EEVblog #291 – USB Power Supply Part 2 – The Housing - Page 1
Forum section: electronics / general

author: ericmblog
author_rank: Newbie
timestamp: June 12, 2012, 04:01:53 pm
content: It looks like on one case half, the screw posts you would attached the plexi cover to are not recessed. Is that the case?

author: robrenz
author_rank: Super Contributor
timestamp: June 12, 2012, 04:13:09 pm
content: 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.

author: Lightages
author_rank: Unknown
timestamp: June 12, 2012, 04:46:25 pm
content: DaveI 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.

author: PA3BNX
author_rank: Regular Contributor
timestamp: June 12, 2012, 05:47:19 pm
content: Hello Dave,I think your new housing has a deficits that's where the bound plugs comeit is not fully supported every where around andif you plug in some banana stuff that goes heavy it bends ?For the rest it's okay I think

author: G7PSK
author_rank: Super Contributor
timestamp: June 12, 2012, 06:00:05 pm
content: 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.

author: markus_b
author_rank: Regular Contributor
timestamp: June 12, 2012, 06:49:39 pm
content: 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' ?

author: SeanB
author_rank: Super Contributor
timestamp: June 12, 2012, 07:09:38 pm
content: 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.

author: robrenz
author_rank: Super Contributor
timestamp: June 12, 2012, 07:14:48 pm
content: Quote from: SeanB on June 12, 2012, 07:09:38 pmYou 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.

author: FenderBender
author_rank: Super Contributor
timestamp: June 12, 2012, 07:43:21 pm
content: 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.

author: FenderBender
author_rank: Super Contributor
timestamp: June 12, 2012, 07:45:25 pm
content: Quote from: SeanB on June 12, 2012, 07:09:38 pmWhat'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.

author: ericmblog
author_rank: Newbie
timestamp: June 12, 2012, 07:48:57 pm
content: Quote from: FenderBender on June 12, 2012, 07:45:25 pmAgreed, 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.

author: T4P
author_rank: Super Contributor
timestamp: June 12, 2012, 07:55:05 pm
content: 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

author: robrenz
author_rank: Super Contributor
timestamp: June 12, 2012, 08:29:20 pm
content: Quote from: FenderBender on June 12, 2012, 07:45:25 pmNon 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.

author: FenderBender
author_rank: Super Contributor
timestamp: June 12, 2012, 08:30:43 pm
content: 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.

author: robrenz
author_rank: Super Contributor
timestamp: June 12, 2012, 08:51:35 pm
content: Quote from: FenderBender on June 12, 2012, 08:30:43 pmThe 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.

author: markus_b
author_rank: Regular Contributor
timestamp: June 12, 2012, 09:36:02 pm
content: Quote from: SeanB on June 12, 2012, 07:09:38 pmThe 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.

author: FrankT
author_rank: Regular Contributor
timestamp: June 12, 2012, 09:57:11 pm
content: 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.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 12, 2012, 10:55:40 pm
content: Quote from: Lightages on June 12, 2012, 04:46:25 pmI 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.

author: samgab
author_rank: Frequent Contributor
timestamp: June 12, 2012, 10:58:09 pm
content: 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-ReviewYeah, 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.

author: FenderBender
author_rank: Super Contributor
timestamp: June 12, 2012, 11:54:32 pm
content: 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.

author: samgab
author_rank: Frequent Contributor
timestamp: June 13, 2012, 12:09:03 am
content: Yeah, I know. I wasn't seriously suggesting he do a home made case. Unless just for prototyping purposes and one-offs.

author: naimis
author_rank: Contributor
timestamp: June 13, 2012, 12:50:11 am
content: 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.

author: Lightages
author_rank: Unknown
timestamp: June 13, 2012, 01:48:47 am
content: Quote from: naimis on June 13, 2012, 12:50:11 amI 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.

author: FenderBender
author_rank: Super Contributor
timestamp: June 13, 2012, 02:33:01 am
content: Quote from: Lightages on June 13, 2012, 01:48:47 amYes. (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.

author: Zad
author_rank: Super Contributor
timestamp: June 13, 2012, 02:39:33 am
content: 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).

