Recent Posts

1

Test Equipment / Re: Siglent SDS2000X Plus - Bugs / Missing Features / Feature Requests

« Last post by KungFuJosh on Today at 12:41:09 am »

Is there a reason the screensaver doesn't shut off the backlight? Doesn't seem like it's doing a lot of saving if the backlight is still on.

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Beginners / Re: Decent but cheap Trinocular stereo microscopes for soldering

« Last post by Doctorandus_P on Today at 12:28:56 am »

I bought an Amscope (clone?) from Ali a few years ago, Price including shipping was around (below?) EUR400.

If you are cost sensitive, but can make things yourself, then I recommend to buy the microscope head only and make the rest yourself. Accessories are relatively expensive, and not of very good quality. Just the Z-adjustment for example costs around EUR65, a simple stand (which I bought) around EUR100, and the big boom thing itself is a few hundred EUR. Just have a look at what the parts cost on Ali. They are also sold separately.

Handy parts to have are a 0.7x Barlow lens (I have a 0.5x, but now the eye pieces are quite high above my desk. Also get yourself a ring light with an integrated glass plate. This protects the lenses from solder fumes and spatter. When you use a (replaceable) Barlow lens, this is not very important, but if you want to use it without a Barlow lens the underside of the microscope is open (or at least add a piece of glass / filter there.)

I bought the simple stand "to get started", and with the Idea to make a more luxurious stand myself, probably with MGN12 rails, and very likely some stepper motors. If you put stepper motors on both the Z-distance and zoom, then you can write a simple microcontroller program that takes two potentiometer inputs. One for zoom, and one for focus, and then when you change the zoom, the uC keeps your object in focus by also adjusting the Z-height. Uc also can adjust the light. There is a very big difference in brightness between zoomed in and zoomed out. The difference is big enough to be (slightly) annoying, and I tend to adjust the brightness when adjusting the zoom level.

When you DIY, a built in fume extractor is also nice t have.   

3

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

« Last post by soldar on Today at 12:25:14 am »

I asked if the design would have to be marginal before there was a problem? And you replied, yes, the design would have to be marginal. So I don't see any disagreement here?

To avoid generalization, the power supplies in this case are specified with an input rating of 85 - 264 V AC or 120 - 370 V DC, and an AC frequency range of 47 - 63 Hz. There is also a derating curve for low voltages. It is to be assumed that they will perform to specification.

One other thing, the equipment which is the subject of this thread is not a medical life support device, it is something along the lines of an advanced gym machine, somewhat akin to a sophisticated treadmill. There is no danger to life or limb if it stops working for any reason.

We are in agreement in everything.  I was not referring to these specific PSUs but rather to a general statement that voltage or frequency do not matter ever. That is too broad and needs some qualification. I am well aware that it has been determined the PSUs in this case do not need any adaptation.

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FPGA / Re: Analog video output with FPGA ?

« Last post by BrianHG on Today at 12:15:05 am »

HDMI to VGA adapters, basically a dime a dozen....:

https://www.amazon.com/HDMI-to-VGA-Adapters/b/ref=dp_bc_aui_C_5/137-1730865-9692944?ie=UTF8&node=14570285011

Some tested recommended adapters:
https://www.retrorgb.com/hdmi-to-vga-dac-analysis.html

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

« Last post by IanB on Today at 12:11:40 am »

I asked if the design would have to be marginal before there was a problem? And you replied, yes, the design would have to be marginal. So I don't see any disagreement here?

To avoid generalization, the power supplies in this case are specified with an input rating of 85 - 264 V AC or 120 - 370 V DC, and an AC frequency range of 47 - 63 Hz. There is also a derating curve for low voltages. It is to be assumed that they will perform to specification.

One other thing, the equipment which is the subject of this thread is not a medical life support device, it is something along the lines of an advanced gym machine, somewhat akin to a sophisticated treadmill. There is no danger to life or limb if it stops working for any reason.

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FPGA / Re: Analog video output with FPGA ?

« Last post by BrianHG on Today at 12:10:38 am »

If you want 8 bits per channel, look for the cheapest RGB video DACs and be done with it.  I know it's overkill, at these thing can run at +200Mhz, but it's easy and regulated outputs, with 75ohm cable driver built in with static immune outputs.

