More Cheap eBay Hardware Failures

Data points…

Another knockoff Neopixel failed in the usual way, after a few days of operation: the first W2812B chip in the string gave off intermittent and random flashes of pure primary colors, the second was dead in the water. Replacing the first chip with Yet Another Knockoff from the same lot restored the tube to good health.

Some oscilloscope probing revealed a pooched serial data output with no active pullup, so the output data rarely exceeded VCC/2 and generally wouldn’t be accepted by the downstream W2812B. Nothing to show for it, as I couldn’t be bothered to upload a scope shot. Maybe next time.

One of the counterfeit FTDI USB-to-serial adapters in another tube base failed after a few weeks of operation, with symptoms ranging from hangs while downloading the Arduino program to readback verify mismatches. Replacing the failed adapter and the knockoff Arduino Pro Mini with a knockoff Arduino Nano (using a CH340 USB interface, presumably not a counterfeit) from a recently arrived envelope restored that tube to good health.

All in all, those knockoff Neopixels have been a constant source of amusement; worth every penny just for the privilege of holding them up for ridicule. The “genuine” FTDI chips weren’t much of a surprise, but I am mildly surprised they work so poorly.

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  1. #1 by madbodger on 2016-10-07 - 10:15

    I like to share scope photos too, but my old TDS220 scope only offers parallel, IEEE-488, and RS-232 outputs. At its maximum speed of 19200bps, the serial port takes nearly 40 seconds to download a screen shot, and the basement computer insists on saving that BMP file as a text file, so I still have to rename it, copy it to the upstairs computer, and convert the format to something more internet-friendly before I put it online. I’ve considered buying a newer digital scope, but the name brands all seem to run windoze inside (and have a wretched windoze-flavoured UI: I like physical knobs like the analogue scopes I learned on), and the off brands look a bit dicey to be buying used gear (I continue to be too cheap to buy a new oscilloscope).

    • #2 by Ed on 2016-10-07 - 13:59

      Bitmap as text? Eeeek!

      Given that the convoluted script I use makes a bankshot off EPS on its way from HPGL to PNG, that’s surely close enough to text… and, yeah, 19.2 kb/s takes quite a while.

      One of these days, that old CRT will fail and I’ll be forced to think about modernizing that whole mess. I want something that saves data on a USB Mass Storage device, rather than depending on translation through a Windows-only driver. [mutter]

      • #3 by Hexley Ball on 2016-10-08 - 13:06

        I got tired of the dance that Madbodger describes, which I encountered when downloading images from a TDS350. Serial just did not cut it. So I made a small system that emulates a Centronics printer and writes the file to a USB memory stick.

        Used an LPC1768 “mbed” platform; with high-level libraries for the USB file system and a built-in USB hardware connection — it was just a matter of a day or two to code it. Probably could do something similar with an Arduino if that is your cup of tea.

        I use it all the time now. USB is really the way to go for portability and archiving. Convenient, and it really reduced the craving for a newer scope :-)

        • #4 by madbodger on 2016-10-08 - 13:46

          You think a lot like I do. I did try to bodge up a Centronics interface with a little ARM microcontroller in the hope that it would be faster, but I never did get it to behave. Apparently parallel port “standards” have a lot of varied implementation details. The breadboard was pretty ugly, as the parallel port is a DB-25 connector, so I found a ribbon cable DB-25 connector and stomped a Berg connector on the other end, then wired it to the breadboard with a forest of jumper wires. Do you have any clues on how Tektronix expects the strobe/busy and other signals to behave?

          • #5 by Hexley Ball on 2016-10-08 - 14:41

            Poking around the old code, here is what seems to be the drill for reading data from the Centronics port:

            The program waits for the scope to assert Select In (pin 17), indicating a transmission has started.
            The program then loops until Strobe is asserted by the scope (pin 1), indicating that a data byte is ready.
            The data byte is read (pins 2 – 9).
            The program asserts ACK/ (pin 10) to tell the scope that its data has been read.
            After 5 usec the program de-asserts ACK/.
            Loop back to step 2 to read the rest of the data bytes.

            Wrapped around this is code that times the reception and after 2 seconds with no more data it declares that the transmission is over (then moves to the USB file write routine.)

            My notes show that capturing a bmp file takes 5.1 seconds.

            Hope that helps. If you like, I can send you the code — is the webmaster email address on your blog good?

            • #6 by madbodger on 2016-10-08 - 14:56

              Cool, so I don’t have to do anything with the “busy” signal? I could code it up from that description, but the source would be nice and yes, that email address should be good. And getting the whole image in 5.1 seconds would be an improvement too. Writing a file that size to a USB drive or SD card won’t take long at all. Thanks!

            • #7 by Hexley Ball on 2016-10-08 - 17:42

              You are right, Busy needs to be handled as well. I missed this when glancing over the software, because Busy is handled in hardware. Here is what was done:

              The incoming Strobe signal clocks a flip-flop, setting its output high. That output is the Busy signal, returned to the scope on pin 11. The flip-flop gets cleared by ACK/ (generated as mentioned above). So Busy is asserted from the time the scope sends a strobe signal until the time the CPU finishes reading the byte and signals that event by asserting ACK/.

