Electronics > Projects, Designs, and Technical Stuff
DIY Modular Test Equipment Project
void_error:
--- Quote from: pmc on July 13, 2016, 04:15:41 am ---1. You were looking for an alternative to DipTrace and free 3D modeling.
For schematics & layout, check out EasyEDA. From the little I've played with it, it seems to work. And it's free.
For 3D, check out OnShape -- a relative newcomer offering no-apologies parametric CAD for free. They claim to import step. Free accounts limit *private* documents. I like it, for what that's worth.
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Looked at EasyEDA too but it's online which kinda sucks.
For 3D modelling I'm using FreeCAD, and download the 3D models for parts from tracepartsonline.
--- Quote from: pmc on July 13, 2016, 04:15:41 am ---2. Maybe I'm just not understanding what you're doing. It sounds like a UI front panel, some stackable modules and a framework for making arbitrary other stackable modules. Then I imagine that means a UI panel can manage a mixed stack behind it. Is that the idea, or did I get lost?
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Yes, the UI board is the front panel and you can stack other modules on top of it, on the opposite side of the front panel, see older posts, I have an example of how two modules stack up in 3D.
--- Quote from: pmc on July 13, 2016, 04:15:41 am ---If I'm not completely lost, then here's a thought: (assume easy answers to fab questions and) arrange modules to launch their real-world connectors/terminals from one side (both?) and angled ~45deg forward. The result would be stacks with a UI panel on the "front" face, and behind that along the "side" of a stack, all the external connectors facing front-ish.
(You're placing connectors at top and bottom not sides - but maybe the constraints that lead that way apply more to stacking connections than to external connections?)
Or more simply just go straight out the side - at cost of requiring more directly perpendicular access to the side of a stack.
Something kinda like this, but with the knobs on the front and connections down the side: http://w140.com/tekwiki/wiki/File:Tek_211_front.JPG
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Thought about having boards plug in at a right angle but mounting everything in an off the shelf enclosure would be more difficult, so all the boards are going to be parallel to the front panel. That way if the stack becomes too heavy to be supported by the front panel only two L-shaped brackets bolted to the bottom of the enclosure would be required.
pmc:
--- Quote from: void_error on July 13, 2016, 09:29:44 am ---... so all the boards are going to be parallel to the front panel.
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Understood. I'm not understanding how boards will expose terminal connections. I do see the function gen arrangement with BNCs next to the UI/display - but that only works for the one board directly behind the UI. How would you connect stuff to a module further down the stack? Or did you have in mind just one _function_ per assembly, with one interface board directly behind the UI exposing terminals adjacent to the display, plus whatever stack of add'l boards that function requires?
void_error:
Initially I wanted to use ribbon cables to connect the modules to the UI, that's the reason for the shrouded headers, but I figured out shortly after that the waveform gen can be strapped to the back of the UI after finding those BNC connectors that stick out.
One function per assembly is the general idea I'm sticking with but there will still be the possibility to add more functions which comes with a few small drawbacks like having to use some extra wiring if the board is located further down the stack requires connections to the front panel or if the board is physically too large.
As an example, say we have the Lab Power Supply configuration. The connections will look like this:
[UI board] : [Digital Isolator board] - [A/D & D/A board] : [Lab Power Supply board]
":" means stacked
"-" means wires/cables are used
The main goal is to keep wiring to a minimum, I don't like things that have so much wiring they look like a spaghetti bowl.
In some configurations it's difficult or not practical or too expensive to avoid using wires/cables for some configurations.
Other options I was thinking about as far as add-on boards are concerned are the possibility to add a second display (for a dual channel lab power supply) and a keypad (quite handy for a waveform gen) but I haven't decided how they will connect to the UI.
For the waveform gen at least the third layer of the stack (first one being the UI) will consist of the power supply modules for the different voltage rails required.
prasimix:
Hi void_error, this is a great step towards defining modular lab equipments "environment". Do you have in mind housing? I think that enclosure has to be added in the picture very early.
void_error:
I actually do have housing in mind. I've been following your lab power supply thread and I'm probably going to use one found on modushop.biz, Economica series, 80mm tall. Shipping to Romania is quite expensive though so if anyone knows about any other places in Europe where I can find similar enclosures please let me know.
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