Hi, welcome to everyone's favorite segment, the mailbag! Where People just send me random stuff! And Unfortunately, it's built up a bit again, uhh, just a little bit... Hmm. Camera Can't even pan up that high. Well, we may as well start with something easy.

A Postcard. I Love postcards, and look at this a lovely little town in Innsbruck. And I know where that is. That's not in Australia it's in Austria.

Beautiful. Love How they've captured the sun on the cliff tops up there. Brilliant. Lovely Little town.

Here We go. Who's it from? Hi Dave, greetings from Austria . We Are two enthusiastic hobbyists, we attend the Higher Technical College of Electronics in Innsbruck, and we really enjoy your blog! Thank you very much, keep doing all that good work. Two Austrian Fans, Simon and, I believe it's Joseph, is it? Thank you very much Simon and Joseph.

P.S. We Like it when you say Australia, not Austria. Not Sure what the stamp is. I'm not even going to pronounce that kind.

Well, it's a painting, is it? So Is it a stamp of famous painting, perhaps? I Don't know! And, if you do want to send me stuff, send it to Dave Jones, that crazy Aussie bloke. PO Box 7949, Baulkam Hills, BC, New South Wales, 2153, Australia. Not Austria! Next Up we have one from the Republic of China, ROC. Love it! It's from Chiang Liang-Chih.

With a silent H, I'm guessing. From New Taipei City. Hi To all my fans in New Taipei City, in Taiwan. Never Been to Taiwan.

Not-- you know, yeah, it's a republic of China, but I Don't know if the Taiwanese people like the Chinese people very much, do they? Or vice-versa. Not sure. I Don't know. Does Anyone know about the politics and history there? Let's check out the stamp.

There We have ourselves a lovely looking bug there from the Republic of China. I'm sure that's it's botanical name, is that the correct term? I don't know. Yeah, I give up. And Is that how you write Australia in Taiwanese? I don't know! Or maybe it's "Not Austria", perhaps.

Hmm. This thing open and see what we have inside. Stuck, it's stuck. What is it, a-- Ooh, we've got a card! Isn't that lovely.

Thank you very much! I Have no idea what it says, but nice artistry on there. Nice penmanship. Beautiful card. And What do we got? We Have a note.

Oh, that's part of the-- oh yes. Okay, that's the embossing part of the card stuck on there. Let's have a look. Tada! Hi Dave, thanks for the wonderful EEVblog, thanks.

Chinese New Year of this year is the snake. The Year of the Snake. And I'm waiting the spring season coming soon. Well, I Live in Taiwan, Northern Hemisphere whose seasons are opposite to yours.

They are indeed. I Went to working holiday in Australia for one year. Great Country, great people, and got kind of surprised to see your inspiring video about electronics. Thanks again! Wish You have a joyful year.

No worries. Thank You very much Chiang! Woohoo! Happy EEVBlogging. Thank you very much! And Let's start out with a yank. Michael Bruss.

G'day Michael! He's from Davis, in California. 95616. Ah, weird-ass 5-digit postcodes there. We've only got 4 digits in Australia.

And I can't quite read what is in the box. So Bit of a mystery. So Let's crack it open. And have a look.

I Think this is a fairly recent one. I'm opening these in kind of random order. Haven't really-- there's quite a F-- there's a few that have been sitting here forever, because I know what's in them and they will require a bit of work. So We have a note.

Might Read the note. Should We read the note first? No, let's go straight for the goodness. Here we go. It's...

What is it? Oh. Oh! It is-- oh! A Selenium Rectifier! I think he uhh remember somebody uhh messaging me or emailing me about a selenium rectifier from Federal. Really Old-school stuff. Aww, wow.

We're going to have to test this. Hi Dave. Enclosed is one new but vintage Selenium rectifier. made my Federal Telephone and Radio.

A Little bit about the company and selenium rectifiers is below. Feel Free to test the rectifier to destruction. Oh, I Don't know, it's-- it's too sexy for that. Aww.

