From: Sean Breheny <shb7@cornell.edu>
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Date: Fri, 17 Jan 2020 11:43:21 -0800
Subject: Re: [EE]:: What do you wish you had known before you started with
	Electronics.
Thread-Topic: [EE]:: What do you wish you had known before you started with
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I've had much better luck with hot glue than Russell ;)

I use certain higher-quality (supposedly) glue sticks which melt at a
higher temp and have a very distinctive odor (I don't have the brand
handy). If I am bonding to plastic or wood and the surfaces are clean, I
have some projects which have used it 10 years ago and are still holding
fine. Used only for moderately structural stuff at no more than maybe 2 psi
(7kPa) tension or shear - no strong "peeling" moments.

On Thu, Jan 16, 2020, 4:28 PM RussellMc <apptechnz@gmail.com wrote:

> We have had discussions like this long ago (I think).
> I'll post this and see if there is any interest in an updated ramble. It
> might lead to a worthwhile summary. Or not. TBD.
>
> In January 2012 I answered a Stack Exchange question "What do you wish yo=
u
> had known before you started with Microcontrollers?"
> My answer was intentionally more along the line of  "What do you wish you
> had known before you started with Electronics."
>
> For reasons disparate the Q&A was locked long ago, which I think is a
> shame, as the subject is useful.
> My now locked answer is here:
> https://electronics.stackexchange.com/a/25294/3288
> I've copy & pasted my answer below. Formatting has been 'altered'.
>
> Lines [in square brackets] have been added just now.
>
> Much more could be said :-).
>
>          Russell
>
> _____________________________________________________
>
> RS232 is upside down
>
> [Logic 0 is negative wrt ground]
>
> Most of everything you will have problems with will be caused by "boundar=
y
> conditions" - stuff that happens as things get going or start stopping.
>
> Always initialise your variables. ALWAYS.
> And your interrupt vectors.
>
> Little endian.
> Big endian.
> High/low byte first.
> Left adjust N bits.
>
> Flags left still set when work is done (eg IRQ flags).
>
> Stack overf
> ck underflow.
>
> RTS versus RTI
>
> Watchdog what ?
>
> Simple interrupt driven timer real time round robin scheduler that looks
> like a full RTOS but can be understood and written as you go. Trivial and
> amazing.
>
> Microcontroller pin specs - Vout / Iout relationships. Vin limits. Holdin=
g
> pins near mid rail.
>
> Always define all pin states under all conditions.
>
> Thermal resistance.
>
> NEVER let a body diode conduct (or mayhap a few uA if you really really
> must) that your life shall be long on the face of the land - even when th=
e
> great satans come and tell you it will be alright and that you CAN safely
> use them for input clamping.
> [Even when eg Microchip application notes use body diodes for clamping hi=
gh
> high impedance mains inputs, believe them you musn't. Court the dark side
> do not]
>
> Absolute parameters and operating parameters in data sheets mean totally
> different things and must NEVER be used interchangeably (or at least not
> the former for the latter) that your days may be long ... etc.
> ["Typical minimum" does NOT mean "minimum" allowable and may mean differe=
nt
> things in different cases.
> eg LM741 [RIP] typical min operating voltage  is shown as +/-12V. It can
> legitimately be run on loweer without violating specifications. How much
> lower may be hard to tell]
>
> V =3D I x R. The V doesn't happen if the I isn't happening so drawing
> conclusions re V without I is pointless, or worse.
>
> Hex Schmitt inverters !!!! God's gift to DIY digital AND analog
> electronics. (74xx14, CD40106, ...).
>
> CMOS logic !!!
>
> Opamp common mode range.
>
> Opamp output headroom - high and low.
>
> [Opamp Vout drives to "almost ground" - implications, solutions, problems=
,
> ...]
>
> Voltage regulator dropout - ON TOP OF Vout min.