author: FenderBender
author_rank: Super Contributor
timestamp: June 13, 2012, 02:47:03 am
content: Quote from: Zad on June 13, 2012, 02:39:33 amRubber bumpers would be much more professional than stick on rubber feet, I agree.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 13, 2012, 03:16:46 am
content: The link (to the video) on the front page is wrong.

author: EEVblog
author_rank: Unknown
timestamp: June 13, 2012, 08:57:50 am
content: I understand the concern with the housing. However I have yet to find another suitable case that meets the credit card size form factor with removable end and at a comparable price.If you know of aspecific onethat does, please point it out.I expect the PSU to be handheld a lot, and possibly operated while in the hand, rendering the curved bottom moot in those cases.It's a compromise I thought was worthwhile given case availability and price.As usual, people like to throw around all sorts of solutions, but they haven't really looked in to the finer details and costs of it, and that's when you often "come a gutsa".I am actually considering the PCB top like the uCurrent, with components underneath and touch switches, negating the extra cost for the custom plastic. But the devil is in the detail. For example, that instantly doubles the price of the micro. But that might come out in the wash.Dave.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 13, 2012, 09:11:28 am
content: Quote from: EEVblog on June 13, 2012, 08:57:50 amIs that for touch peripherals or just extra pins? For simple PCB touch buttons which have just resist/silk over them you don't really need touch peripherals as you can easily do it with just pins, measuring discharge time over a few uS with ~100K pullup.

author: EEVblog
author_rank: Unknown
timestamp: June 13, 2012, 09:25:15 am
content: Quote from: mikeselectricstuff on June 13, 2012, 09:11:28 amI've speced in an ATtiny48AU which is $0.86 in 1Kqty. There seems to be a significant jump up in price when going to even moderately more feature rich micros.Could probably do as you say, but I've never tried it that way. Would require some testing I suspect.Dave.

author: pickle9000
author_rank: Super Contributor
timestamp: June 13, 2012, 09:40:28 am
content: Personally I'd like to see the plastic much stronger and safer. Yes it may get a scratch or two but it is a tool. If your worried about it get a sock to carry it. It's not a real tool without some burns and scratches on it.If you have the space for a couple more buttons I'd love to see a couple of one touch presets and perhaps a simple keyboard lock. The actual size looks very good and while knobs are nice on a bench unit, they could cause damage on a small rig like this.I'm really curious to see how the display was going to be set up....mike

author: EEVblog
author_rank: Unknown
timestamp: June 13, 2012, 09:57:24 am
content: Quote from: pickle9000 on June 13, 2012, 09:40:28 amYes, scratches are inevitable I guess. And if it was a PCB front panel, it would just get scratched as well I suspect. Would definitely need the tougher photo-imageable component overlay like CircuitLabs (NZ) do in this case.QuoteNo room, sorry.QuoteYou'll see!I'm still not sure how good it's going to be, but it's very cheap.Dave.

author: markus_b
author_rank: Regular Contributor
timestamp: June 13, 2012, 10:00:49 am
content: What about the same box as the uCurrent ?You could mount the output poles on the sidewall. All the other components go on the PCB.Yes, the resulting device is thicker than you would like, but it will have the 'EEVblog-look' (tm). Also, when I carry a power supply then I'll carry allkinds of other junk as well, so I'll take a big laptop bag.

author: G7PSK
author_rank: Super Contributor
timestamp: June 13, 2012, 11:17:39 am
content: How about polycarbonate instead of perspex it can be thinner and is scratch resistant.

author: EEVblog
author_rank: Unknown
timestamp: June 13, 2012, 01:19:15 pm
content: Quote from: G7PSK on June 13, 2012, 11:17:39 amI'm pricing both out now.Dave.

author: robrenz
author_rank: Super Contributor
timestamp: June 13, 2012, 01:35:24 pm
content: Quote from: EEVblog on June 13, 2012, 01:19:15 pmBoth are available with SAR (super abrasion resistant) coating that is not much more expensive.