However, Be aware that these devices can revenge themselves on their tormentors.. Sometimes When they fail, they emit a cloud of toxic selenium-containing smoke. Mmmm. You Have been warned.

The Voltage rating of selenium rectifiers can be deduced by counting the plates. It's 20 volts per plate. 20, 40, 60, 80, 100, 120, 140, 160 volts. There You go! Current Rating depends on the area of the plates and the thickness of the selenium coating..

Cores are either aluminium or steel , aluminium or steel. The Ones I've sent you has non-magnetic plates, so are assumed to be aluminium. It's light enough, yeah. I would assume they're aluminium.

Absolutely. Al Foil, by the way,, not aluminium foil. Confuses The hell out of the Yanks. Selenium Rectifiers are probably the second-oldest solid-state electronic devices.

Yep, I Wouldn't doubt it. The oldest being the Galena crystals used in early radios. Whoa, man. Now We're testing the old Greybeards.

The Concept of using selenium as a diode arose in the late 19th century, but commercial production did not begin until the early 1930s. Selenium rectifiers were a big hit, replacing less reliable, more fragile, heat-generating vacuum tubes.. Eventually, Germanium and then silicon replaced selenium, and I Don't think there is any valid use for selenium rectifiers today outside of keeping vintage equipment operational. I Really enjoy your blogs and have learned a tremendous amount from them.

My Wife and I visited Sydney a couple of years ago and loved it. Geeze, everyone's been here. Fantastic. But The flocks of flying foxes at dusk were a little spooky.

Keep Up the good work. Were They flying foxes or were they bats? Hmm. Mike Bruss from Davis, in California. A Little on the history of Federal.

Oh, awesome! The Original Federal name came from Federal Telegraph Company, started in the late 19th century in California. Eventually, through a series of mergers, yeah, no surprises there,. happens today, God, are there any companies left? Federal Telegraph Moved to Buffalo, New York, and changed its name to Federal Telegraph and Telephone, a.k.a. Federal T and T, in 1909.

Lee De Forrest, yeah, everyone should know that name. Co-inventor of the vacuum tube, worked for awhile as a designer for Federal T&T. There You go! Didn't know that. Trivia question at the pub.

Federal T&T had more than one division, one was called Federal Recorder which produced phonographs, and records. In The late 1930s Federal Recorder appeared as a brand of similar equipment produced by Wes Gardner of Illinois. Which is still in business today as Weds Gardner Electronics. There you go, outlived him.

Not sure if Wells-- Wells Gardner. Did I say Wes? Wells Gardner. Acquired Federal Recorder from Federal T&T or started it as an independent brand of their own. And We're not done yet.

Geeze, is this stuff in Wikipedia I wonder? I Don't know. If not, it should be! Another Division was called Federal Telephone and Radio, which produced electronic components like selenium rectifiers under that name, and complete radios under the brand Federal Radio. Another Division of Federal T&T was Buffalo Radio Station WGR. "And this is WGR playing all the hits from the 1920s" ...which is still in operation today.

The GR in WGR stood for George Road, who was-- Rand. Man, I can't read and do this video and look at the screen, do everything at the same time. Confuses me. I'm male, you know.

Um, who was a large investor in Federal T&T. George Rand was part of the Rand family of Rem-- Remington Rand fame. Yes, people should know that name. Which produced office equipment, and eventually the Univac computer.

Remington Typewriters were the first to use the QWERTY keyboard layout,, which we are still cursed with today. Yeah, because if people don't know,, the QWERTY keyboard was designed to slow us down! Because The machines,. So the urban myth goes, that the machines were so slow back then, they had to arrange the keyboard in some convoluted layout and they came up with the QWERTY one to try and slow people down, But hey,, now they do! You know 200 words a minute. T&T was acquired by ITT Corp.

in the late 1920s and produced components and equipment under its own brands until the 1950s, when the Federal brands were replaced with the ITT brands. Ahh, there you go! Thank you very much Mike, that was absolutely fascinating! And If this stuff-- if this info is not in Wikipedia, it-- somewhere, it damn well should be! Can The EEVblog now be used as a resource? Because I've read this out and oh,, EEVblog's a respected engineering resource! Does This now become official history? I Don't know! Now Of course, if memory serves me correctly,, these plates are going to-- these have quite a high drop, like in the order of like a volt per plate, or something like that. So Really, there's no point measuring it with the diode range of a regular multimeter,. there's-- you know, we're just not going to get anything with so many plates in there.

