Monday, January 27, 2014

Teardown highlights from iFixit

Part of the homework this weekend is to read some teardowns at iFixit (each student was assigned 12 to read) and send me an email with a link to your favorite one, with a short explanation of why it's your favorite. Here are the replies that I've received so far:
  • Nvidia Shield and iPod Touch 5th Generation 16 GB
  • No one is going to buy the Nvidia Shield. But, the teardown is interesting as an example of the intersection of mechanical and electrical design. (The joystick potentiometers are surprisingly cool.) It's also a fairly complicated teardown, and an example of taking things apart in a reasonably reversible way. Also it has fire.

    Very few people are going to buy the 16GB iPod Touch. But, there are some fairly clever techniques used in the teardown. It also shows the power of teardowns as an analysis tool, finding the changes between this and the previous iPod model.
  • AirPort Extreme A1521
  • Apple products are well-designed in a way which allows you to easily forget that there are even insides, so it was kind of nifty to break into this aesthetically beautiful fortress. In particular, any engineer reading this is likely floored at how much empty space they left – why would they bother leaving several inches between the ports and the fan? It’s a nice lesson in aesthetic design: not everything has to be built for efficiency, and it’s okay to let the non-engineers make things pretty.
  • 2012 MacBook Air
  • Very impressive device. A neat feature is the "asymmetrical fan" that has different fan blade lengths in order to disperse sounds over a wide range of frequencies, reducing fan noise. Visually, the interior was very clean and crisp; most components, including the battery and PCB's were black. However, in classic Apple fashion, the 2012 MacBook Air was riddled with proprietary components, including pentalobe screws on the case in order to keep the casual observer's curiosity at bay.
  • Nikon D600
  • I had never previously thought about the complexity of such an opto-electronic device and could not have imagined how complex and densely packed the device is. Step 15 reveals the absurd number of EMI shields and other busses that are crammed into the case. You wonder what all those bits of metal could possibly be for until you see in steps 19 and 22 how boards and different ICs are carefully scattered across every surface of the exposed camera frame. It was neat to see the 24MP image sensor exposed, and Chipworks has some more details and SEM images of its design.
  • Pebble
  • The teardown of the Pebble E-Paper watch was pretty fascinating. The watch does not have any exterior screws, so the needed to pry the screen off of the front of the watch. They were actually unable to get the screen off without breaking it due to the amount of adhesive used in the design, which makes me wonder if this was an intentional decision to keep tinkerers out, or if it is just a result of being the first design they were able to come up with via their Kickstarter funds/timeline. Other than that, it was just a very thorough analysis which showed how compact of a design it is and identified all of the major ICs.
  • Xbox One Kinect
  • The Xbox Kinect is a really interesting piece of technology. Of course, it has a lot of neat signal processing going on, but the really interesting part is the sensor suite. This particular teardown actually focuses more on the IR blaster and camera assemblies since these are the functions that make the Kinect function. As the teardown points out, these assemblies are very sensitive and taking them apart was about "like a game of Operation." I find this to be a pretty bold move by Microsoft, considering that the purpose of this product is for people to jump around and swing their arms every which way. Not just do they need to worry about damage due to customer abuse, but I would imagine they also needed to develop a very specific and accurate assembly procedure to forego any damage during production.
  • Samsung Galaxy Note 10.1
  • I though the Galaxy Note 10.1 teardown was very interesting from both a mechanical and hardware standpoint. By reading the teardown, it is very apparent that the Samsung engineers designed the Note so that parts can be easily removed and taken apart. Unlike most electronics that are held together mainly by adhesives and press fits, the engineers at Samsung took the time to design the Note around screws and snaps. Similar the LCD screen can actually be removed from the glass unlike most devices. Therefore if the screen cracks, instead of replacing both the screen and the LCD display, just the screen has to be replaced. A cool feature about the hardware was that the EMI shielding (which are easily removed by screws) also serve as the Note’s heat sinks.
