Recent Posts

1

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

« Last post by T3sl4co1l on Today at 11:25:38 am »

Unitrode had advanced replacements for the TL494, but after Texas Instruments bough them their selection guides were removed.  I think they had a current mode control version of the TL494.

UCC3808 is kinda like that, but a stripped-down (8 pin) version, not as flexible.

Tim

2

Test Equipment / Re: Standardised Way To Test Oscilloscope Screen Update Rate

« Last post by RoGeorge on Today at 11:21:35 am »

With mouse plugged into the scrope the scroll wheel is available for making numeric field adjustments.

That's interesting, must not have implemented that in the web interface

An USB mouse only sends the displacement+buttons when polled, and the standard HID poll rate is something about 100Hz (don't recall the exact rate, it's in the HID specs).  That is low enough to affect pro gamers, so there are non compliant USB ports, and non compliant USB drivers that can poll a mouse at 200Hz or more.

Another thing, LCD panels are very hard to drive at fast refresh rates, and they are usually working at less than the CRT used to.  Most LCD and/or IPS panels are at 50/60Hz refresh rate, yet they do not flicker to the eye (like a 50/60Hz CRT would), because of the remanence.  Flat panels are very hard to drive at more than 200Hz, and gaming monitors at >150Hz are very expensive.

My guess is the refresh rate in an oscilloscope panel would be a casual 30 or 60Hz, I don't see why I would need more than that, but I didn't measure.

3

Beginners / Re: The old "Replace blue LEDs with red LEDs" 7 segment question (74HC595)

« Last post by pcprogrammer on Today at 11:20:17 am »

I have some doubts though, as I can see on the layout that it appears that the IR supply is just a 3V3 Zener diode dropping the 5V line.
How much current can a small SMD Zener usually handle?
>1A?

It is not so much as to what the zener can handle, it is about the series resistor dissipating the remainder of the voltage. The zener is biased to some current and can keep the voltage in check as long as the current drawn stays within limits. To be able to use the 3V3 made this way to drive up to 300mA the resistor needs to be 5.6 Ohms and the zener must be able to dissipate about 1 Watt of energy when no current is flowing into the displays.

Most likely it will not be designed for this, so not a good idea to start using this supply for driving the displays.

A series diode or two in the common connection of the 7 segment displays, like SeanB suggested, might be an easier solution.

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Beginners / Re: How Current Limitation is happening in the circuit???

« Last post by MrAl on Today at 11:20:13 am »

It is not an auxiliary coil that is used for deriving 5V for volt amp meter.


From the main transformer after full wave rectification,  I have used it.

I want to derive variable power supply up to 30V and current limiting adjustable up to 5 amp.

Here is a cleaned up drawing.  You should try to post drawings that are very clear so people can help easier.

As mentioned by Xena, there is a short in the diagram indicated here by a red "X".

Also, you seem to be suggesting that there is only one transformer.  In the new diagram the way you have it connected, are the transformers T1 and T2 actually two different transformers or are they the same?  Alternately, is T2 just a separate winding on T1 perhaps?

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Beginners / What size Teflon sleeve tubing are you using for 1/4 - 1/2 Watt Resistors

« Last post by Johnny10 on Today at 11:13:36 am »

What size Teflon sleeve tubing are you using for 1/4 - 1/2 Watt Resistors and where are you buying?

Thanks

6

Microcontrollers / Re: Divide clock by 3 on a ATF16V8B

« Last post by langwadt on Today at 11:07:04 am »

Can you please tell me if this is doable, and how could I do it ? I can access to a Windows computer if needed.

Yes it is doable, with the caveat you have a 1/3 or 2/3 duty as mentioned above.

You need Wincupl, to compile boolean equations to JED and then a Device programmer to pgm the 16V8.
WinCUPL can run command line, which may help portability ?


If all you are doing is /3, you could look at other CMOS programmable dividers ?
eg the widely available HC161/HC163 can divide by 3 with an upper Qn connected to /LOAD, so the counter goes 14,15,0,14,15,0... for divide by 3.

Addit: If size matters, you could find a small MCU that has a CLK out option with /3 choice. Still needs programming, but it will be smaller than a 16V8 or CMOS counter.

double* and divide by 6?

number 4, http://xilinx.pe.kr/_xilinx/html/tip/sixeasypieces.htm

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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 11:06:38 am »

Hello XVR,could you give a practical numerical example with Tja & Tjc expression so i could see in what cases my MOSFET will be burned?
Thanks.

8

General Technical Chat / Re: Dumpster diving save VFD

« Last post by Miti on Today at 11:05:30 am »

From what device was it recovered?

Don’t know what it was. Check Noritake site.

https://www.noritake-elec.com/products/vfd-display-module/built-controller-vfd

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Computers / Re: Format a 256GB pendrive with FAT32 using a windows 10 pc

« Last post by m k on Today at 11:02:20 am »

128 used to be legit sector size.

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Projects, Designs, and Technical Stuff / Re: Build or buy? Multi-level vessel temperature logger

« Last post by mianos on Today at 11:01:12 am »

The term for the tube with a closed end is call a "thermowell". Normally they are stainless. The ones for brewing can be very long, 30cm. You can pick up all sorts of them from aliexpress.
Then, as BennoG says, I'd stuff a bunch of probes down them. Personally I'd much prefer proper 3 wire pt100 probes, you can also get them from "funny bunny"'s store.
He has the ones without covers, they are pretty easy to work with mechanically as the junction is only a mm or so. That would be very easy to wire and stuff.

This said, the normal MAX31865 is an spi device and you only get one probe per chip.  (I have good multiple board esp-idf drivers if you go this way and want them).

Your other option, DS18B20 would be much easier, they can all be run straight to your MCU with no driver board, they are quite precise. With .5 degrees of a PT100 based on my experience using them quite a bit. (They need pullups btw). The biggest down side would be getting a lot of them in a thermo well. 

ps, 0.1 is quite easy for the pt100. That's why I aim for.

I also have a pt100 on a bonded teflon tube. You could just fix these together and pull them apart for cleaning. Food safe, acid safe to the max. Not safe amongst forever chemical fear-mongers, unless you want top go past 550.