What is it, 2,, 4,, 6,, 8 plates. So, really all we can do is hook it up to a power supply with a series resistor, and we'll see if we can get this thing working. Now I've got it hooked up through a 32 ohm load resistor here, got it hooked up to my bench supply. Measuring The current here, and measuring the voltage across the rectifier diode here.

It's got positive on there, so I Assume that's the anode. So We'll hook it up and see. Now I'm at zero volts at the moment, as you can see. Let's wind the wick up.

We are getting-- you'd expect no current flow until you reach the-- almost near the voltage-- no, nothing. 8 volts. No. Have We got it back to front? Looks Like we've got it back to front.

Wind The power supply all the way up. Nope, that's as far as it goes, 22 volts. We Have it back to front, folks. So Of course we haven't got a high enough voltage to break it down.

Well, I do, but I'm going to save it for a separate video where I can characterize this thing properly. We Just want a simple forward voltage drop measurement. So It looks like that is back to front. Alright, I've got it the other way around now.

Negative is connected to the positive there. And By the way,, this is, if you want to know, this is 450 milliamp rated, 160 volts of course. Got it back to front. Let's wind the wick up.

We've got no current of course. Nothing yet-- hey,, there we go. It's starting to increase. There You go, because of course it's not just a, you know, a sharp curve.

A diode-- characteristic curve of a diode is-- doesn't just suddenly turn on. So We expect it to saturate around about 8 volts. You Know,, that was only a rough rule of thumb, really. But It looks like, hey,, we're up to 15 volts on the supply now, by the way.

Yeah, sorry I can't show the supply at the same time, but yeah, 15 volts on the supply. So That looks like the diode is now working and we're getting up to 300-odd milliamps. And We're up 22 volts, the supply is at maximum. 22.5 volts, 7.7 volt drop.

There You go, it works!. It's a Diode. Woohoo! So Thank you very much. Mike.

That is absolutely fascinating bit of vintage tech there. And I'll be sure to do another video where I try and characterize this thing a little bit better. I won't let the magic smoke out of it though. of course, that would be a shame.

Look At-- it's just a thing of beauty. It really is. I Can remember seeing my first selenium rectifier as a kid, like I don't know I was probably 8 or something. And I had no idea-- like you know, I knew about diodes, fine, whatever, and I took apart this old battery charger.

You know,, 12 volt lead-acid car battery charger. And It had a couple of these plates in there, and there were in series with the thing and I thought "that-- you know,, what the hell is that?" and of course I didn't have any info on it at the time. None of my books mentioned any sorts of these-- I didn't even-- you know-- had never heard of selenium rectifiers before, or plate diodes, or plate rectifiers or whatever you care to call the things. But I sort of knew it was-- it had to be operating as a diode, but I didn't know how.

And, well, I couldn't just look up Wikipedia then, geeze. No, folks,, no such thing back then! So all I had was the info in my books, and they just has, you know,, solid state, germanium and silicon stuff. That's all we had, really. So, geeze.

I don't know how long after that. I finally figured out, you know, I Finally realized that this was one of these selenium rectifiers. Anyway, very confusing when you're a kid and you see something like that in there. Because You couldn't buy it at your local Tricky Dick's store.

That's for sure. Anyway, thanks Mike, fascinating. Next Up, package from Maxey Isaac, in Mount Juliet, in TN. Which I believe is Tennessee, stand to be corrected.

He did send it to That Crazy Aussie Bloke. And Description of contents: alarm. Well , okay! 5 bucks worth of alarm. Let's check it out, shall we? No stamps, but we do have-- look at this! Nice looking badge slash sticker.

Wilson County Emergency Management. There you go, I Guess he's part of Wilson County Emergency Management. Beauty. Hazmat.

Well, hope there's nothing hazardous in here. So Let's whip it open and... See what we've got. Tada.

An Alarm! We Have a note. What is it, like an alarm panel? It didn't go off when I opened it, that's the main thing. Hi Dave! I Love your blog. It's been a great inspiration and is an excellent source for getting deeper into electronics design..

I Used to work for a local Federal Emergency Management branch by the name of WEMA. Isn't it FEMA? Sticker on the box, installing commercial fire alarm systems and warning sirens. When I left I Was left with a lot of interesting equipment, so I thought I'd send you something for the mailbag teardown! Thank you very much. In The bubble wrap is a Wheelock AS-24MCW notification appliance, ooh, for a commercial American Fire alarm system.

Its input is 24 volts DC, and if you power it up, be warned. it's loud! I Don't think I'll do that. I think I'm already loud enough here in the lab, I'm not sure what my neighbours think, and it is during 9-5 working hours here. Hmm, better keep it down.

This is a horn strobe enabled appliance, but once the strobe is broken due to it taking a fall about a year ago when it was being removed. Thanks very much. Thank you Isaac! Oh, he's got a YouTube username. spectrHz.

Awesome! Let's check it out. So no, sorry, I'm not going to power it up. Might Open it up, have a look in here. but that's about it.

Aww. Yeah, it's broken all right. Clunk, clunk clunk. Alright.

It's well and truly broken off in there. Aww. So I assume-- Fire! Fire! Fire! Warning Will Robinson! Um, I Assume that we just get our screwdriver in there to-- yeah. Seems to be the go, to whip that out.

Yeah, okay. No, there's no screws there, right? No, I'm not imagining things. Doh, I Completely missed the screw on the front there. Geeze.

I was attacking that with the biggest screwdriver and, oops., There We go. Tada! Too Easy. Ooh, flip flip. Woo, we have a board.

And that looks well and truly like a single-sided phenolic-based board. It's not your usual fibreglass type by the looks of it. Got A couple of jumpers here, which set something. And surface mount, of course.

Single-sided board, but they required some surface mount parts. Couple of diodes there. Some sort of regulator or transistor over there, and it looks like we have one DIP packaged chip on the top, and yeah!, Not A huge amount inside here, as you'd expect. But Check out the chip! They've got it Bre-- their own brand, Wheelock Inc.

Which is not unusual, to see chips personally branded with the company's name, it'll just be an off the shelf micro or something like that,. And of course, you'd pay a little bit of money, and they will re-label them for you. But Look,, that's a bit more unusual. A Wheelock Brand cap! Of Course, it's not their cap, they don't make caps, I'm sure of that.

They've just bought it from someone else and that's the storage cap for the flash strobe of course. Massive inductor over here. Couple of power resistors down in there, and looks like it's got a mode switch which does something. No idea, not labeled.

But yeah. Not much to it at all. We've got ourselves though,. look at that.

There we go, little MOV. On the input there. That's the 12 volt input directly there. Or 24, was it? Did he say? Yeah, 24 volts input.

So they've at least got a MOV protection there. They've got a ceramic resonator there for the-- little 3 pin of course,, ceramic resonator. for the microcontroller. So It's probably like a little PIC or something like that.

That is about it. Not Terribly exciting. Well There we go,. there's the label for the switch.

There we go, 75, 15, 30, 110. I Assume that's some sort of rate. Maybe a strobe rate timer thing? I don't know, something like that? But Although it's not very interesting,, these are good to scrap because you can actually reuse these strobe circuits. So, you know,, very useful to have one or two of these lying in the junk box.

