Rack'em Up! DIY 19-inch (ish) Racks for T&E Equipment

      Necessity is the mother of invention....

  A somewhat similar parallel to this might be "tight spaces are the mother of... cheap alternatives" ?!

  Ok, so we all have this "situation" where equipment we buy starts flooding our workspace until you literally are stubbing you toes against them even getting up from your chair.

  Same thing happened me (the flooding part, not the toe stubbing part) so having observed some narrow  spaces  in my workspace, I decided the best way to organize things would be some (only 2) racks.

  Easier said than done.... My workspace is at the second level of the house, up two flights of stairs, one more steep than the other... also the last set of stairs is this weird spiral thing, so you can imagine a normal 19 inch rack  is impossible to haul  up there.

Huh, should see me hauling VNAs and Optical  analyzers up those stairs... my god, that's a laugh for anyone....

  But I digress. So, why not have a rack in pieces and assemble it upstairs.  Wel, how about I up one on this one...  how about I make my own cheap rack system... OK, cheap-ish.

 The big rack, in all its glory

  The structure is made from 2mm thick, 40mm wide angle iron.... A keen eye will see that the dimensions are slighly bigger that the standard 19 inch racks system.. that's because my equipment does not all have the rack handles, so I wanted an wasy way to get my hands on the sides of the equipment to get it in and out of the rack.

  Hence, I came up with these measurements (more out of chance than maths and intent, but hey...) 61.5 cm deep x 56.5 cm wide or 24.2'' x 22.2''

 This is enough so that I can man-handle units in and out of the rack, including big lumbering things like an Advantest optical spectrum analyzer that weighs the equivalent of a medium-sized anvil... and is just as nasty to handle.

  Also, the racks are on wheels so they can be moved around. The big one, though, is meant more to just sit there and look pretty than be moved around. The shorter rack was designed with mobility in mind. Meaning, it's supposed to take equipment that is needed for whatever measurements I'm doing and sit next to my desk. After I'm done, it goes back to it's corner and out of the way.

   The shorter rack I made

                                The DUT shelf on the mid-height rack, sitting next to my desk. Really                               handy for measuring stuff and having a nice clean desk

      

                                             The stand for the DUT with its rackable mount

  And it works pretty well in practice. I also added a nice "porch" for the DUT to sit on when doing measurements or for a scope or whatever else is needed. The "porch" can be moved up or down easily as it has this really nice and fast mating system.

Tell us the price, son...

  So, the tall rack cost about 270 Euros, that's including wheels, all the angle iron, screws (which there's a boat load of), plywood and cross-braces. Ok, I know that there might have been a chance to actually get a cheap 19 inch rack at auction that's somewhere around this price, but because of the logistics of getting one delivered to my home, I just couldn't be bothered. Plus, I made a rack all by myslef... how cool is that.

 Ok, it doesn't look like something you'd write home about, I know.... but considering that the tall one is now holding in excess of 250 kilos of equipment and is stable and still moveable is something to note.

  Price aside, this was also the first rack I made, so once I started building, it took me something like 3 afternoons (as in about 3 or 4 hours every day) and 2 whole days (meaning a Saturday and Sunday) to have everything together and stable. Once I had my head around the whole thing and knew how everything should go together, the second rack took only a whole weekend to cut, screw and assemble.

                                  One of the shelves. Board in the upper part and the two
                                               cross braces made from steel T profiles

         Why not those modular aluminium extruded profiles, I hear you ask ?

  Well, turns out that a) they're  kinda expensive and b) it's a real hassle to figure out all the bits and bobs you need to put everything together. For the tall rack, my calculations stopped at around 250 Euros for the 4 vertical legs, wheels and 4 rafters. Adding to that another 150 Euros in things to keep everything together and I started to look for altenatives. The end result may not be as sexy, but it does the job and I get extra "cool" points.

  Hope you enjoyed this and maybe it inspires you to get cracking on your own thing. And if you do, please make it pretier than mine... and share some pics.

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Counterfeit 3045 low noise LDOs from eBay

   

    Sometimes lazyness gets the better of me and I tend to look for an easy way out or an easy fix to stuff. Buying ready-made boards from eBay is one such way, but in this case, it ended biting me in the ass.

   I have a project where I want to have some voltage references and other sensitive experiments into an enclosure and also have a really low noise  LDO to power them, in the same enclosure as the rest. I thought that some LT3042/3045 would be ideal. Instead of making my own boards, I thought why not buy some ready-made ones from eBay

                                                    My future-to-be experiment

   So I bought two different boards. One is a really crappy looking one with what can only be desribed as the world's crustyest capacitor. Fun fact.... the blue cathode markers on the rectifier diodes is actually done with a marker or sharpie. How do I know? The marks disappearead after I put a bit of alcohol to wipe away some rosin on the board  :|  

LT3042 board

       Crappy looking input capacitor. It's light as a feather and came already swollen. 

   Crappy looks aside, the LT3042 on this board looks genuine. It has the right markings on the case "LTGSH", which according to the Datasheet , is the right one for the MSOP package. 

OK, so far so good...

   But I needed another LDO. And I wanted another design, just so I can, at some point, try to measure their noise against a real LT3042 board  (which would be designed by me, but somewhere in the future,  or so I thought) and see which one (mine, of course) would come out on top as having the lowest noise.

   I give you specimen no.2, which, after making its way from Saudi Arabia, of all places, it ended up under my attentive (not really) gaze.

 At first glance, looks legit and much cleaner layout that the previous dog's breakfast. But unfortunately the devil is in the details....

                                                        LT3045 board AKA specimen no.2

    On attentively looking at the LT3045 Datasheet  we see that there are two variants of the chip....one with 10 pins in a DFN package and another with 12 pins in an MSOP package. But someone in China was thinking, and, as you can see from the above picture, they decided to do away with LT's wasteful marketing B.S. and just have a  DSN package with all 12 pins on it. Brilliant! 

  Only thing is, I actaully wanted an LDO that really is low noise and something tells me this one is not it.

   I am working on an LNA set-up to measure voltage reference noise and will also try to measure the noise of these boards and compare them to one I will design myself, because there's really no other way to ensure I really have the expected performance.

 

   Bottom line is, when it comes to these low-noise LDOs, 75 percent of the performance is actually in the board design and I am highly doubtful that the ones on sale on eBay are actually designed by someone that gave a sh$%^t about "low-noise". The other 25 percent is actually getting a chip that is the real deal. So just be careful what you buy and hopefully I made you wary enough so that you don't waste your money on useless junk.

Hope you found this info useful. 

Have fun with your projects

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