EEVblog #643 - Mailbag

[EEVblog]

[Simon123]

Did u used 3V on meter to power it on or 1.5V.
2R10 is 3V battery.

[Mark Hennessy]

I bought my fx7000G in 1989 for my A-levels, and still use it daily. I have tried many newer Casio calculators, but keep going back to the 7000. I guess that after 25 years, I'm used to it. Recognising that it's getting old, I bought a couple second-hand, and they are in pretty mint condition. Good job I did, as no-doubt the prices will shoot up now

[kcs]

I am very curious how did he got solder mask between those pins. I have used IC in the same package recently and I was not able to get solder mask because of the small pitch. I have used the same PCB manufacturing service as that guy.

Datasheet for IC recommends:
 - Distance between pads - 8 mils
 - Pad width - 17,5 mils

PCB manufacturer's rules:
 - Min solder mask expansion - 3 mils

So we are left only with 2 mils for solder mask.

[nathanpc]

I like the new format, it looks a lot better since the camera isn't too close to the box you're trying to open and you have more room to show the contents before changing to the usual angle.

[rob77]

the new format is great ! 

[Dr. Frank]

Hi Dave,

The new location and perspective (angle) of your videos is really very nice.

The background now is very pleasant (not so uneasy any more, as in the foregoing video), as you cleaned up the racks neatly.

On Long Shots, the picture pane should be a little bit bigger (more wide angled), as your head is cut off periodically. That's quite distracting, during watching your video.

The sound is quite ok, but could be better. I think it sounds a bit hollow now, maybe you had more trebly (?) sound in other videos.

Frank

[Laertes]

I am very curious how did he got solder mask between those pins. I have used IC in the same package recently and I was not able to get solder mask because of the small pitch. I have used the same PCB manufacturing service as that guy.

Datasheet for IC recommends:
 - Distance between pads - 8 mils
 - Pad width - 17,5 mils

PCB manufacturer's rules:
 - Min solder mask expansion - 3 mils

So we are left only with 2 mils for solder mask.

These boards were made by OSHPark, apparently. They don't really specify minimum soldermask width but I'd venture a guess it's going to be 4mils. Make the soldermask expansion only 2 mils and there you go.
In my experience, soldermask expansion specs are pretty loose by the manufacturers, with OSHPark or my local source here, I've never run into an issue with 2 mils or occasionally just 1 mil. My local manufacturer actually recommends going for 4mils.

[Laertes]

Oh and I forgot: The new format is great! 

[kcs]

Laertes, yes, I know it is OSH Park. And yes, they do specify min solder mask expansion, just load DRC file they provide.
My points was, if I follow the DRC rules, I cannot put solder mask between those pins. Of course I can choose not to follow them and accept the risk.

[Alexei.Polkhanov]

Those MOSFETs are impressive but 0.19 ohm RDS On won't put them into "world best in TO220 package" category. I recently ordered
IRFB41110 ($6 on Digikey) - RDS ON is 3.7 mOhm - that is milliohm. http://www.irf.com/product-info/datasheets/data/irfb4110pbf.pdf

[rob77]

Those MOSFETs are impressive but 0.19 ohm RDS On won't put them into "world best in TO220 package" category. I recently ordered
IRFB41110 ($6 on Digikey) - RDS ON is 3.7 mOhm - that is milliohm. http://www.irf.com/product-info/datasheets/data/irfb4110pbf.pdf

i bet those 3.7mOhm are not rated for 600V , are they ?

[free_electron]

pff. the lab is too clean  if a cluttered desk is a sign of a cluttered mind, then what is an empty desk a sign off.
a lab is oly a lab if there's oodles of cables running between and to/from instruments and a mystery board.

equipment sitting on a shelf means it is not being used, so basically ballast and occupying valuable space. time to clean out the 'surplus' and give it away  > ( no, i don't want any , unless it's got a HP or Agilent logo on it, and even then if it's got the old clickety pushbuttons i don't want it. )

[Laertes]

Laertes, yes, I know it is OSH Park. And yes, they do specify min solder mask expansion, just load DRC file they provide.
My points was, if I follow the DRC rules, I cannot put solder mask between those pins. Of course I can choose not to follow them and accept the risk.