  • Keithley 199 Scanner Multimeter
  • I like it because, unlike the variety of modern phones or simple devices included in my section, this teardown really goes into details on components and what can be fixed. Additionally, it has some real depth that the modern devices just can't match which makes the actual dissembly much more interesting.
  • Orange
  • Just kidding.
  • HTC One
  • A few years ago I ended up repairing a few iPhone 3G's and 3GS and remember the difficulties with doing it. I thought it was interesting to see how much more difficult it's become since then to repair these things, to the point where the HTC One essentially has to be broken to even get inside of it. Beyond the continuing of this accessibility trend, it's always fascinating to see how much the cram into so little space and techniques I didn't know about to help with that, like copper shielding on almost all of the components for heat dissipation and grounding.
  • Nexus Q
  • My favorite teardown was of the Nexus Q, a strange failed hardware project of Google's. The guide was well written with a healthy dose of humor. The writer took the time to identify ICs and speculate on their significance. There were small interesting factoids included along the way, such as the country of origin of various parts. I also thought the geometry of the device itself was interesting. The casing is a sphere. The board layout had to be done in a way such that big components jutting out perpendicularly (like capacitors) were placed in the center, so that the whole thing could be sandwiched together between two shells.
  • Apple A7
  • At the very heart of the iPhone5 is its A7 processor, and this teardown stripped away another black box to see the silicon itself. The nature of the teardown for a teeny-tiny chip meant that all the heavy lifting had to be done with in lab rather than a work bench. The nanometer scale that the transistors had to be measured on gave a new gravity to this impressive device. The ability to cram so many functions into such a tiny space is truly astounding.
  • Macintosh 128K
  • The engineering of the Macintosh 128k is interesting because most of the pieces are slid together and held together with screws, so taking it apart is not very difficult. It is also an interesting tear down because it shows how technology has progressed in 30 years. The logic board is cool because there are no surface mounts, there are only through holes making it look very different than the boards we see today. I thought that the fact that the buttons of the keyboard were soldered directly to the board is funny because in current keyboards, the keys just pop off, and I think it’s just an advancement that I don’t really think about but is pretty important.
  • Compaq iPaq Pocket PC 3765
  • The Compaq iPaq Pocket PC 3765 is interesting to me because it was one of the few popular hand-held personal assistants that existed before smart phones combined their capability with cell phone service. I surprised by how easy the device was to take apart. Just a few screws in back and some snapping mechanisms hold the casing in place. They point out that though the company responsible for the product is Compac, both the processor and the control board are branded with HTC. I think that's particularly interesting since HTC makes so many smart phones now.
  • iPad mini Wi-Fi
  • The iPad mini teardown is interesting as Apple products are notorious for being designed to make it hard to open. The number of hidden screws and screws smaller than those in an iPhone 5It still surprises me how extensively glue is used to hold products together. Steve Jobs himself has mentioned that we "don't like to think of our products as glued together". The commentary on the choices for certain parts also make for an interesting read. The commentary on the design decisions like soldering the Lightning connector, or having the front glass and LCD assemblies separate, and how these decisions affect reparability gives me insights on to the implications of such decisions when building electronics. It is also cool to see that touchscreen still function after being taken off. Kind of like the electronic equivalent of a limb still moving after being detached.