author: TopGunPk
author_rank: Contributor
timestamp: June 13, 2012, 02:34:48 pm
content: Hi Dave.Good housing design, specially when you can use 1 case to make 2 (Top and bottom cover).One thing though - since this is a USB powered PSU, do not you think the 7-segment LED displays will chew up a lot of current from the USB bus ? Considering minimum and maximum current draw, assuming you are not doing any fancy multiplexing on the display segments.If the display shows "1", it means only 2x LEDs are lit up, while worst case scenario could be all displays showing "8888". That would not leave much room for the DC-DC converter. Or am i missing something here ?Regards,Zeeshan

author: markus_b
author_rank: Regular Contributor
timestamp: June 13, 2012, 03:53:28 pm
content: Was browsing for boxes, here an alternatives:Hammond 1551 Series (around $2 a piece):http://www.hammondmfg.com/dwg9.htm

author: pickle9000
author_rank: Super Contributor
timestamp: June 13, 2012, 06:50:33 pm
content: Quote from: EEVblog on June 13, 2012, 09:57:24 am

author: Zad
author_rank: Super Contributor
timestamp: June 13, 2012, 09:04:31 pm
content: Some of the Hammond 1593 series have nearly symmetrical halves (again, one half has countersunk holes) but, crucially, the halves are flat.http://www.hammondmfg.com/1593grp.jpghttp://www.hammondmfg.com/1593ptbl.htmSome have battery doors too. It might be possible to design it so that a talented hacker could swap enclosures and install 4xAA cells, and run it off those.

author: LaurenceW
author_rank: Frequent Contributor
timestamp: June 13, 2012, 09:42:51 pm
content: I think Dave's video raises a couple of really important points, for anyone who is considering making a low-volume product (maybe a few hundred or less). Any custom case (especially any custom mouldings) could easily end up costing you more than the elctronics! You want something cheap, and yet it doesn't want it looking like something a seven-year-old threw together, and that is this.Start with the case first, then figure out how to get your electronics in to it!The second point, which he only briefly alludes to, is designing your front of back panel at the same time as your PCB. Choose a sensible colour (like a black solder mask with white screen printing and viola - a professional looking part, for pennies.I used exactly these two tricks for a bunch of miniature nixie clocks that I have designed. The result (I think), is quite pleasing and professional.

author: 8086
author_rank: Super Contributor
timestamp: June 13, 2012, 09:50:55 pm
content: Quote from: LaurenceW on June 13, 2012, 09:42:51 pmThat is really nice! Where might one find that case? Looks snazzy

author: LaurenceW
author_rank: Frequent Contributor
timestamp: June 13, 2012, 10:34:41 pm
content: 8086, these cases, made by Serpachttp://uk.mouser.com/Search/ProductDetail.aspx?R=A-31-BLACKvirtualkey63500000virtualkey635-A-31-BI actually bought mine from Mouser, but they may be available directly in the UK, now (although the "direct from UK distributor" prices are STUPID! Guess they DON'T want the business...http://www.serpac.co.uk/enclosures/a-series.htm)You can also get moulded clear plastic windows, though optically these are not as good as a piece of acrylic sheet. But then you've got to factor in the cost of someone cutting the acrylic sheet to a non-rectangular profile, of course.

author: Jope
author_rank: Regular Contributor
timestamp: June 14, 2012, 11:34:50 am
content: One (or the) manufacturer of this cases is the Taiwanese company Gainta Industries:Gainta websiteThe case Dave wants to use is one of the 400 series.

author: typeglob
author_rank: Contributor
timestamp: June 14, 2012, 07:30:21 pm
content: I wonder if Dave's going to replace the 7-segment displays with SMD LEDs mounted in a similar pattern. I assume its going to be (partly) machine assembled anyway.Doing away with the housing for the LED displays might require lowering the brightness of the LEDs (so as not to blind people, as you'll be losing the diffusor) and maybe mounting two LEDs per segment.

author: Short Circuit
author_rank: Frequent Contributor
timestamp: June 14, 2012, 07:55:11 pm
content: When a countersunk screw is installed in the bottom hole, you get a flat surface.Decent quality bumperstops actually adhere very well to such surface and won't come off.Also, the screw is sightly recessed, which only improves durability of the feet since they have nowehere to go horizontally.Simple solution for the top half is to duplicate the holes with a countersink drill on bench drill with adjustable stop.

author: Zad
author_rank: Super Contributor
timestamp: June 14, 2012, 08:01:45 pm
content: Using the LCD from the battery powered PSU project would save on inventory and improve the BOM scalability.