Sorry, I can't view that due to lack of Eagle(why don't they put all the info on their site... ). So that's expansion, do they specify minimum solder mask width(or sliver, as Altium calls it, or whatever Eagle calls it)
Well anyway, from experience: Yes you can go with 2 mils and I've definitely soldered a few hundred pins with 2 mils on OSHPark boards and I can't recall a single issue with soldermask...

[rob77]

@ free_electron:
i think the stock of equipment on the shelves is an excellent background for the videos. i would definitely keep it as it is

[sonnytiger]

I am almost certain I used to have the thinner version that Dave spoke of, I had it when i was a kit, it was awesome. I wish i still had it, haha.

[German_EE]

    

Three thumbs up for the new video format. I presume it's just camera angles that's stopping you from doing mailbag teardowns the same way?

[max666]

That universal dimmer is interesting, I would have expected only a Phase-fired Controller with a triac a diac two caps and a couple of resistors, but that thing is packed with components. 

[djacobow]

I'd be interesting in learning more, too!

I've built a few AC dimming type devices now, and none were exactly this complex. I've done reverse phase angle devices using just a TRIAC (and I've torn down a few wall box dimmers that work this way) and I've also done the FET-in-a-bridge type. In both cases, I used a opto to do ZC detection and the timing for firing the dimmer was done by a microcontroller. I guess the uC can replace a lot of bits and bobs of analog. It's kind of insane to use a computer to do the job of a few transistors, but for a hobbyist, it's definitely cost effective and the computer enables some really cool features like "soft" on/off.

Anyway FET-in-a-bridge enables forward phase angle dimming (or any shape, really: tails only, peak only, etc) but I'd be curious to know why they needed two FETS. Are they in parallel to reduce Rds?

I wonder if this device actually measures the current waveform and does some adaptive magic to make the dimmer just work "better" with various loads.

That universal dimmer is interesting, I would have expected only a Phase-fired Controller with a triac a diac two caps and a couple of resistors, but that thing is packed with components. 

[superUnknown]

So how is that dimmer actually working with only two mosfets? Those diodes ensure that each fet sees half the waveform and then in turn the uC clips it to suit?

[djacobow]

It can work with just one. You put the FET at the "DC" terminals of a bridge rectifier. The FET always sees voltage the same way. The load is in series with the "AC" terminals of the rectifier. In my experience, driving the FET can be somewhat complicated depending on what you are referencing your driver circuit to.

I can see using two FETs in a not-bridge rectifier, where each handles on half of the cycle. This might be better; I haven't really thought about it.

So how is that dimmer actually working with only two mosfets? Those diodes ensure that each fet sees half the waveform and then in turn the uC clips it to suit?

[max666]

Looking at the bottom board in Daves video, I can not see how those four diodes can form a bridge rectifier, I mean the AC input goes straight to the centre pins of the MOSFETs, which would be drain.

I think each MOSFET handles one half of the cycle, like djacobow suggested.

[smashIt]

dave, the first grapghics calculator was the fx-7000g, not the fx-7000gb

i own a fx-7000ga, so there were quite a few versions of the fx-7000

[FreudianSip]

The B you see in German street names is actually not a B- it's pronounced as a double s sound. StraBe is pronounced "strasse"!

[david77]

That Ohmmeter is called a "Leitungsprüfer" which literally means line tester. These crude devices were commonly used by telecomms people to check their POTS wiring, relais and strowger switches back in the day. A bit more sophisticated than a bulb and battery but not in any way a precision instrument. West German companies like Gossen, Metrawatt, Siemens also made similar devices but not until 1989 I suspect.

The 2R10 battery was quite common and usually called a flashlight battery in Europe, it contains two 1,5V cells stacked in a paper or plastic shroud, these single cells fit into these meters.

I nabbed a pic off the interwebs:


I'd suspect the case is bakelite or something similar, so I don't think it'd really survive a fall...
These things were mostly obsolete by 1989, at least in the west. It probably had something to do with the unique way East Germany was run that they still made them to the end.

Also quite interesting to note who made that thing: VEB Klingenthaler Harmonikawerke
That was a state owned (VEB means Volkseigener Betrieb - state owned company) maker of musical instruments mainly harmonicas, a bit of PA gear and electronic organs. Again, a sign of a state managed economy.

[MouseBiteFever]

I am very curious how did he got solder mask between those pins. I have used IC in the same package recently and I was not able to get solder mask because of the small pitch. I have used the same PCB manufacturing service as that guy.