  2. #8 by Vedran on 2016-10-07 - 14:45

    If 100MHz works for you, Rigol DS1054Z is really hard to beat. Sure it’s a modest scope by today standards, but compared to CROs of 20 years ago it’s a beast :)

    • #9 by madbodger on 2016-10-07 - 18:22

      Heh, my 20 year old CRO is a Tektronix 7104, with a full 1GHz bandwidth. My 7844 is 500MHz dual beam. However, to get pictures of their traces, I have to aim a camera at the screen. I’ve been looking at the Hameg, R&S, Rigol, and Tektronix offerings. Note, the DS1054Z is a 50MHz scope (though it does have an attractive price and 4 channels). I’d have to go to the DS1104Z for 100MHz (at more than twice the price).

      • #10 by david on 2016-10-07 - 20:24

        The 1054z can be turned into a 100MHz 1104z with a few minutes of googling and a quick software hack. Bizarre but true…

        • #11 by Vedran on 2016-10-10 - 08:11

          Not so bizarre if you take it as a marketing ploy that it is. Difference in HW is insignificant, only reason to have 50MHz version is market segmentation. Home users won’t spend 2x money on a 100MHz version anyway, and any corporate who actually needs so small a scope won’t blink at the difference. So why not buy some love and free promotion by leaking upgrade codes (or not squashing the websites who provide them)?

        • #12 by scruss2 on 2016-10-10 - 20:30

          Not any more, apparently. Rigol USA put out a warning that newer 1054 units would be bricked in the attempt, and they wouldn’t accept warranty returns on them. You have to use an older and rather buggy 1104 firmware, too.

          • #13 by Vedran on 2016-10-11 - 10:27

            How can they be bricked by user inputting a pass-code? As far as I know firmware upgrade is not necessary, you just enter a code.Do you have a link to that announcement?

      • #14 by Ed on 2016-10-08 - 09:08

        Long ago, in a lab not too far away, we had a Tek 7104 with all the fancy plugins. I loved that scope sooo much… but, wow, these days a mainframe scope just doesn’t make any sense, other than as a room heater.

        • #15 by madbodger on 2016-10-08 - 09:57

          I actually did use a pair of my old 500 series vacuum tube scopes to heat the house for a few days when it was so icy the oil truck couldn’t make it up my driveway. Turning electricity into heat is 100% efficient, whether you’re doing it with electronics or a space heater. I do use the 7104 occasionally, as I can’t afford another scope that can do what it does (I could directly view the (attenuated) output of my 70cm HT if I wanted to, which still boggles my mind). But you’re right: for most things, the little TDS220 is quite sufficient.

        • #16 by Red County Pete on 2016-10-08 - 12:25

          I picked up an old HP 1MHz dual trace scope at a surplus shop several years ago. National Semi used a fair number of the beasts for the kludge-box test rigs back in the Widlar/Dobkin days. Haven’t powered it up lately.

          At HP, we usually used our own scopes, but especially in the ’80s and ’90s, we really would have preferred a Tek. Somehow, the HP scopes were really finicky about triggering compared to Tektronix. The HP digital scopes were a joy to use, but I never saw them on the surplus market when I lived there. (I see that Keysight is the name-de-jour for HP/Agilent instruments, with the usual 30% price differential for “HP Quality”.)

          • #17 by Ed on 2016-10-08 - 12:42

            Keysight is the name-de-jour for HP/Agilent instruments

            I’m still ticked off about that whole name thing: the PC division should not have kept the name for commodity hardware. I delete all over their censored!

            • #18 by Red County Pete on 2016-10-08 - 22:01

              It was pretty much a power play during the split. The computer & printer people had the profits and cash, while instruments, medical, and semiconductors had lots-o-people, but not the high amounts of money. As best as I can tell, the computing side (servers, services, printers and finally PCs) were quite profitable in 2000. I think they pretty well dropped to commodity stuff after the Compaq acquisition; that was a couple years after the split.

              The instrument side was in a bit of a drought; military cutbacks hurt, and the leading edge of the dot-com implosion hurt the other aspects. Medical was a cash-cow, and was milked sold just after the split. Semiconductors died when dot-com did, though I found it interesting that the head of semiconductors ended up the second CEO of Agilent. I knew him when he ran one of the IC product lines; he was always going for the “big win”, and managed to sell his vision even when it wasn’t well backed by reality…

            • #19 by Ed on 2016-10-09 - 10:51

              As always: Money Talks!

              That low hum you hear comes from H & P spinning up to synchronous speed in their graves. Their bearings must be pretty much shot by now …

      • #20 by Vedran on 2016-10-10 - 08:17

        That’s why I’ve said “If 100MHz works for you” :)
        But otherwise than bandwidth, they really crammed a lot of bells & whistles in a very cheap 4 ch scope.