author: hlavac
author_rank: Frequent Contributor
timestamp: June 14, 2012, 08:17:13 pm
content: I did a little more precise estimation on what could be possible with the USB power supply as a little competition to Dave's designIt goes the comlpex and expensive routeThis is what I got so far:My imaginary design has two isolated voltage outputs, one fixed 5V and one variable 0-20V with total combined output power of roughly 1.3W, and an isolated logic level RS-232. I may even provide some GPIO to allow for creation of i.e. a simple GAL programmer.Both DC-DC converters are powered from the USB side to avoid double conversion loss.I have put ATmega32U4 on the USB side to handle 2 3digit 7segment LED displays (found nice low current ones which take only 2mA@2.1V per segment) and some controls (not decided yet, buttons for now, probably will attempt two capacitive sliders but I/O is getting scarce on the USB side).It does have capability to do a proper USB handshake and thus negotiate power consumption, has USB remote control interface for the supply and provides virtual serial port that goes to the isolated side as isolated 5V TTL level RS-252.There is an isolated serial bus between the two microcontrollers that 1) controls the PWM that sets voltage and current levels on the isolated side, 2) provides for data path of the measured voltage/curent back to the ATmega32U4 for display on the LED displays and communication over USB to the optional control panel application, 3) allows configuration of the baud rate on the isolated serial bus to the device and 4) passes serial data from the virtual serial port to second UART of the ATmega164A on the isolated side.ATmega164A on the isolated side is doing current and voltage measurements with the internal ADC and sends data back and forth over the middle bus (which runs faster than the virtual serial to allow for internal communication in addition to the user data).I have two 78S40 on the USB side to do the power conversion, voltage is measured on the isolated side with comparators and result is passed back thru two optocouplers (on=too high). Variable voltage is compared against PWM generated threshold voltage generated by the isolated side MCU. This part is too simple and imprecise for now, need to find a way to generate PWM based on a reference not just output of the MCU which depends on its supply fluctuations. Maybe I will just power whole MCU from a voltage reference of some sort.What I'm currently missing is a current limiter on the 5V output. It will be necessary so I dont starve out the isolated side MCU by excessive current.Also I need to figure out how to combine the current limitation of the two converters together into a common power budget without limiting them both to a fixed current value. I'll probably just stick a current limiter between the USB power and the rest of the circuit for some loss in available power.I'm also thinking of a 5V wall adapter connector to allow standalone operation without USB and with more power.So, what do you think, overcomplicated?

author: Bored@Work
author_rank: Super Contributor
timestamp: June 14, 2012, 09:32:49 pm
content: Quote from: hlavac on June 14, 2012, 08:17:13 pmThe 78S40 really hurts. It is a 40 year old switching regulator, basically a MC34063 with an additional opamp. If you plan to go the expensive route, then use modern switching regulators, not that old stuff. It is hard to make an adjustable SMPS, especially, if the input voltage (5V) is within the output voltage range (0 - 20V), and an 78S40/MC34063 makes it even harder.To get an idea what it takes to make an adjustable SMPS, see mike's recent teardown video. And pay attention to the part where he talks about the weird behavior of that SMPS under special loads. That's the SMPS oscillating, because the control loop is not properly compensated for that particular load. And that happens with an SMPS specifically designed to be adjustable. It is not just some bare minimum circuit taken from an app note with the feedback resistors replaced by some PWM interface.As for the rest, two micro controllers communicating over an isolated serial link is a standard technique that was even used before there were micro controllers, but only micro processors. I would not use TTL-level RS232 for it, but SPI (or I2C). The USB side being the master, and the isolated MCU being the slave. And I would only have one isolated bus between the MCUs. The isolated slave doing the actual PWM, while the master just communicates the desired values to the isolated slave over the bus when there is a change. And the master regularly polls the isolated slave regarding the current values (voltage, current), to display it.Once you have the isolated SPI bus (or I2C), you can add more slaves to the isolated side of the bus. E.g. instead of using PWM, you could add some DACs to the bus on the isolated side for voltage and current adjustments instead.I would use a supply voltage of 3.3 V or 3.6 V on the isolated side, not 5V. Generating a stable 5V from the USB voltage is more effort, because the 5V aren't guaranteed. The USB standard says something like 4.5V to 5.5V (you would have to check, I am currently to lazy to look it up in the standard). Using 3.x V means you can just use a modern buck converter.And because of that supply voltage I would drop the fixed 5V output. Either make that 3.x V, or skip the feature.