Datasheet for IC recommends:
 - Distance between pads - 8 mils
 - Pad width - 17,5 mils

PCB manufacturer's rules:
 - Min solder mask expansion - 3 mils

So we are left only with 2 mils for solder mask.

I don't think I did anything special. I just loaded up the OSHPark DRC and put the board together.
I'm adding a close up pic of the pads and tstop. The spacing is 5mil/div
digikey lists the package as "Package / Case   8-TSSOP (0.173", 4.40mm Width)"
I'm also adding the dimensions from the data sheet

[RupertGo]

The new format is a definite improvement, although Dave now looks a bit like a TV anchorman. Perhaps some portentous music and pointlessly swoopy glittery animation at the front? As for the shelves behind - if a bunch of scopes can be wired up to show key metrics in real time (hits/sec, comments/min, Dave's blood pressure, swear index, etc) then it'll be much more Star Trek and thus much more to my taste.

I do hope someone has the circ for the dimmer, or something like that. In a past life, I was part of a team doing comparative testing of UPSs, which is a seriously hard job and one we really did have to stop working on rather than finish. I learned (well, was exposed to) a ton of stuff on that project, including just how mad mains electricity looks in a large building filled with mid-90s vintage IT running off second-generation SMPSUs. It's a very hard environment to properly appreciate, let alone design for, especially for a chap whose previous PSU knowledge stopped at four diodes, a centre-tapped transformer, a couple of caps and an excuse-me.

Designing a half-kilowatt universal dimmer that isn't going to do something impolite seems to me to be a long-trousered job and a half. Some insight would be much appreciated.

R

[deth502]

gold guilding is fairly easy if you can manage to not mangle the gold.

you coat the edge with an adhesive, then just place the thin, thin THIN, VERY THIN gold sheets over the adhesive and press on. the un glued portions will easily just wipe off since the sheet is so thin.

it is so thin, its even easily eaten. heres some guilding sheets, these happen to say they are designed for food. the same as if you have ever seen/drank goldschlager vodka.

http://www.deandeluca.com/pantry/baking-ingredients/giusto-manetti-23k-gold-leaves.aspx?ref_code=GoogleMerchant&gclid=COOy88302b8CFQwV7AodGX4AIg

a common thing done with large guilded areas (like letters on a sign) is to use a small sponge on a stick to swirl an engine turned finish into the guilding.

[deth502]

a videos worth a thousand words.



and turning

[synapsis]

Quick question:

On the German ohmmeter, the meter face has a line of symbols (looks like Egyptian hieroglyphs ). What do these symbols mean? I've purchased a couple of OneHungLo analog meters off eBay in the past that also had symbols, so I assume they mean *something.*

[Simon123]

It tells you type of moving coil or iron, input protection, accurecy, orientation ...
If i find picture defining it il post ti.
https://www.eevblog.com/forum/testgear/exploring-the-symbols-on-a-analog-multimeter-quiz/

[djacobow]

Designing a half-kilowatt universal dimmer that isn't going to do something impolite seems to me to be a long-trousered job and a half. Some insight would be much appreciated.

Well, I think with dimmers sold into residential and light commercial settings, nobody is making much in the way of promises. That is, if you go to all the lighting dimmer websites you will see scant descriptions of what constitutes a CFL-friendly dimmer, and LED-friendly dimmer, a "universal" dimmer, etc. It's actually pretty embarassing. As far as the quality of the waveform, well, garbage in and even more garbage out appears to be the watchword. Good filtering requires non-trivial inductors and those are components that NOT in evidence in your typical dimmer. These things are built to be as cheap as possible.

All that said, this gentleman (Rod Elliott) has torn down the CLIPSAL in the video and claims that it basically is a FET-based dimmer that can operate in either forward- or reverse-phase mode, and will make the determination itself:

http://sound.westhost.com/lamps/dimmers.html

I have built a similar dimmer myself. It can do forward or reverse phase control, driven by a uC. (It could also do PWM which works nicely with incandescents and a good LPF and on the input AND output.) However, unlike the CLIPSAL people, I was not clever enough to have the dimmer determine which mode it should best operate in! Anyway, my project has been useful for experimenting with the topology.

Also, the CLIPSAL unit is obviously driving two FETS in half waves rather than one in a full bridge.

-- dave j

[Tek_TDS220]

Fancy format - I can remember when Dave did these videos in his garage.   Next he needs a female co-host, some informal banter, and a teleprompter.

