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 91 
 on: June 20, 2019, 07:32:36 07:32 
Started by Just4Fun - Last post by Magnox
Don't forget 'rejects' from legitimate factories, scavanged from their refuse or passed on by friends who work there.

Recently I've had a run of fake GPS modules from China:

  • Modules labelled and sold as ublox 6, which were actually salvaged and reprinted old ublox 5 modules
  • Fake/clone ublox 6 main GPS chips inside the modules
  • Ublox 8 modules with both a clone chip inside (which seemed to work as an 8 should) but with no memory inside the module

...me not buying GPS from China any more!

 92 
 on: June 20, 2019, 07:27:37 07:27 
Started by Just4Fun - Last post by TucoRamirez
it alreadi has his reddit story

https://blog.heypete.com/2016/09/11/investigating-fake-max3232-ttl-to-rs-232-chips/

 93 
 on: June 20, 2019, 06:24:05 06:24 
Started by Just4Fun - Last post by dennis78
I think it is for more reasons:

- some of (old)components are from closed  manufacturing stocks (industry from 80's, 90's, 00's) and there are good
- from recycling board  discrete semicondctors, some IC's (I got some ST ARM's with firmware )
- clones, some are acceptable, some not

I don't know why they make clones of cheap components.




 94 
 on: June 20, 2019, 02:50:18 02:50 
Started by Just4Fun - Last post by leptro
in the past years i have face to fake lm35, fake max6675 from ebay. but all other standard components ( atmel mcu, diodes transistor, ttl ics) was not affected.
I also buy from time to time from tme and mouser.

regards.

 95 
 on: June 20, 2019, 02:15:22 02:15 
Started by Just4Fun - Last post by Just4Fun
I was testing a 2-channels RS232 adapter for my FPGA board, when I saw this "miracle":



If any signal from the RS232 is at a positive voltage and the board is not powered, there is a leakage current to VCC that turns on the led (power indicator).

More, if a VCC = 3.3V is applied the board doesn't work for speed greater than about 300 bps.
Applying a VCC = 5V the board works as expected.

I've used a couple of SP3232E (marked SIPEX that should work @ 3.3V and 5V according to the spec, ah ah...) that I bought from Aliexpress more that one year ago and not used until now:



I really thought that they were fake RS232 IC... so I removed both the ICs and cleaned the pads...



Than I've ordered  a new lot of SP3232E from TME (www.tme.eu), and resoldered them



...and now the board works at 3.3V and 5V @ 115200 baud and without any "strange" current leakage when not powered...  Grin

Here the good SP3232E from TME (in the bottom) compared with the fake one from Aliexpress (upper in the photo and not soldered):



They look very similar but some differences are anyway visible...

Analyzing the behavior of the fake one, I thing that they are fake MAX232. They seem working at 5V, but the leakage current from the RS232 when not powered suggests not to use them at all...  Cry



 96 
 on: June 19, 2019, 12:55:01 12:55 
Started by Magnox - Last post by Magnox
I've had a very long break from electronics due to unfortunate circumstances, but I'm back now. First job... make myself a new PSU. That was easy (it was mostly just wiring up SMPS modules into an old SCSI CDR enclosure) but I wanted a fan speed controller in it. I made one with what I had on hand.

The only 'clever' thing is the use of an adjustable LDO voltage regulator as the output stage. It had never occured to me to do that before but it worked nicely. The regulator adds its own reference voltage to the output, above the voltage I give to its reference input. So, I get almost the full 12V (11.7V) into the fan.

  • Microchip PIC 18F1320 controller (ADC, PWM, internal 8MHz oscillator, and because I have a box full)
  • Temperature sensed in two locations with Microchip MCP9701 linear sensors (because I have a bag full)
  • TI 2.5V TL431 reference for the ADC (I might as well because... you guessed it)
  • On Semi LM2931 output regulator (because it is LDO, has an Inhibit pin and... yes, a tube full!
  • Linear voltage output to fan: completely off, or 4.5V (minimum PWM determined by experiment) to 11.7V
  • Files attached for the design (CCS C, KiCad schematic and PCB) and a schematic PDF.
  • Most values are not critical.