Thursday, January 23, 2014

Gear teardowns

Assignment for Monday:
  1. Get a toolkit (if you don't already have one).
  2. Read Chapters 1 and 2 in "Troubleshooting Analog Circuits" by Bob Pease.
  3. Discuss the autopsy/teardown candidates with your lab partner (see exhibits A through Z in the administrative handout).
  4. Review the assigned teardowns at iFixit and send me an email with a link to your favorite one, with a short explanation of why it's your favorite. For example explanations, see last year's favorites.
  5. Watch the following video (a teardown of an Anritsu spectrum analyzer from Mike's Electric Stuff; see his YouTube channel for more videos).


Good stuff.

Wednesday, January 22, 2014

Monday, November 11, 2013

Voltmeter wiring correction at the Museum of Science

Yesterday, the family and I spent the morning at the Museum of Science, and the kids wanted to revisit the Discovery Center (mentioned in this post). With mild trepidation, I approached the second floor to see the circuits display, and I was pleasantly surprised, thrilled actually, to see that the wiring error had been fixed!

Close-up of the meter connections...
The voltmeter and ammeter are no longer in series! Very nice. I admit that I didn't think it would be fixed, based on the rationalizations in the comments of the last post, but I am very happy to see that it has been. Score one for engineering education! (By the way, it is a fun exhibit; my daughter really liked it.)

Tuesday, May 14, 2013

Voltmeter wiring error at the Museum of Science

UPDATE: Fixed!

This post isn't really about EE Prototyping, but it is about electrical engineering education, so I will post it here.  I spent Mother's Day at the Boston Museum of Science with my wife and kids. The kids had a blast, and we all had a great time, except for one thing...

In the "Discovery Center" there was a fun little electricity demo that let you construct simple parallel and series circuits with some magnetic, conducting building blocks.  There was a light bulb block, a buzzer block, and an LED block (that glowed green when the current flowed in one direction and glowed red when the current flow in the other).  Neat exhibit.  The power supply was mounted above the desk with the circuit blocks, and it let you choose to power your circuit with two, four, or six AA batteries.  A large knob in the center of the panel selected the power source, and two analog meters displayed the voltage and current.

Here's the setting for 3V output (2 AA cells):


Here's the setting for 6V output (4 AA cells):


Here's the setting for 9V output (6 AA cells):


See the problem? The voltmeter and the ammeter are both wired in series.  As connected, this circuit couldn't possibly work!  Here's a clearer schematic:



WRONG. The ammeter measures the current through the batteries, but the voltmeter must measure the voltage ACROSS them.  The voltmeter should be connected in parallel with the batteries, not in series. The panel should be wired like this schematic:


Better yet, to emphasize that voltage is measured across the power source, and that current is measured through it, the panel should be redesigned to look like this schematic:



Of course, the orange wires in the display case are just representational, and the batteries shown aren't really connected to anything (there is a wall-powered power supply behind the panel), but this error in the connection of the voltmeter should be embarrassing.  This exhibit would be a good chance to discuss "across" variables and "though" variables to more advanced students, but the "artist" who designed the panel blew it.

So sad.



UPDATE: See the responses in the comments below.

UPDATE UPDATE: Fixed!

Monday, March 11, 2013

Lab 4 layouts

The students have done a great job on the layouts for a wide variety of circuits from the Application Notes of Jim Williams. Here's a few of the projects:

Tachless motor speed controller (App Note 11, page 8)




Stabilized sine-wave generator (App Note 98, page 3)



Low-distortion sine-wave oscillator (App Note 43, page 33)



High-speed avalanche pulse generator (App Note 47, page 93)



Fast response V/F converter (App Note 14, page 4)



The Zoo Circuit, a micropower V/F converter (App Note 23, page 11)


The boards are on order, the parts are on order, and we're all looking forward to assembling the projects!

Tuesday, February 19, 2013

Lab 4

Forward Engineering. Using one of the schematics listed below, design a printed-circuit board to build a working copy of the circuit. Assignment:
  1. Look up the referenced Application Note and read the description of the circuit
  2. Compile a bill of materials and find sources for all the parts (including stock numbers and cost)
  3. Enter the schematic into the layout tool
  4. Produce the necessary PCB layout files for fabrication
  5. (Optional) Simulate the circuit in LTSpice (there are fewer weird ICs here)
The following circuits were all designed by Jim Williams, and the schematics appeared in application notes published by Linear Technology.
  • Tachless motor speed controller (App Note 11, page 8)
  • Fast response V/F converter (App Note 14, page 4)
  • Single-cell V/F converter (App Note 15, page 1)
  • Low-distortion sine-wave oscillator (App Note 43, page 33)
  • Complete AM radio station (App Note 47, page 52)
  • High-speed avalanche pulse generator (App Note 47, page 93)
  • Triggered pulse generator (App Note 61, page 21)
  • Stabilized sine-wave generator (App Note 98, page 3)
  • Output-leveled noise generator (App Note 106, page 11)
In choosing a circuit, be sure that you can find all of the necessary components.  Some parts my be substitutable, some may not.  If you have any questions about part substitutions, please ask. 

