EEVblog #913 - Mailbag

[EEVblog]

More Mailbag

SPOILERS:
Elektor Magazine
https://www.elektormagazine.com/

Elektor Uno R4:
https://github.com/ElektorLabs/Arduino

4D Systems uLCD Gen4 modules:
http://www.4dsystems.com.au/product/gen4_uLCD_24PT/

Adler 805 1970's Calculator
5 1/4" floppy drive Apple II teardown
SolderDoodle USB Rechargeable soldering iron
https://solarcycle.myshopify.com/

Open Source Gossen Multimeter USB serial interface
http://lemmini.de/IrDA%20USB/IrDA%20USB.html

Sony Vaio VGN-UX280P Pocket computer

Epipahn AVIO 4V USB 3.0 video capture teardown
https://www.epiphan.com/products/avio-4k/

http://www.analog.com/media/en/technical-documentation/data-sheets/ADV7619.pdf

NBN fibre optic modem and UPS teardown
http://www.nbnco.com.au/content/dam/nbnco/documents/nbn-fibre-user-guide.pdf

300baud modem teardown

Tektronix 500 series plugin tab replacements:
http://www.ebay.com/itm/Tektronix-TM500-series-plugin-substitute-latch-pull-release-TABS-or-Knobs-5-/131899732191

[guido]

Elektor is from the Netherlands, not from Germany. But i guess they used German post, in some cases it is much cheaper than Dutch post. They are located in a small village next to my home town and we all are very close to the German border. A five minute drive away.

[SNGLinks]

I miss the old Elektor that used TUP and TUN transistors whenever possible.
I have loads of those.

http://www.sentex.ca/~mec1995/circ/tuptun/tuptun.htm

[0xdeadbeef]

Dave killed my Metrahit adapter at first try 

[WN1X]

Dave killed my Metrahit adapter at first try 

Dave is getting better at it 

[anfang]

So, when will the ?ruler be sold again? 

[nowlan]

Dave, have you fiddled with the sound levels recently? Ive had to crank my television up a lot lately.
Could be I am going deaf? Anyone else noticed?

[Brumby]

Dave, have you fiddled with the sound levels recently? Ive had to crank my television up a lot lately.
Could be I am going deaf? Anyone else noticed?

Can't say I've noticed anything different - but then I do find I have to adjust volume levels on a regular basis because other videos are all over the place.  Settings here seem normal, actually.

[boffin]

Bulletin boards. You just made me nostalgic. Even spent some time working for the company that wrote BBS software.

---
 * SLMR 2.0 - on a clear disk you can seek forever

[rs20]

Dave killed my Metrahit adapter at first try 

Not to be too harsh, but I feel like Dave is going to get the flak here for someone else's mistake again (just like that horrendously poorly packaged silicon wafer a while back). Why the sharp, stress-concentrating corners in the plastic? Why the brittle material? Why the solid block of plastic, rather than gently curving spring-like shapes that offer some flexibility and reduce the requirement for dimensional accuracy? It's not like he was overly rough with it, he just tried plugging it in and it go so stuck that it couldn't reasonably be removed non-destructively.

The electronics and software look wonderful in your device, but I'm sorry to say, Dave did not kill your adapter. It just broke.

[TheSteve]

Dave, have you fiddled with the sound levels recently? Ive had to crank my television up a lot lately.
Could be I am going deaf? Anyone else noticed?

I found the audio level very low as well - at least compared to the advertisement YouTube provided before it.

[0xdeadbeef]

Not to be too harsh, but I feel like Dave is going to get the flak here for someone else's mistake again (just like that horrendously poorly packaged silicon wafer a while back). Why the sharp, stress-concentrating corners in the plastic? Why the brittle material? Why the solid block of plastic, rather than gently curving spring-like shapes that offer some flexibility and reduce the requirement for dimensional accuracy? It's not like he was overly rough with it, he just tried plugging it in and it go so stuck that it couldn't reasonably be removed non-destructively.
The electronics and software look wonderful in your device, but I'm sorry to say, Dave did not kill your adapter. It just broke.