Try this guy:

ADV7125xxxxxx are still available at $7 to $9 USD a piece.  (search for alternate suffix as the 330MHz version I listed may be overkill)

ADV7123xxxxx are available at $5.37 USD, but you will need to buy 10 of them.  These are the cheapest if you go to ~25 pieces at they drop to $4.40 USD.

ADV7120xxxxxx are still available too, only 24bit, but more expensive and harder to find compared to the 30bit version above.  They seem to be available at $10 USD for the slowest 50MHz version.

THS8136xxxxx are available at $5 USD.
THS8135xxxxx are available at $5 USD.

Why not just output DVI/HDMI from your FPGA?  It only requires 8 outputs and only requires a 1$ IC if your FPGA doesn't directly support the TMDS standard through a cable, though, at 240p, even a basic LVTTL 3.3v IO with a few resistors can suffice.  If you then want RGB analog, then buy a cheap HDMI/DVI to RGB dac box.  Now you will get support for digital and analog using 1/5th the IOs on your FPGA.

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

« Last post by dj_holmes on Today at 12:10:37 am »

Some reference from the manual:

From input board the data goes into Custom chip, clock is recovered from the input signal, then converetd and fed into the Digital to analogue converter

8

Test Equipment / Siglent SSA 3021X... Ooops

« Last post by Joel_l on Today at 12:03:54 am »

Hi,

I think I accidentally overloaded the input to my SA one too many times. My input impedance is no longer 50 Ohms. It still functions sortof.

I took the input board out and started looking around. I saw a 49R9 resistor which I assume is the termination resistor, it actually measures fine. I it looks like there are some clamping diodes on the input path and they seem fine. the input cap measures at 1uF, seems OK. Nothing looks like it got toasty.

The first IC in the input path is U1 a 956p, the 49R9 resistor is after that component in the path. Makes me wonder if that is the part I damaged.

I can't find any info on what that part is, anyone here know? Has anyone found schematics for this SA?

After some research, I believe the part is a GaAs MMIC. Still can't find a datasheet for the 956P to be sure.

Thanks
Joel

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

« Last post by soldar on Yesterday at 11:59:21 pm »

I understand what you are saying, but surely the design would have to be very marginal before this had an impact on the following section of the power supply?

My point, as I said, is that You have to be very careful when making such very general statements. That is all. In most cases you can get away with it but you have to be aware of these issues because they can bite you.

Electrolytics degrade over time. Sometimes not much, sometimes a lot. About 45 years ago the company I worked for imported two machines from America. I went there to do the training etc and the machines were shipped here and installed in customers premises. Almost immediately one started giving problems and it turned out to be a faulty capacitor which was marginal in the USA but insufficient here. I replaced it not only with a good one of the same value but with a higher value. It was a linear PSU and headroom was tight. With 60 Hz it still worked, with 50 Hz it was starting to fail, with 400 Hz it could have gone on for years.

With tolerances, failures, etc. the question is whether you would say absolutely and with no qualifications to a medical life support machine manufacturer or to a Boeing assembly plant "yeah, sure, plug it in as it is, no problem".

Those machines needed some weird adaptations. Instead of changing the electric motors (120 v 60 Hz) we installed a transformer to lower the voltage from 220 V 50 Hz to 100 V 50 Hz because at 120 V they would overheat. And they turned slower so we had to change the pulley diameter and make it bigger. The entire adaptation was quite complex and a bit on the Mickey Mouse side of things. The minicomputer read the program from a paper tape which took forever. Good times.

The loss of headroom with diminishing frequency is something which most of times will not cause problems but the engineer must be aware if life or limb of Boeing shares are on the line.

In summary, you should be very careful when making general absolute statements. And doubly so with electrolytics.

To quote myself:

You have to be very careful when making such very general statements. A SMPS designed for 60 Hz will have greater ripple at the capacitor when connected to 50 Hz. Most of the time the capacitor will have enough margin but if the capacitor is very tight initially or if it loses some of its capacitance it could lead to problems.

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

« Last post by IanB on Yesterday at 11:57:06 pm »

Capacitor ESR decreases as frequency decrease and ESR increases as frequency increases. So whether it 50 to 60Hz or 100 to 120Hz it won't make any difference worth worrying about to output voltage ripple. This can be easily tested with any LCR meter with variable frequency. If your getting a huge change in value between 50Hz and 60Hz then the capacitor is nearing end of life anyway and needs to be changed.

Neither ESR, nor change in capacitance with frequency, has been mentioned as of any significance to the discussion at hand. So it remains puzzling why you keep introducing them?