author: hlavac
author_rank: Frequent Contributor
timestamp: June 14, 2012, 10:20:34 pm
content: Quote from: Bored@Work on June 14, 2012, 09:32:49 pmYeah, but It's all I can get here for cheap. I really need to try Farnell or something. 40 years behind is literally where local component stores are here in Czech RepublicI liked it because it was kind of a set of stuff you need for SMPS, not a magic black box. And unlike the MC34063 the voltage reference is not hardwired to the comparator but connected to a pin.What is wrong with it, except for being archaic? Bad switches? Low efficiency? I would be pretty contempt with about 80%.Quote from: Bored@Work on June 14, 2012, 09:32:49 pmWell the point of RS-232 was it only needs one line/optocoupler per direction. Optocouplers are amongst the more power hungry components in the design, and I'm trying to shave milliwatts here.I got traffic in both ways as the RS-232 port is bidirectional and I can set the voltage in one direction and read the measurement in other. Rest is really as you describe.Quote from: Bored@Work on June 14, 2012, 09:32:49 pmI could just hook that up to the isolated MCU no?Quote from: Bored@Work on June 14, 2012, 09:32:49 pmAs the topology will be flyback thru a 1:1 transformer not buck because of the isolation, that should not be a problem?Or how can you do isolated buck? I don't think you can.I wanted 5V so that I can use it on the external RS-232. Most of my designs are still 5V. Maybe even switch the isolated MCU power rail between 5V and 3.3V depending on what I need for the RS-232.Quote from: Bored@Work on June 14, 2012, 09:32:49 pmI'll think about it. It does seem to complicate things (like I can not use low side current shunt on GND for example as it is shared with the 5V). I'll see if I can figure out the high side current measurement, if not I'll have to drop the 5V.But I'd really like to keep the isolated RS-232 to the powered device...

author: darrenb
author_rank: Contributor
timestamp: June 15, 2012, 03:06:22 am
content: QuoteHi Dave,Remember the logic analyser that you pulled out of the mailbag recently and you though it had a great case? It was just an aluminium extrusion with some customisation done to the end panels.I'm working on some at the moment and a picture of them is below. On the left is a single prototype of a customised extrusion. There are 250 more of them currently being manufactured and hopefully they will be here next week. In the middle is an unmodified sample of another extrusion type which I will have customised. On the right is a commercial battery charger which was the inspiration for my cases and which would probably be fantastic for yours as well.The fully customised product on the left will cost $5.04 each (plus a bit more for shipping by the time they land in Castle Hill) which is a bit more than than the $2 that you're intending to spend. But keep in mind that this is not just a bare case, it also includes solutions for all of the mounting problems you might have, as well as screen printing to finish off the appearance of the unit.

author: EEVblog
author_rank: Unknown
timestamp: June 15, 2012, 04:17:57 am
content: Quote from: Zad on June 14, 2012, 08:01:45 pmAnd cost about 15-20 times more.I would have to change the bench display solution to suit the USB requirements.Dave.

author: EEVblog
author_rank: Unknown
timestamp: June 15, 2012, 04:21:14 am
content: Quote from: darrenb on June 15, 2012, 03:06:22 amI have the same Tunigy charger.Where did you get them customised from and what brand/model?That's very cheap for low run extruded alloy case.Dave.

author: Zad
author_rank: Super Contributor
timestamp: June 15, 2012, 04:22:23 am
content: Crikey, I didn't realise I2C LCDs cost so much more than 7-segment LEDs!

author: EEVblog
author_rank: Unknown
timestamp: June 15, 2012, 04:26:39 am
content: Quote from: TopGunPk on June 13, 2012, 02:34:48 pmYou aren't missing anything. That is why I said I am dropping the 7segment LED displays.Dave.