>
> Voltage regulator Iout min when relevant.
>
> Lead acid battery sulfation. Don't let it !!!
> [V_bat-la >=3D 12.6V ALWAYS]
>
> The utter magic of LiIon batteries, despite their drawbacks.
>
> The utter nasty chicaneries of NimH batteries, despite their nicenesses.
>
> [The benign loveliness of LiFePO4, mostly.]
>
> [Battery chemistry-very-variable temperature limits, high and low, charge
> and discharge, performance when near limits, work arounds, do not work
> arounds].
>
> LSD NimH (no, not lysergic ...)
>
> Adjustable current limit adjustable voltage power supplies for prototype
> life maintenance.
>
> MOSFETS !!!!!!!!!!!!!!!!!!! Yee ha
>
> Low Vgsth MOFETS and digital electronics and large loads. Yee Ha.
>
> MOSFET, 2-jellybean-transistor gate drivers.
> Why you NEED a gate driver.
>
> Tantalum capacitors die die die !!! (and they do)
>
> Input leakage current. What's that?
> Input off what ?
>
> Accuracy / resolution / linearity / monotonicity / ...
>
> Isochronous.
> Asynchronous?
> No, Isochronous.
>
> [Clock stability crystal / ceramic / RC / ...]
> [Aging. Worst case. Across range. Cumulative. ...]
>
> Asynchronous. 1 bit, 2 bit, 1.5 bit, more.
> LSB first!. First? YES! Start bit, stop bit, parity bit, forced parity, n=
o
> parity, do you know if parity is on?
> Bit sampling - middle of bit, samples per bit.
> [Accuracy with RC - absolute error per end, shared drift (temperature),
> resonator, crystal internal clock - old one and new.]
> Always more !!!
>
> Crystals shatter on high g./ Or just drift and jump.
> Or shatter.
> [Crystals shatter on high drive. Not so much an issue with IC driven cloc=
k
> circuits.]
>
> Hot melt glue fails. Always. Always ? *Always *! Weeks to months to just
> maybe years.
> [If you MUST use hot-melt glue with aims of long term retention, it MUST =
be
> mechanically locked through holes or slots s that when the bond fails the
> part is retained. This is a very poor system - but the best you can
> manage].
>
> Acid cure silicone rubber is a no no no no.
> [Neutral cure SR - very very useful]
> [AlkOxy "neutral cure] is cheaper than full neutral cure but is corrosive
> to bare copper (but not much else].
> Thermally or electrically conductive epoxy is filled with X - you can fil=
l
> it too.
>
> Silicone rubber and cornflower say 50-50 to start. Try it, you'll like it=
..
>
> Heating a large pottle of fibreglass resin on a cold morning may make it =
go
> off faster but THAT fast ??? !!!!
>
> Tin whiskers.
>
> If they say ROHS their magic machine will spot your non compliance
> instantly.
>
> Learn to solder. Well.
> Note that solderability can vary very very greatly.
> Bad solder is a waste of calories and not worth sharing your life with.
> ALWAYS clean / abrade a bare board that has sat around a while before
> soldering - time and stress saved can be monumental.
> Learn to NOT catch falling soldering irons.
> Learn to kick falling soldering irons while grabbing their cords, if they
> have one.
> Learn not to drop soldering irons.
>
> Nd2Fe14B (and similar "rare earth") magnets are great fun BUT -
> They can do you a very serious injury.
> A good one can take out a wallet of magnetic cards at a single bound. The=
y
> shatter chip and break with ease.
> The US process ones are significantly inferior in field strength to the
> Japanese process ones.
> Provide up to about 0.5 Tesla across an airgap of about half material
> thickness.
> Magnetic field drops as inverse SQUARE of distance from one pole but two
> poles are always involved so it looks like 1/d^3 at a distance.
> [They corrode with time - fast enough to merit providing some sort of
> conformal coating in environmentally adverse conditions. This is probably
> usually due to breaks in the plated surface. Handle accordingly.]
>
> Much more ... :-)
> --
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> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>
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