Well, the rectangular vertical edges and the brittleness of the material come naturally with acrylic cut cases. Obviously acrylic cases need a bit of care and easily break when applying raw force.
Also the two slots have a pretty complex three dimensional shape, so coming up with a 3D printed design that fits perfectly would be a major effort.
Of course the acrylic case isn't ideal and more of a stopgap solution but it's cheap and the simplest and most effective way to create small cases like this.
I used several of these adapter with my two Metrahits and I tested Dave's in both before sending it, so it could have survived a little bit longer with more careful handling.
Then again, it was probably optimistic to assume that someone who uses a gigantic Bowie knife for unwrapping would handle my poor little adapter with the same loving care as I do

[Fungus]

Dave, have you fiddled with the sound levels recently? Ive had to crank my television up a lot lately.
Could be I am going deaf? Anyone else noticed?

I found the audio level very low as well - at least compared to the advertisement YouTube provided before it.

I don't think I want Dave compress his audio to compete with Youtube adverts.

[chavotronic]

I am sure Isaac is a lier about beeing the inventor of the solderdoodle thing.
Weller is selling this Soldering Iron for years.

[rs20]

Well, the rectangular vertical edges and the brittleness of the material come naturally with acrylic cut cases.

I'm talking about the fact that you have sharp inner corners, rather than using radii. Inner radii are perfectly amenable to laser cutting, and the failure points on your device seen in the video were clearly at sharp corners. It's perfectly plausible for me to claim that a simple 3mm radius would have prevented this particular breakage. See: http://support.ponoko.com/hc/en-us/articles/220289028-How-to-make-interlocking-acrylic-designs Not to mention that you could have (with the benefit of hindsight, to be fair), used edges in the prongs that bowed slightly outwards and had cuts down the middle to allow a little bit of flexing, to limit the friction forces, make the dimensioning less critical, and prevent the prong from being so incredibly tightly wedged.

You can justify the choice of acrylic all you want, and I agree that that particular choice may make sense, but the particular wall thickness and lack of inner radii were free choices that you made! The only reason I'm being so harsh here is because you used rather accusative language (but I should give you the benefit of the doubt as you're not from an English-speaking country), when in reality there has to be a line where a design is just overly weak rather than the victim of unreasonable force. Look how hard he had to try to get the wedged bit of acrylic out! How could he have done that non-destructively, with the rest of the device in the way!?

[Brumby]

Well, the rectangular vertical edges and the brittleness of the material come naturally with acrylic cut cases.

I'm talking about the fact that you have sharp inner corners, rather than using radii. Inner radii are perfectly amenable to laser cutting, and the failure points on your device seen in the video were clearly at sharp corners. It's perfectly plausible for me to claim that a simple 3mm radius would have prevented this particular breakage.

Indeed.  The mechanical design was lacking.  Stresses occur in every object and when there are changes in shape - such as corners - the stresses are increased in that region.  The sharper the change, the greater the forces are focused.  In the case of a 90º square cut, the corner is going to face extreme force concentration and a crack will start very easily ... and once a brittle material has a crack, it is going to propagate instantly.

Curves are your best friend.  Learn to incorporate them in the design when mechanical loads are expected.

[Zbig]

I am sure Isaac is a lier about beeing the inventor of the solderdoodle thing.
Weller is selling this Soldering Iron for years.

  Man, that was low. What was he thinking?

[Fungus]

.... prevent the prong from being so incredibly tightly wedged.

This was the real problem.

The other problem is that the thing simply isn't the same shape as the weird holes in the meter. If you make it less tight fitting it will probably fall out.

I don't see an easy solution if all you have is a laser cutter and some acrylic.

[0xdeadbeef]

The other problem is that the thing simply isn't the same shape as the weird holes in the meter. If you make it less tight fitting it will probably fall out.
I don't see an easy solution if all you have is a laser cutter and some acrylic.

Exactly. As discussed above, the holes in the meter have a very complex shape and there is obviously no way whatsoever to come up with a much better fit with that kind of acrylic cut case.
Yet, the fit is (well, was) not almost as close as you'd imagine. The trick is to insert it exactly in the middle and wiggle a little until it fits in easily. I guess Dave tilted it and it got stuck.

