EEVblog #291 – USB Power Supply Part 2 – The Housing

[ericmblog]

It looks like on one case half, the screw posts you would attached the plexi cover to are not recessed. Is that the case?

[robrenz]

You could drill out the holes that the case screws thread into, to the same size as the clearance holes on the other half.  That would let you use the same size screws on both halves to hold the perspex on.  I would get a true plastic screw with the high/low threads to minimize the  stress in the boss because it is probably thinner wall than would normaly be designed for a threaded fastener.

[Lightages]

Dave

I had another idea for the panel instead of Perspex. Why not use a double circuit board design, one lower one and one upper one with the upper one also being the cover? This way you can get everything done at one fab, not need special handling for the extra plastic. You can have the lower board hold the display and buttons with the cutouts in the upper board for them to be visible/accessible. You get more circuit area to work with too. The lower board need not be the full size, just sufficient to hold the display and buttons for example. If you need heat dissipation then the copper in the upper board will also double as a makeshift heat sink.

This way you can carry on your design theme started with the Micro Current, and remove another stage of manufacture and supplier issues.

Additional: Of course the upper board does not need to have circuitry, it could just be a cover if you want to avoid interconnects between the two boards.

[PA3BNX]

Hello Dave,


I think your new housing has a deficits that's where the bound plugs come
it is not fully supported every where around and
if you plug in some banana stuff that goes heavy it bends ?

For the rest it's okay I think

[G7PSK]

Hi Dave, I see you are planning to get the perspex cover laser cut, have you thought about water jet cutting, it will give a much better quality finish and polished edge compared to a laser cut and should not cost any more or be even cheaper as there is no dross at all to be removed.

[markus_b]

I like your approach - innovative and pragmatic.

But I'm not fond of the specific outcome: Your chosen housing is not flat on its sides, so the resulting device will always wobble around on the desk. I find this a real pain. Are there no other boxes around, of similar size, without this 'feature' ?

[SeanB]

4 stickon rubber feet will cure that, and make it non skid as well as a bonus. They will also cover the holes on half the units.

[robrenz]

4 stickon rubber feet will cure that, and make it non skid as well as a bonus. They will also cover the holes on half the units.

You beat me to the punch.  These Hammond Manufacturing 1421T6CL would be perfect .31" dia. x .09" high hemispherical shape.  I have used these a lot, they stick very well on degreased surfaces. Data sheet attached.

[FenderBender]

I think the case would be okay to "slip into a bag" as you say....but I'm shocked that you have not realized that the bottom of your enclosure is NOT FLAT. Remember all of those multimeter review videos where you always bashed the meters for sliding around and wobbling? That's exactly what these enclosure is going to do to your project. Maybe you have a solution, but I definitely would like to see a case with flat sides. Beveled enclosures are nice if the device is going to be handheld, but if it's a test instrument (power supply), then you'd most likely have it on a bench somewhere.

My opinion, but please consider it. I don't want the project to be ruined because of a stupid thing like this.

[FenderBender]

4 stickon rubber feet will cure that, and make it non skid as well as a bonus. They will also cover the holes on half the units.

What's the point of rubber feet if you can just use a flat case? If you have rubber feet, what even the advantage of this rounded case? No?

Now try sliding an enclosure with rubber feet into a case? I don't know. Seems tacky to me.

I understand covering the holes, I just don't understand why you would use an enclosure that needs to be "fixed" while you could probably find one that is fine right off the bat. Could be wrong, and I've done little research, but that's my 2cents.

[ericmblog]

What's the point of rubber feet if you can just use a flat case? If you have rubber feet, what even the advantage of this rounded case? No?

Now try sliding an enclosure with rubber feet into a case? I don't know. Seems tacky to me.

I understand covering the holes, I just don't understand why you would use an enclosure that needs to be "fixed" while you could probably find one that is fine right off the bat. Could be wrong, and I've done little research, but that's my 2cents.

Agreed, I would rather have a wobbly case than rubber feet. If you are going to include them, just put them in the package, don't stick them on.

[T4P]

A flat case... er... well clearly without rubber feet *applies DJ's lack of love for slidy meters*
A wobbly case is alright. Remember, if the displays and the buttons end up flush, you can put the PSU flat on a table if you please

[robrenz]

What's the point of rubber feet if you can just use a flat case?

Non skid use and a little compliance for surfaces that are not perfectly flat.  The feet I posted here are almost invisible. they are only 2.8mm high and 8mm dia.

[FenderBender]

What do you mean compliance for a surface not perfectly flat? I think a flat case is still going to have more surface area on the ground that a rounded one.

[robrenz]

What do you mean compliance for a surface not perfectly flat? I think a flat case is still going to have more surface area on the ground that a rounded one.