For a more complicated project, the following circuits provide additional challenges.
  • King Kong V/F converter (App Note 14, page 2).  The output frequency goes up to 100 MHz, and this circuit leverages fast components and requires careful high-speed layout.
  • Op amp with 120-volt output stage (App Note 18, page 7). With lethal voltages present, this circuit requires careful layout and construction to prevent circuit damage and engineer injury.  If you choose this circuit, power the circuit from a lower voltage (like plus/minus 48V) for initial testing.
  • Son-of-Godzilla amplifier (App Note 21, page 8). This amplifier has a bandwidth over 100 MHz and a tendency to destroy itself. Read the adjustment procedure carefully.
  • The Zoo Circuit, a micropower V/F converter (App Note 23, page 11).  The development of this low-power circuit is also described in one of his books.
  • 28VDC-to-110VAC sine-wave power converter (App Note 35, page 15). Again, with lethal voltages present, this circuit requires careful layout and construction to prevent circuit damage and engineer injury.  If you choose this circuit, power the circuit from a lower voltage (like plus/minus 48V) for initial testing.
Substitutions:
  • Substitute 2N3904 transistor for 2N2369 (for now, try other substitutions later)
  • Substitute 1N5711 Schottky diode for HP5082-2810

Monday, February 11, 2013

Op-amp applications

Today's lecture is a review of op-amp applications. There are several good references:
Here is a list of circuits you should know (and other interesting circuits):
  • Inverting and noninverting amplifiers
  • Summing amplifier (multiple inputs)
  • Differencing amplifier (two inputs)
  • Instrumentation amplifier (three op amps)
  • Integrator
  • Noninverting integrator
  • Single-pole low-pass filter
  • Single-pole high-pass filter
  • Differentiators don't work (*)
  • Lag and lead transfer functions
  • Negative impedance converters and gyrators
  • Low-pass and high-pass Sallen-Key filters
  • Analog computer block diagrams, which lead to...
  • Kerwin-Huelsman-Newcomb (KHN) biquad circuit
  • Tow-Thomas biquad circuit
  • Full-wave rectifier
  • Logarithm and exponential circuits
  • Temperature-compensated logarithm and exponential circuits
  • Multipliers (log/expo, light-bulb, servomotor, quarter-square, and PWM)
(*) Note that the simple differentiator circuit (input capacitor and feedback resistor) doesn't work because the op-amp feedback loop is unstable (there isn't enough phase margin). The TI Handbook says:
It should be mentioned that of all the circuits presented in this section, the differentiator is the one that will operate least successfully with real components. The capacitive input makes it particularly susceptible to random noise...
The first sentence is correct, but the second sentence is wrong. It's not a "random noise" problem, it's a loop-stability problem. The resistor and the capacitor introduce a low-pass filter in the feedback path, which reduces the phase margin (close to, or even below, zero degrees) of the op-amp loop.

Grr.

Thursday, February 7, 2013

Resistors and capacitors

Some notes on specifying passive components. Resistors and capacitors come in a wide variety of options.

For example, resistors types include thick film (resistive ink on ceramic), metal film (nichrome), carbon film, carbon composition, and wirewound. Important specifications and parameters include the power rating (constant power and pulse handling), tolerance, temperature coefficient, and voltage coefficient (nonlinearity). Notable parasitics are the series inductance, the parallel capacitance, thermocouple effects, and excess noise. See references [1] and [2].