[99tito99]

Hi Dave: Like the new format (2 thumbs up).  The back-and-forth between the “full frontal” view and the close-up seems to work well.  The background porn is not a problem, I just paused and got my eye-full and then continued.  Although, some said it is distracting, I say keep it and in fact swap out a new gadget every so often.  Besides, if someone is listening that closely to what you are actually saying they may have an issue (joke?).  Cheers, Mark * * *

[SmalltimePrankster]

Many years ago part of my job was to repair those Sharp IQs.  Really all that went wrong with them was the flat cable between the two halves and it was a real PITA to replace.  The post repair test process, as directed by the service book, was hilarious.

Test one was check that it powers up (so far so good).

Test two was to grip either end with it turned on and twist the case to see if the display stayed normal (ok, this test makes sense).

The final test, and you may not believe this, was to hold the unit 20cm above a flat hard surface and drop it so it (hopefully) landed flat and then check that it still worked.

A drop test.  Part of the standard service process.  Really.

[Juun]

Next he needs a female co-host, some informal banter, and a teleprompter.

This would be the end of it! 

[Stonent]

The new format is a definite improvement, although Dave now looks a bit like a TV anchorman. Perhaps some portentous music and pointlessly swoopy glittery animation at the front? As for the shelves behind - if a bunch of scopes can be wired up to show key metrics in real time (hits/sec, comments/min, Dave's blood pressure, swear index, etc) then it'll be much more Star Trek and thus much more to my taste.

I do hope someone has the circ for the dimmer, or something like that. In a past life, I was part of a team doing comparative testing of UPSs, which is a seriously hard job and one we really did have to stop working on rather than finish. I learned (well, was exposed to) a ton of stuff on that project, including just how mad mains electricity looks in a large building filled with mid-90s vintage IT running off second-generation SMPSUs. It's a very hard environment to properly appreciate, let alone design for, especially for a chap whose previous PSU knowledge stopped at four diodes, a centre-tapped transformer, a couple of caps and an excuse-me.

Designing a half-kilowatt universal dimmer that isn't going to do something impolite seems to me to be a long-trousered job and a half. Some insight would be much appreciated.

R

With the background and facing the camera, I think Dave now needs a red vest with company logos on it and subtitles if anyone catches the reference... 

[steve30]

I don't really care much for the idea of Dave sitting behind the desk. But it did work fine for the mailbag since we can see him while the mail is being opened.

It would be cool to get that Sharp organiser working .

Can the LCD on the calculator be improved at all?

[84GKSIG]

hey Dave I like the new video format for the mail bag. im gonna try send something to you for your mail bag if you like hopefully in the next couple of weeks.

[kcs]

MouseBiteFever, I took a closer look at your PCB. Your pads are smaller in width (14 mils instead of mine 17.5 mils). With those extra 3 mils (5 mils total), you can use solder mask between pins. I was following manufacturer recommendations for PCB layout and it seems that TI does not offer that for its package.
Well, we will see how hard it will be to solder that tiny IC when no solder mask is used. I should receive my boards very soon.

[timelessbeing]

I like the new mailbag format. Keep doing that. 

[99tito99]

Fancy format - I can remember when Dave did these videos in his garage.   Next he needs a female co-host, some informal banter, and a teleprompter.

Yeah, and a bow tie.  Cheers, Mark

[Laertes]

if a bunch of scopes can be wired up to show key metrics in real time (hits/sec, comments/min, Dave's blood pressure, swear index, etc) then it'll be much more Star Trek and thus much more to my taste.

Much better idea than a female co-host. 

[nixfu]

Fancy format - I can remember when Dave did these videos in his garage.   Next he needs a female co-host, some informal banter, and a teleprompter.

And an official "announcer" that says "Heeeeeeers Dave" and also a  band....don't forget a band.  They have to play the "mailbag jingle" or the "Teardown tune" whenever appropriate.   

[Monkeh]

Well, we will see how hard it will be to solder that tiny IC when no solder mask is used.

Piece of cake.

[silicon_ghost]

+1 on the new format. I like how it breaks up the video into segments.

[lapm]

Hey Dave, i like the new mailbag format... Big  for that...

[kolbep]

With the background and facing the camera, I think Dave now needs a red vest with company logos on it and subtitles if anyone catches the reference... 

