Recent Posts

1

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.  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.

2

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

3

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 pat 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?

Thanks
Joel

4

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.

5

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?

6

Beginners / Re: RS232 intermitted issue

« Last post by tzc24 on Yesterday at 11:52:04 pm »

You can try a different terminal emulation software, such as PuTTY or HyperTerminal, to see if the issue persists.

I have tried different terminal and unfortunately all come out with the same output.

7

Beginners / Re: RS232 intermitted issue

« Last post by tzc24 on Yesterday at 11:49:48 pm »

I had checked all the tx voltage there are no abnormality found.

8

Projects, Designs, and Technical Stuff / Re: Vacuum Fluorescent Display Driver

« Last post by bostonman on Yesterday at 11:49:09 pm »

I assume you mean the wires behind the glass?

Nothing seems to glow even faintly. Tomorrow I’ll reflow the pins, but I tend to go heavy with the solder regardless. A quick look earlier didn’t reveal any indication of bad solder or lack of, however, anything is possible.

Odd it was working and nothing more than a power recycle resulted in the display not lighting.

9

Projects, Designs, and Technical Stuff / SX1280: anyone?

« Last post by SiliconWizard on Yesterday at 11:48:44 pm »

Just wondering if anyone here has used the SX1280 in a project, any feedback would be welcome.

https://www.semtech.com/products/wireless-rf/lora-connect/sx1280

10

Test Equipment / Re: Heads up on MicSig Probe

« Last post by J-R on Yesterday at 11:46:52 pm »

Looks like it is actually a "SainSmart Official" store-wide sale.  So be sure to check out their other items if you have money burning a hole in your pocket...