The PIC samples the temperatures on a timer interrupt, averages and adds hysterisis to stop the output being annoying, and produces a PWM output of the required speed. Of course, two-wire fans (I had a nice Sunon to hand) don't like PWM. A low pass filter takes care of that, followed by an op amp to buffer and multiply by two. That feeds the regulator which adds its reference and feeds the fan. Simples! I used a 2.5V reference for the ADC to give more useful range. A couple of resistors to divide the 5V supply would suffice really, but I had the v.ref's so why not.

When I thought of using the regulator, a quick search found that I wasn't the first (well, d'uh) but the example I found was clearly flawed and could not possibly work as advertised. Mine does. The CA3130 (because I found one) runs fine on a single rail and the output goes to ground, so the final output is below the fan's minimum (only the regulator's reference voltage added). The regulator's Inhibit pin turns off the output when I want the fan off, so it's not sat there with a low voltage on it.

The code really should be tweaked and recompiled for a fan's minimum running speed. It gives a full speed burst to start the fan up, then drops speed to where required. The temperature set points are of course for my kit as are the rate of fan speed increase for each.

The PCB was designed to fit a small space in my enclosure with a screw hole in the middle, and to be 'hand made'. It could certainly be better, but it was quick to make and it worked. The circuit is simple enough to build on veroboard. Note that there is just one wire link on the PCB, for the Inhibit line from the PIC to the regulator. I wanted it finished and couldn't be bothered trying to re-route for it. Apart from three reservour capacitors, all passives are 1206 because I can route traces under those and still hand make the board.

To give a little protection from all the switching noise inside the case, the temperature sensor wires are old CD-ROM to motherboard audio cables. They are screened three-core and I earthed the screen to the case. The MCP9301 regulators use the internal wires of the cable, with a 1uF 1206 MLCC (not shown in the schematic) soldered directly across the sensor's power pins right underneath the plastic case. A heatshrink wrap finished those off nicely. At the board end, a low pass RC filter helps keep things smooth.

 97 
 on: June 19, 2019, 07:35:22 07:35 
Started by vuknikolic - Last post by vuknikolic
CountrySerbia
Sitew2.vuknikolic.in.rs
Notehobby mcu/dsp projects, computer vision, RT signal processing, neural networks.
I don't know what i can bring but don't make any damage.
use to read and forum looks interesting.
mainly for hobby, and sometimes commercial project

 98 
 on: June 18, 2019, 11:52:00 23:52 
Started by zac - Last post by bigtoy
I've used some small LiFePO4 batteries from the Chinese company "Soshine" in a couple of projects. These have been single-cell nominal 3.2V cells. I've been pleased with them. Capacity has been approximately what's claimed, and lifetime has been good. I'm certainly a fan of LiFePO4; I much prefer them to LiPo (which I've also used).

 99 
 on: June 18, 2019, 06:02:46 06:02 
Started by gfull - Last post by Captain_Boblo
I have two of the Rigol 1054Z scopes upgraded to 100MHz.  I use them for surge and high-voltage work where I wouldn't want to risk my Keysight MSOX3054A. 

The deep memory function on the rigols is very useful, I normally set up a repetitive surge test and use the record function to capture hundreds of waveforms for a test run. 
One of the most useful free companion software for the Rigol is "bildschirmkopie", it allows automatic retrieval of screen shots from the recorded waveforms.   

http://peter.dreisiebner.at/rigol-bildschirmkopie/download.htm


 100 
 on: June 17, 2019, 07:27:17 07:27 
Started by mnasabir - Last post by Magnox
lol - the link works. But... copy it manually (highlight it all and click Copy, not Copy Link). Them remove the http part. Copying the link with Copy Link Location confuses the browser.

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