Recent Posts

1

Projects, Designs, and Technical Stuff / Re: ESR meter with extended scale.

« Last post by iet on Today at 05:41:47 pm »

As you know, the ESR of a capacitor can react to the heat of your hands. And the result may not correspond to the actual value. In addition, to obtain the most reliable result, very reliable contact between the probes and the legs of the capacitor is necessary.
Therefore, a simple device was made to install and measure the ESR of capacitors.

2

Open Source Hardware / Re: ESP32 Ethernet, Wi-Fi & Serial Gateway

« Last post by tooki on Today at 05:41:37 pm »

Looks nice!

Some questions/comments:
- choosing to use the bare ESP32 IC is a bold move, because that means you have to seek regulatory certification yourself for the radios. (One of the big advantages of using an ESP32 module is that they’re already certified worldwide.)
- why USB mini-B and not USB-C?
- what are the two different Ethernet port versions?
- the datasheet has a typo, the RTC crystal should be 32.768kHz, not 32.758kHz.

3

Beginners / Re: Photodiode output emulation

« Last post by KrudyZ on Today at 05:41:08 pm »

This depends very much on how accurate you want to model the PD behavior.
The simplest would be to use a function generator and a resistor.
This works if your PD is zero voltage biased and your circuit can work with either side of the PD being at Earth ground as that's where your function generator ground will usually be at.
You are of course missing quite a few secondary effects of the PD, such as junction capacitance and non-linear behavior if voltage develops due to the TIA not maintaining the zero bias (during transients).
The latter also affects the accuracy of the current. To minimize the effect, you should set the output voltage of the function generator as high as possible and then adjust for the desired current by picking larger resistor values (ideal current sources have infinite source resistance and infinite compliance voltage).
That being said there are many PD configurations where what I described would not work, so we would need to see your schematics.

4

General Technical Chat / Re: ultra sonic transducers

« Last post by CatalinaWOW on Today at 05:39:58 pm »

Maybe you can test your prototype on dogs at a pound or other location.  The whole point is to quantify the range at which a known power suppresses barking.  That is the basis for determining the power needed at your target range.  The equation I gave assumes one over range squared attenuation.  Thick bushes will provide an additional large attenuation, but would need measurement to determine the magnitude of the attenuation.  Unfortunately for your problem the bushes will be less effective at attenuating the lower frequency sounds associated with barking, so the fact that you hear them barking doesn't imply that your ultrasound will go the other way.

5

Programming / Re: Linux Dependency Black Hole

« Last post by shapirus on Today at 05:36:23 pm »

PSA to all who want to develop software:
 * Do not use bullcrap like Python or docker

What's wrong with docker? It actually provides a way to create an abstraction layer to decouple the software in question from the host OS, thus helping to solve dependency issues, not to mention runtime context isolation.

* Avoid dynamic linking, link statically if possible, and therefore:
 * Avoid library dependencies like plague;

How does the latter follow from the former? If you link statically, you don't care about dependencies.

By using libraries, you avoid reinventing the wheel and avoid making dangerous mistakes. That's what the libraries exist for in the first place. Yes, there are potential security risks, like the xz case. Such cases are rare. By creating your own implementations of what would otherwise be provided by libraries you waste resources and create potential vulnerabilities on your own.

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Repair / Re: Quick repair project - Marconi 2024

« Last post by Lodekka on Today at 05:34:43 pm »

Just to add that replacement lcd displays for 2945 and 2030/40/50 series instruments are available in case anyone is looking. Try asking on the Marconi groups.io page for more details

7

Beginners / Re: Photodiode output emulation

« Last post by tggzzz on Today at 05:34:31 pm »

Does anyone know if there is a simple RC circuit that could emulate the current output of a photodiode? I wonder if it is possible to achieve starting from a function generator, pass it through an RC circuit, and then using the obtained current pulse as input to a transimpedance amplifier. Any suggestions are appreciated.

In the late 70s I did just that: function generator->resistor->transimpedance amplifier. Worked just fine for my purposes, i.e. measuring the amplitude of a 1pW to 50µW optical signal.

No idea whether or not it would work for your purposes depends on .... your purposes, oddly enough.

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

« Last post by Buriedcode on Today at 05:32:11 pm »

Regarding re-using old ferrites and disassembling them: I've had some success with solvents. Namely paint thinner/white spirit.  The silicone/rubbery stuff is unaffected, but varnish and tape residue will dissolve in 24 hours.  As for heat, I've used a hot air gun - the larger 2kW kind, on a low setting, far enough away so it doesn't melt the bobbin - but its very difficult to get it right, plus its a proper hassle handling the hot cores, so I quickly gave up that method.

The solvent has worked for all ferrites salvaged from ATX supplies, but more modern SMPS transformers - specifically the sammler ones - took a lot longer.

I got a joblot of small EFD20 ferrites off ebay years ago, and every so often I'll "pickle" a batch to separate them.  I only have a few projects using those, but they worked as expected (had to change the airgap on a few, or completely remove the gap entirely), although I had to measure the core parameters to make sure they were in spec.

9

Beginners / Re: Resistor ????

« Last post by soldar on Today at 05:31:33 pm »

The value wouldn't start with black unless the multiplier band was silver, and 180 would be BROWN grey black black.  The grey/silver band has a sheen to it that differs from the pigment bands so is probably metallic silver rather than grey.   Perhaps this color-balanced zoomed in view of it will help.

Its a tossup between:
   Brown (1) Black (0)  Black(0) Silver (/100) Black () = One ohm, with a mystery black final band (as black isn't a tolerance color)
and:
   Brown (1) Black (0)  Black(x1) Silver (10% Tol.) Black (250ppm TC) = Ten ohms, 10% tolerance 250ppm temperature coefficient.

You are correct, of course. I had a brain fart there. I blame it on the flu I am undergoing.

10

Microcontrollers / Re: How to create custom bootloader in esp8266

« Last post by tooki on Today at 05:29:33 pm »

They said they want OTA (over the air, i.e. WiFi, Bluetooth, etc) updating. So I don’t think they’re referring to the hardcoded bootloader’s ability to load from serial.