author: EEVblog
author_rank: Unknown
timestamp: June 15, 2012, 04:30:23 am
content: Quote from: LaurenceW on June 13, 2012, 09:42:51 pmThat looks very nice, and yes, I should have actually been clearer on those points, that is exactly what I was implying.Although for any volume machine assembled run you don't want to combine them like this, as it chews up your usable circuit panel space. So you won't save cost you'll likely increase it. It's the bomb for prototypes though.Dave.

author: Unknown
author_rank: Unknown
timestamp: June 15, 2012, 04:45:46 am
content: Quote from: EEVblog on June 15, 2012, 04:21:14 amA lot of us would be more than interested at those kind of dollars for <1000 batches . Me included!

author: darrenb
author_rank: Contributor
timestamp: June 15, 2012, 07:39:44 am
content: I've PM'd Dave and Vernon with the the name of the factory.I don't think this factory is unique however and there are plenty of manufacturers out there. To find them go to alibaba.com and search for "Aluminium Extrusion Enclosure".You'll then need to spend heaps of time learning how to deal with these factories. Dealing with their MOQ's and learning what FOB or Ex-works means. But it's worth it.For example I need to have 4 tactile switches in each unit I'm making. At Jaycar they are about 90 cents each and the cheapest I can find them at Digikey is about 30 cents each which doesn't sound like a lot, but when you multiply by four and then add four button caps as well it's adding dollars to the project.From a factory in China I can buy them for 1.6 cents each and can therefore buy 1000 of them for $16. At this price I can put them on my cereal.

author: EEVblog
author_rank: Unknown
timestamp: June 15, 2012, 08:41:01 am
content: How much freight would you pay to get like a 500 MOQ delivered to Oz?Dave.

author: darrenb
author_rank: Contributor
timestamp: June 15, 2012, 08:58:55 am
content: Hi Dave,The MOQ is somewhat negotiable. The minimum order quantity on these was 500 but they were able, after a fair bit of negotiation, to supply 250.Shipping quoted by them for these 250 pcs is USD450 for approx 43kg. This is for a 2-3 day express courier like DHL to Castle Hill NSW. I'd like to find a cheaper shipping option but it's something I'm yet to solve.

author: ModernRonin
author_rank: Contributor
timestamp: June 15, 2012, 09:17:09 am
content: I like the idea of a clear top, but how about this... Make the clear top be the sides too!Basically, make it too long left-right, then have the extra length bent downward so you end up with an upside down U-shaped thing. This will give your binding posts something to screw in to.Keeps the BOM count low, looks more professional, theoretically a little stronger than a top and two end panels.Only question is, how much does it cost to get perspex/polycarbonate bent like this?

author: T4P
author_rank: Super Contributor
timestamp: June 15, 2012, 09:42:49 am
content: Quote from: hlavac on June 14, 2012, 08:17:13 pmHandshake? I wouldn't bother with that one. Every computer i have ( Old thinkpads and new llano laptop ) doesn't need negotiation

author: Bored@Work
author_rank: Super Contributor
timestamp: June 15, 2012, 10:46:58 am
content: Quote from: DaveXRQ on June 15, 2012, 09:42:49 amHow should I explain that to you? The sample of computers you have is insignificant.

author: T4P
author_rank: Super Contributor
timestamp: June 15, 2012, 12:02:06 pm
content: Quote from: Bored@Work on June 15, 2012, 10:46:58 amThinkpads from the IBM eraThinkpads from the now-Lenovo eraHP tx2028AUAn acer 5560GAcer cheapie from 2008Fujitsu LH520Insignificant ? I don't think so

author: hlavac
author_rank: Frequent Contributor
timestamp: June 15, 2012, 12:04:34 pm
content: USB port on my Mac keyboard has limited power

author: Christopher
author_rank: Frequent Contributor
timestamp: June 15, 2012, 12:25:35 pm
content: Hi Dave, I have access to a laser cutter and a pile of 3mm Acrylic/MDF if you want some prototypes cutting out. Im in the UK so shipping could take a while.Brill project, make sure you include a DC jack, I'll probably use this as my main PS.

