voltage divider? Still you will have to do quite a bit of calculation within the PLC because the voltage won't be linear to the resistance of the FSR.