As a side note, the video shows clearly that it didn't even break at a sharp edge but in the curve stretching around the brass spacer. So it didn't break because of stress introduced by sharp edges
as the weisenheimers speculate but simply because 2.3mm brittle acrylic can't withstand a lot of force.
Heck, this was originally meant as a protection from dust and short circuits but then I added the two prongs to be able to attach the thing to the multimeter without external fixture.
Anyway, by screwing the layers together, the case is much stronger than the single layers are. Actually the two cases I have lying around here feel very strong.
Well, I would have never imagined someone could break it without intention, but probably I was underestimating the Aussie brute.

[Zbig]

Well, I would have never imagined someone could break it without intention, but probably I was underestimating the Aussie brute.

If you're trying to be funny, it's not working. If you're seriously throwing a tantrum over your gizmo, that's pathetic. Grow a pair, FFS.

[Fungus]

Well, I would have never imagined someone could break it without intention, but probably I was underestimating the Aussie brute.

Well.... he is a fitness instructor who does "Aussie Bloke" things.

Maybe you could make the prongs with all the layers of acrylic instead of just the central one. Put a vertical bolt through each prong to hold it all together.

[0xdeadbeef]

Maybe you could make the prongs with all the layers of acrylic instead of just the central one. Put a vertical bolt through each prong to hold it all together.

Don't wanna be nitpicking but there are two layers with prongs. And it would be pointless to have the (same) prongs in more layers as they wouldn't touch the holes' walls due to their odd shape.
Back then, I thought about using wider prongs in the next layers but this would have looked weird. And well, the PCB would have needed prongs as well and I didn't like that idea.
Anyway, I don't really intend to invest more time into this. I made a few of these cases, they were relatively cheap and they work perfectly fine for me.
There is simply no reason whatsoever for me to invest time and money to make them bullet proof. It's not like I want to sell them or get praised by mechanical engineers.
If someone wants to improve the case, he/she is invited to do so. The DXF file in the bitbucket repository would be a good starting point.

[Cerebus]

Maybe you could make the prongs with all the layers of acrylic instead of just the central one. Put a vertical bolt through each prong to hold it all together.

Don't wanna be nitpicking but there are two layers with prongs. And it would be pointless to have the (same) prongs in more layers as they wouldn't touch the holes' walls due to their odd shape.
Back then, I thought about using wider prongs in the next layers but this would have looked weird. And well, the PCB would have needed prongs as well and I didn't like that idea.
Anyway, I don't really intend to invest more time into this. I made a few of these cases, they were relatively cheap and they work perfectly fine for me.
There is simply no reason whatsoever for me to invest time and money to make them bullet proof. It's not like I want to sell them or get praised by mechanical engineers.
If someone wants to improve the case, he/she is invited to do so. The DXF file in the bitbucket repository would be a good starting point.

A quick and dirty fix might be to make the prongs a loose fit in the hole, then slap some silicone rubber putty around them, push the whole assembly into the meter, tweek and leave to set. Once set, pull out and you have a perfectly fitting set of partly flexible prongs. The acrylic prongs would need some castellations or similar to give a key for the rubber boot to grip.

[Fungus]

Maybe you could make the prongs with all the layers of acrylic instead of just the central one. Put a vertical bolt through each prong to hold it all together.

Don't wanna be nitpicking but there are two layers with prongs. And it would be pointless to have the (same) prongs in more layers as they wouldn't touch the holes' walls due to their odd shape.

Not pointless: They'd be stronger if you join them together.

There is simply no reason whatsoever for me to invest time and money to make them bullet proof. It's not like I want to sell them or get praised by mechanical engineers.

It broke on the first use. 

[0xdeadbeef]

Not pointless: They'd be stronger if you join them together.

The prongs didn't break. If at all it would make more sense to glue the layers instead of just pressing them together with the bracers/screws.

It broke on the first use. 

Dave broke his on first use. Mine (plural) work perfectly fine for several months. So why would I care to improve something that works for me?
Anyway, I'm out of this. You guys may invest unlimited amounts of your time and money into engineering unbreakable stuff that you give away for free, but I won't.