author: proxime
author_rank: Newbie
timestamp: June 15, 2012, 09:31:25 pm
content: How mutch power will the usb power supply be?Is it possible to make it usb 3.0 (current=900mA) or even more with a Y-cable? (http://www.cavalrystorage.com/cbusb20002.aspx) or even better more and more usb ports support battery charging (1,5A)

author: TopGunPk
author_rank: Contributor
timestamp: June 16, 2012, 01:30:18 am
content: Quote from: EEVblog on June 15, 2012, 04:26:39 amPerhaps you can consider 7-segment display LCD screens, much like you have in DMMs. Ok, they may or may not have a back-light AND probably they would require a lot of I/Os or some driver chip(s), BUT they are very low on power consumption and quite DMM like.I am designing around such a display in one of my projects - its a Petrol / Diesel (gasoline for the US people) dispenser system. And one of the Key requirements of the client was that the dispenser should continue to display the last result / current result of the counter when the power failed. The LCD keeps displaying the last amount and Litres dispensed even though the system is OFF, with just a AA cell and draws to the tune of uA (without back-light).

author: hlavac
author_rank: Frequent Contributor
timestamp: June 16, 2012, 01:50:10 am
content: There are nice low current LED displays like Avago HDSP-A101 that need only about 1mA per segment, no need to drop the display!

author: Short Circuit
author_rank: Frequent Contributor
timestamp: June 16, 2012, 08:10:44 pm
content: 36mA is quite significant if you only have 500mA to play with...(2 x 3digit x 6segments on x 1mA

author: Christopher
author_rank: Frequent Contributor
timestamp: June 16, 2012, 11:12:51 pm
content: Quote from: Short Circuit on June 16, 2012, 08:10:44 pmDo you mean 7 segments. Also what about a decimal point?(Sorry for sounding like a tool but im a bit drunk right now)Actually not all 7 segments will be lit.. What do you do regarging resisors when only say 2segments are lit compared to all 7, surely 2 will be brighter than 7?

author: hlavac
author_rank: Frequent Contributor
timestamp: June 16, 2012, 11:46:48 pm
content: No you don't do that you multiplex one digit at a time and cycle thru the 6 of them ~60 times per second, that is only 8 segments on max at once or 8mA, thats not so bad - 0.04WYou can do as low as 0.016W with a 2V power rail if you can take the extra cost of one more DC/DC converter. Probably not worth it for the 1mA displays (would be with 20mA segments).

author: hlavac
author_rank: Frequent Contributor
timestamp: June 17, 2012, 12:03:33 am
content: Quote from: Christopher on June 16, 2012, 11:12:51 pmNo, each segment has its own current limiting resistor so the segment brightness is aways the same no matter how many other segments are on.For common anode displays it goes: power rail -> digit switch transistor (PNP) -> display anode -> segment bus (8x) -> current limiting resistor(8x) -> I/O pin for the segment (8x)Digits are switcghed on with another I/O pin per digit. You output LOW on pins for segments you want to light up, then turn on the digit with its pin (low on I/O pin ->resistor->base of the switching PNP transistor). Let it shine for a while, then turn off, activate next segments and turn next digit and so on.For low power LEDs like the 1mA ones where one I/O pin can take current from all the 8 segments you can skip the transistor and just connect the display anode to the digit I/O pin directly and turn digits on with HIGH.

author: ttp
author_rank: Regular Contributor
timestamp: June 17, 2012, 11:59:33 pm
content: Hi DaveCould you please fix the download link and QuickTime button, both point to VCR teardown episode. Thanks!

author: EEVblog
author_rank: Unknown
timestamp: June 18, 2012, 01:10:50 am
content: Quote from: ttp on June 17, 2012, 11:59:33 pmFixed.Weird, I think Wordpress is screwing up somehow...Dave.

author: EEVblog
author_rank: Unknown
timestamp: June 21, 2012, 03:39:32 am
content: Quote from: Zad on June 13, 2012, 09:04:31 pmAlmost perfect. But unfortunately not high enough, only 11mm pillar which is likely not adequate for the binding post.Dave.

author: neal.sprouse
author_rank: Newbie
timestamp: June 27, 2012, 03:21:45 am
content: Possible custom case.http://www.clickfoldplastics.com/I know there is a setup fee, not sure of pricing. Might give you a break if you show them you site.

author: george graves
author_rank: Super Contributor
timestamp: June 27, 2012, 08:17:17 am
content: Sounds like Dave needs a laser cutter. Here's a great example of what's posiable: