EEVblog #443 - Mailbag

[mariush]

[poodyp]

That QWERTY thing is a myth really.

[mariush]

That QWERTY thing is a myth really.

No, it's not a myth but it's not quite as Dave says it. It comes from the days of the first typewriters:
 
From : http://en.wikipedia.org/wiki/QWERTY

The construction of the "Type Writer" had two flaws that made the product susceptible to jams. Firstly, characters were mounted on metal arms or typebars, which would clash and jam if neighboring arms were pressed at the same time or in rapid succession.[4] Secondly, its printing point was located beneath the paper carriage, invisible to the operator, a so-called "up-stroke" design. Consequently, jams were especially serious, because the typist could only discover the mishap by raising the carriage to inspect what he had typed.

The solution was to place commonly used letter-pairs (like "th" or "st") so that their typebars were not neighboring, avoiding jams. Contrary to popular belief, the QWERTY layout was not designed to slow the typist down,[5] but rather to speed up typing by preventing jams.[4][6] (Incidentally, there is evidence that, aside from the issue of jamming, keys being further apart increases typist speed on its own, since it encourages alternation between the hands.) Almost every word in the English language contains at least one vowel, but on the QWERTY keyboard only the vowel "A" is located on the home row, which requires the typist's fingers to leave the home row for most words.

So the keys are not quite in the optimum arrangement, because they had to compromise to minimize jamming. By the time they perfected the machines, people got used to the layout.
Computer manufacturers then reused the layout so they could sell them to secretaries as word processors..

see  "The secret life of machines" on Youtube for fascinating documentary about word processors if you're interested:


 

[Hypernova]

Holy shit another EEVblog follower in Taiwan! For the longest time I got the impression that I was the only Taiwanese here. Nobody I mentioned EEVblog to ever knew what I was talking about which mad me sad about the state of electronic hobbyists in TW.

As for the Republic of China thing, that's due to the TW government being the remnant  of the original regime that overthrew the Qing Dynasty. China's current name is just another case of them pirating everything plus a case of http://tvtropes.org/pmwiki/pmwiki.php/Main/PeoplesRepublicOfTyranny.

[NiHaoMike]

The piezo buzzer in that fire alarm can be very useful. It's obviously designed for high volume (but very narrow bandwidth) at the design voltage, but it can make a surprising amount of noise at a mere 5V or 3.3V. Remove the driver circuit (but leave the actual piezo in its holder) and simply connect it to an I/O pin on your microcontroller, ignoring the feedback pin if it has one. You can also characterize its resonant modes by connecting it to a function generator through a resistor (10k or so works well) and measuring voltage on the scope. (Try both the drive pin voltage as well as the feedback pin voltage.)

[codeboy2k]

So I decided to look up some of their patents, they are quite interesting to read, complete schematic diagrams and a description of the various control algorithms and flowcharts..

The patents are from 1997-1998 or so and relate to :
(1) using a single 2 wire DC loop for both DC power and signaling control of both audio and visual indicators, instead of the previously needed 2 wires for audio and 2 wires for visual (i.e. prior to their design and patent, 2 pairs (4 wires) were needed, using simple signalling where power is either applied or not. Applying DC power on the audio pair would enable the audio alarm, and applying DC power on the visual pair would enable the visual signal. Turn it off to silence the alarms)
(2) their 2 wire method uses short 100ms power drop-outs every second (i.e. on/off pulses) of the DC power signal to synchronize multiple chained alarm units in a building so they flash in unison and "whoop-whoop-whoop" up and down in unison throughout a building
(3) using similar voltage drop-out sequences at specific positions in time to turn off the audio, or turn of the visual, or both, from a central control panel
(4) an interface box and method of converting the old style 4-wire signaling to their 2-wire DC power and signalling control loop, to allow these alarm units to be retro-fitted into older installations
(5) a method of measuring inductor current in a DC-to-DC converter using an opto-coupler, to provide adequate charge on the strobe capacitor, in order to maintain UL mandated brightness of the strobe even in the event of DC power dropping to 80% of it's nominal value during an alarm
(6) a universal mounting backplate that fits single outlet boxes, dual outlet boxes, round boxes, square boxes and international 100mm boxes, thereby permitting an installer to inventory only one type of mounting backplate
(7) a method of preventing the installer from installing the unit upside down or right to left (instead of left to right) when using said universal mounting bracket. This is to make sure the unit is installed correctly to emit most of its light in the downward direction to meet UL visibility specifications.

This is not all of them. There were a few patents that I didn't look into.

[CHexclaim]

I remember a similar rectifier in the homemade car battery charger at home when I was a kid. I also remember the smell when it blew. My dad always said that they were horrible to work with. He worked as a field engineer with mainframe computers full of these precarious components.

Excellent information about the history of the brand.

Dave, I think that the beautiful postcard should be held in a portrait position with the lines of characters going downwards, but don't quote me on this, I am sure someone else will comment with more assurance.

I love mailbag..

[CHexclaim]

see  "The secret life of machines" on Youtube for fascinating documentary about word processors if you're interested:

This video is marvelous! Thanks. 

[poodyp]

Hence why I said it's a myth.

[G7PSK]

The first rectifier I ever had was a metal rectifier but a bit bigger than that one, it was made to run the arc lamps in a cinema projector.