Let's look at an example of specifying a resistor part: Panasonic thick-film chip resistors (ERJ series)
  • E24 and E96 series values
  • Sizes: everything from 01005 to 2512
  • Power: 1/32 W to 1 W (based on size)
  • Tolerance 0.5% or 1%
  • Temperature coefficient: 50 ppm/C to 300 ppm/C
  • Operating temperature range: −55C to +125C or +155C
Decoding the part number:


Maximum power rating is a function of package size (and type, tolerance, and temperature).  The power in a resistor is P = V2/R. Thus, the maximum voltage that can be applied across a resistor is a function of its power rating V = sqrt(PR).  For a 01005 resistor (0.031 watts) with value 100 Ω, this limit is only 1.7 volts. For a 2512 resistor (1 watt) with value 1 MΩ, this limit is 1000 volts.  However, the package may have a much lower maximum voltage rating (in this case, the limiting element voltage (LEV) is 200 volts).  The rated continuous working voltage (RCWV) is the lower of the two numbers sqrt(PR) and LEV.


The maximum power rating has to be derated above 70C.


Most Unnecessary Disclaimer Award: "These products generate Joule heat when energized. Carefully position these products so that their heat will not affect the other components."

Capacitors can be friend or foe. There are many different varieties of capacitors, and they all have their own strengths and weaknesses. See references [1] and [2].  There are a large number of properties that we can use to compare capacitors, including value, voltage, size, self time constant, temperature coefficient, dielectric absorption [3], effective series resistance and, of course, cost.

The choice of dielectric has a big effect on the quality and properties of the capacitor.
  • Bypass types: aluminum electrolytic, tantalum electrolytic, high- K ceramic
  • Filter types: NPO ceramic, polycarbonate, polyester
  • Sample-and-hold types: teflon, mica, polystyrene, polypropylene
In App Note 47 [4], Jim Williams has some warnings about bypass capacitor types (see pages 25 and 26). Figure 60 is downright scary.


Be aware of the effects of voltage and temperature.  Some types of capacitors undergo huge variations over the range of operating voltage and temperature (these plots are from the LT1763 datasheet). Note the huge variation of Y5V types.



Example 1: AVX tantalum capacitors (TPS series, low ESR)
  • Values: 0.15 μF to 1500 μF (E6 series, 1.0 1.5 2.2 3.3 4.7 6.8)
  • Sizes: 0805 to 2924 (see table of custom case codes)
  • Voltage: 2.5 V to 50 V (derate by 2/3 above 85C)
  • Tolerance 10% or 20%
  • Effective series resistance (ESR): 0.03 Ω to 9 Ω (see chart)
  • Operating temperature range: −55C to +125C
Datasheet tour:
  • Table of case sizes
  • Decoding the part number
  • Rated voltage and surge voltage (and derating)
  • Table of capacitance, voltage, and ESR
  • DCL, DF, ESR, RMS current, and RMS voltage
Example 2: Murata chip monolithic ceramic capacitors (datasheet dated Oct. 1, 2012).  Start with decoding the part number, for example GRM188R71E153KA01D:
  • GRM tin-plated layer capacitor
  • 18 size 1.6x0.8mm (0603)
  • 8 thickness 0.8mm
  • R7 temperature X7R type −55C to +125C, change ±15%
  • 1E rated voltage 25V
  • 153 capacitance 15,000 pF (E6 series)
  • K tolerance ±10%
  • A01 internal specification code
  • D paper tape
Datasheet tour:
  • Decoding the part number, pages 15–17
  • Actual capacitor listed on page 70
  • Temperature characteristics, page 119
  • Soldering and mounting, page 129

References:

[1] James Bryant, Walt Jung, and Walt Kester, "Passive components," in Op Amp Applications, Walter G. Jung, Ed. Norwood, Mass.: Analog Devices, 2002, ch. 7-1, pp. 7.1–7.24.

[2] Robert A. Pease, Troubleshooting Analog Circuits. Boston: Butterworth-Heinemann, 1991.

[3] Robert A. Pease, "Understand capacitor soakage to optimize analog systems," EDN, p. 125, Oct. 13, 1982.

[4] Jim Williams, "High speed amplifier techniques: A designer’s companion for wideband circuitry," Linear Technology Corp., Milpitas, Calif., Application Note 47, Aug. 1991.

Tuesday, February 5, 2013

Lab 3 part 1

The reverse engineering got off to a great start yesterday. Here's some quick photos of the students tearing into their chosen projects. (More updates later.)