Just for hacking purposes. I Like it. Thank you very much? Isaac! Ahh, there we go,. yep., 15, 30, 75, or 110 Cd.

I Assume that's candelas. So that's the-- I assume the brightness of the strobe light, presumably? 75 dB SPL, that's not screamer loud, really. So But yeah,, look. It's interesting-- it's all UL listed, it's got to meet various approval standards.

And Well, what the hell are they patenting this thing for? You've got to be kidding me. What's patentable in there? Next Up,, we have something from the old dart, Australia. Not Austria! Piss Off even more people again with another mention of it. Just "electronics"! 10 bucks worth.

It's from the old dart because it's Her Majesty's Royal Mail! Whoa. And They want to remain anonymous. Content-- big arrow, contents, Electronics. Well, I'd Hope so, this is the Electronics Engineering Video Blog! So Let's open it up.

Well, it's the Electronics Engineering Video Blog, and here one of my most popular segments is me opening my bloody mail. Can You believe it?? Oh, it's that crap again,. it just gets everywhere, I Hate this stuff. It's horrid.

If You don't open it prop-- if you don't keep it sealed, it just aww, it just blows everywhere. We Have ourselves a note, and we have ourselves... looks like several items. Ahh, good old handwriting.

Look at this, I Love it! Brings Back memories. Hi Dave, thought that you might like something a little different to take apart. I've not seen you work on anything like these yet. Enclosed are airbag control ECU and lane guidance camera out of two recent Hyundai cars, both of which have prematurely reached their end-of-life by becoming too-- friendly? with roadside barriers.

I Love the blogs, they are really interesting and informative. Keep up the excellent work. Have Fun! I Always do! Thank you very much Joey. Umm By Coincidence, I have been trying to get one of these airbag controllers off eBay.

I Have been hunting around for quite awhile trying to get one of these things. But I Haven't been trying too had, obviously, and I'm a tight-ass you know, I Don't want to pay like a hundred bucks for one or something like that, just to rip apart. So Awesome! Thank You very much, Airbag Control Unit. This will make an excellent Teardown Tuesday, I'm obviously not going to do it today.

And Check it out, is that like Arabic or something? Excuse Me: if I've got your, you know, language wrong there, whatever it is. But it looks kind of, you know, Arabic-like to me. But, there you go. It's a TRW airbag controller.

Faaaaantastic. That's going to make for a good teardown. Because These things have to be ultra-reliable, so there'll be, you know, I mean, just the approvals which go into thing, and it does look like we can actually open it with some Torx screws there perhaps, and it should just pop off. It's hopefully not potted, because that was almost-- always my fear, I got one of these things and, you know,, completely potted, and I don't want to have to, you know,, etch away the potting and all that sort of stuff.

So, hmm. Maybe A sneak peek? Hmm. I have a screwdriver... So We'll have ourselves a sneak peek here,, will we? Lift The skirt up.

Tada! It ain't potted folks! Brilliant. Now It looks like you can't just lift that board out, but you can prise it out because look,, the connectors are not soldered. There You go,, they've got these press-fit pins on these connectors. And Yes,, they're-- they are actually reliable.

Well, they have to be to be used in a high-vibration automotive application like this with, you know,, temperature extremes and all the rest.. So They haven't soldered in that connector there at all. They're just the press-fit type, and also looks like they've got some other parts up there, which are also press-fit in. There You go.

So that I am going to leave for a Teardown Tuesday. So You don't get to see the bottom. Ooh, there's a programming pad by the looks of it. Programming slash test pad.

Ahh. What's underneath? Hmm. Look Down there, we have a whole bunch of vias. Under a chip, some sort of heat sink, thermal pad on the bottom of a chip.

Hmm. Interesting. Sorry, that's for next time. Here We have the lane guidance camera.

And Doesn't this look funky. Aww Man,, that's got spaceship written-- like shuttlecraft, written all over it. Does A shuttlecraft make that noise? I Don't think so. No.

It's like silent. Because it's in space. Pigs In Space! Captioned by Sen.