The case curvature is large enough that only the feet are going to touch the surface you place the case on.  These feet are hemispherical they touch on a theoretical point contact.  since they are rubber/urethane they deform rather easily if it is a small contacta area. When the feet contact a surface they will give a little to conform initially until the contact patch starts to widen.  I am talking small amounts here like several mils. With an instrument like this with pushbutton operation the  solid solid stable feel the feet will give is a plus.

[markus_b]

4 stickon rubber feet will cure that, and make it non skid as well as a bonus. They will also cover the holes on half the units.

The problem with rubber feet, glued on, is that they will not stay on for very long. If the unit is in my laptop bag, then the rubber feet will have a half-life of weeks. Sooner or later they will stick to everything in the bag, but the power supply.

[FrankT]

What's the next step?  Are you going to make a 3D CAD model to make sure it will all fit, or are you going straight to a prototype?

Those binding posts look like a tight fit, especially the nuts that hold them.

[mikeselectricstuff]

Dave

I had another idea for the panel instead of Perspex. Why not use a double circuit board design, one lower one and one upper one with the upper one also being the cover? This way you can get everything done at one fab, not need special handling for the extra plastic. You can have the lower board hold the display and buttons with the cutouts in the upper board for them to be visible/accessible. You get more circuit area to work with too. The lower board need not be the full size, just sufficient to hold the display and buttons for example. If you need heat dissipation then the copper in the upper board will also double as a makeshift heat sink.

This way you can carry on your design theme started with the Micro Current, and remove another stage of manufacture and supplier issues.

Additional: Of course the upper board does not need to have circuitry, it could just be a cover if you want to avoid interconnects between the two boards.

I think this may have some advantages - you could stick a thin plastic window on the underside for the display.
An issue with an acrylic cover is it will get scuffed and scratched, but a rear-mounted  window will be recessed and better protected.
PCB top also allows more room for text etc. You could maybe also incorporate touch buttons or sliders.

[samgab]

Wanna do something REALLY awesome (and annoying and time consuming to produce), Dave?
How about printing your own cases to your own spec. using your 3D Printer? That would be so cool.
I see that's what the Cottonpickers guy is doing with his new model USB Li-ion charger.
http://www.candlepowerforums.com/vb/showthread.php?336422-Cottonpickers-Nona-Charger-Review
Yeah, I was so impressed by that I've started a new thread just about those Cottonpickers chargers. I think they're cool, and the self-3D-printed case on the new ones just adds extra cool-factor.
The one in the review above is just a sample prototype version, so it's been printed at half the 3D print resolution he's going to use for the proper versions, apparently.

[FenderBender]

But if he intends to sell them, that's going to be a pain in the arse. I don't know how much the plastic for makerbot costs, but somethow I imagine it's going to look more professional with a proper case and without all those ugly beads. Fine for a one time thing. Not sure about medium scale production.

[samgab]

Yeah, I know. I wasn't seriously suggesting he do a home made case. Unless just for prototyping purposes and one-offs.

[naimis]

My thought was that instead of burying the PCB internally and using perspex for the bottom, make it like the uCurrent where the PCB is the top of the housing.  Low-profile LCD display and capacitive touch inputs for the interface.  I'm sure there are any number of reasons to dislike this approach, not the least of which is having either ugly through hole wires sticking through or having to do everything using SMT, but it's my idea and I like it.

I'm too lazy to actually go out and design and build such a thing, though.

[Lightages]

My thought was that instead of burying the PCB internally and using perspex for the bottom, make it like the uCurrent where the PCB is the top of the housing.  Low-profile LCD display and capacitive touch inputs for the interface.  I'm sure there are any number of reasons to dislike this approach

I think that when Dave was thinking "throw it in the computer bag" he was worried about the surface mount components on the top being knocked off or broken. This thing needs a robust construction.

[FenderBender]

My thought was that instead of burying the PCB internally and using perspex for the bottom, make it like the uCurrent where the PCB is the top of the housing.  Low-profile LCD display and capacitive touch inputs for the interface.  I'm sure there are any number of reasons to dislike this approach

I think that when Dave was thinking "throw it in the computer bag" he was worried about the surface mount components on the top being knocked off or broken. This thing needs a robust construction.

Yes. (This is not directed at you) But how exactly is a glue on/stick on rubber foot supposed to be robust? It's not. I know the case isn't that round and it wouldn't be too much of an issue if knobs were going to be used, but tactile switches are pains in the arses with a flat surface, nevermind a wobbly one. Unless you have something else in mind, Dave. I think it would just be so much better if it had a solid foundation.

[Zad]

As you say, a wobbly back to an enclosure is a total non-starter when using tactile switches. Maybe this would be a good excuse for Dave to investigate the ins and outs of injection moulding manufacture? Even if it is just rubber "bumpers" that he can fit over each end of the enclosure (although the asymmetric lip on each half is kinda clunky too).