What, you want him to join the EFF (A South African political party - The Economic Freedom Fighters - Who wear red Jumpsuits/Overalls with Red Berets even at Parliament mettings, Apparently to associate themselves with the hardworking, underpaid miners, etc in RSA)

?

[SeanB]

No Peter, he does a little more work than lifting up a Breitling and shouting slogans while eating. I think the reference is to a more American talking head.....

[electrolux]

I like the new format, it looks a lot better since the camera isn't too close to the box you're trying to open and you have more room to show the contents before changing to the usual angle.

I like it too, Keep it

[electrolux]

New format is nice, but are you sure you didn't do it to get your ugly head in the picture  

[tocsa120ls]

Be lucky you don't know why someone made a crappy ohmmeter in 1989. Did a quick search in the forum, either nobody caught it, or was too lazy to write it down - that thing was made in an accordion factory.

Why? Well, short answer is the Russians. Until 1990 East Germany, and my home country, Hungary were under russian administration - one thing about that was the so called "five-year plans" - basically, high-ranking officials "predicted" what people would want in the next five years, and how much of those things should be produced. We know today that the best computer in the world would not calculate that until the heat-death of the solar system, but hey, down a few vodkas and you make

- bus manufacturers manufacture 5000 prams per year (yeah, imagine a 15lb plaything next to the 20ton busses on the assembly line)
- agricultural collectives manufacture PC power supplies (hey, there was a draught that wasn't in the 5-year-plan, now how do you make money?)
- in Hungary, the Telephone Manufacturing Company made... wait for it... reel-to-reel decks (they do make a sound, afterall)
- accordion factories produce ohmmeters (I don't even...)

Funny thing, that cold war was.

[Alexei.Polkhanov]

Sometimes I kind of miss it - there was arms race, space race, nuclear race, everything race ... So much truly new, cool stuff was invented!!! All sorts of cool research was funded out of those huge budgets. Now technology news all sound like "there are rumours of better, slimmer iPhone..." -  WTF?

Nobody going to miss those 5-year plans and crappy multimeters that is for sure, but there were lot of very good and amazing things happening as well. I remember how generously research was funded when I was on first year of my PhD program - everything went downwards from then on. If governments don't fund fundamental research the who will? Corporations don't want to invest into something that may or may not pay off in 20 years. They only care about next year at most.

[jancumps]

I was scared like hell that the bomb would fall.

[tocsa120ls]

Sometimes I kind of miss it

Alyosha, you might have found the only good thing about it. Travel restrictions, rationing system, pointless jobs (so no citizens are without one), secret police (and not todays kind)... no thanks.
We only remember the good things about the old times. It's not offset by the bunch of other bad stuff, like...
you have a PhD. In those times that meant your kids couldn't go to university. 

[Stonent]

With the background and facing the camera, I think Dave now needs a red vest with company logos on it and subtitles if anyone catches the reference... 

What, you want him to join the EFF (A South African political party - The Economic Freedom Fighters - Who wear red Jumpsuits/Overalls with Red Berets even at Parliament mettings, Apparently to associate themselves with the hardworking, underpaid miners, etc in RSA)

?

No, I've never heard of them.

[Alexei.Polkhanov]

you have a PhD. In those times that meant your kids couldn't go to university. 

Huh?  High education was completely free and on top of that I was paid sort of like a salary while going to University from day 1 to cover my living expenses. Plus if you going to University right after school at 17 or 18 you get excluded from army draft. To send my kids to Canadian or US University I have to chip off at least $30K/year.

[phamuc]

Hello Dave,

I like the new mailbag format. Now you just need a group of geeks to clean the floor. 

[coppice]

Sometimes I kind of miss it - there was arms race, space race, nuclear race, everything race ... So much truly new, cool stuff was invented!!! All sorts of cool research was funded out of those huge budgets. Now technology news all sound like "there are rumours of better, slimmer iPhone..." -  WTF?

Nobody going to miss those 5-year plans and crappy multimeters that is for sure, but there were lot of very good and amazing things happening as well. I remember how generously research was funded when I was on first year of my PhD program - everything went downwards from then on. If governments don't fund fundamental research the who will? Corporations don't want to invest into something that may or may not pay off in 20 years. They only care about next year at most.

Not so long ago Bell Labs, HP Labs, IBM Labs and other commercial R&D centres did a lot of very basic research. It made them lots of money, but the money didn't come quickly. That worked when companies were run by their management. Now they are run by the stock market, and nothing long term is possible.