Chip with simple program for Toy

[John Popelish]

BradBrigade wrote:

Hi,

First of all, I'm trying to figure out how switching power supplies
work (the ones in PCs). I've found very basic info, but I want more
technical stuff. If anyone has some good links please let me know.
These are questions I have yet to find an answer for.

Anyway, here's my question. One thing I read was that the output
voltage of the supply is fed back to the PWM which changes it's duty
cycle accordingly to keep the output voltage constant. But I thought
that the input-to-output ratio of a transformer is fixed. If the PWM
is outputting 100V at 20KHz to a 10:1 transformer, you get out 10V at
20KHz, right? What does it matter what the duty cycle is? It's still
100V at 20KHz. What am I missing?

If the transformer is a voltage output (produces some ratio of the
primary voltage when the switches are on) and zero the rest of the
time), then, yes, the peak output voltage is essentially independent
of the duty cycle. but those kind of transformers also require an
additional LC filter that outputs a voltage about equal to the average
input voltage, not the peak. Holding the peak voltage for a smaller
part of the cycle lowers the average voltage.

In supplies, where the transformer acts as an energy storage device
(apply input voltage, till the primary current ramps up to some value,
then cut the primary current, forcing the stored energy to reverse the
winding voltage and go up till an output rectifier connects the
transformer secondary to some storage capacitor). the average energy
throughput depends on how high the energy each charge-discharge cycle,
and how many cycles per second, and if the stored energy is all dumped
each cycle, or only some of it (whether or not the primary switch is
left off till the transformer dumps all its magnetic energy, or is
turned back on while the dump is in progress).

Second, why does a switching power supply break without a load?

Break? As in Kablooie? I don't know about that, but many
malfunction, because the control loop gain is dependent on the load
current. That is, the gain goes up as the load decreases. Stability
requires that the loop gain fall as frequency rises, so that before
the frequency is reached where the loop phase shift swings by 180
degrees (compared to low frequencies) the gain has fallen below 1, so
that the negative feedback (converted to positive feedback by the
extra phase shift) cannot generate a self sustaining echo.

Third, in all my years in electronics, I have never used a choke, now I
see them all over these power supplies. Can someone clue me in about
what they do, and why they are in these things?

There are just inductors. They store energy proportional to the
inductance and proportional to the square of the current passing
through them. Once you get up into significant currents, they become
as useful and necessary for energy storage as capacitors. Whereas
capacitors pass current in order to control the rate of change of
their voltage, inductors generate voltage across them to control the
rate of change of the current through them. If you want to absorb
current pulses and stabilize voltage, you use a capacitor. If you
want to absorb voltage pulses and stabilize a current, you use an
inductor. And we are back to that averaging filter that is needed to
smooth out the current from that pulsing voltage, variable duty cycle,
constant peak voltage rectified transformer so that it can be
connected to a storage capacitor where the voltage is to be regulated.

I appreciate any info at all. Thanks a lot.

 

[Rich Grise]

On Sun, 29 May 2005 05:41:02 +0000, Ban wrote:

Cynabar wrote:
Greeting all, I would like to know if anyone has any info on a video
distribution amplifier, such as the PCB layout or overlay? I have one
from Elektor, but am looking for another.

This is to assist me in the understanding and drawing the things in
AutoCAD.

Thanks for your time

I found the OPA692 an exellent IC to drive many video outputs(10)
simultaneously.
http://www-s.ti.com/sc/ds/opa692.pdf
You do not write how many outputs you want, what supply is available and
what kind of assemby you use (through hole, SMD, wave, reflow). All
require a different layout. Autocad is not good for layouts, it cannot
make the required processing to produce Gerber files. It also cannot link
to a schematic or netlist and doesn't have any suitable libraries. I
recommend Eagle(cadsoft) which is free for the size of board you will
need.

Thanks, Ban. I was simply going to say, "Whoever talked you into trying
to do electronics with AutoCAD is insane." But I did look, and it looks
like they're trying to do it - but heck, for the schematics you could
do with AutoCAD, you might as well use PC Paint. ;-)

Cheers!
Rich

 

[John Fields]

On Sun, 29 May 2005 17:05:16 GMT, Rich Grise <richgrise@example.net>
wrote:

On Sun, 29 May 2005 05:41:02 +0000, Ban wrote:

Cynabar wrote:
Greeting all, I would like to know if anyone has any info on a video
distribution amplifier, such as the PCB layout or overlay? I have one
from Elektor, but am looking for another.

This is to assist me in the understanding and drawing the things in
AutoCAD.

Thanks for your time

I found the OPA692 an exellent IC to drive many video outputs(10)
simultaneously.
http://www-s.ti.com/sc/ds/opa692.pdf
You do not write how many outputs you want, what supply is available and
what kind of assemby you use (through hole, SMD, wave, reflow). All
require a different layout. Autocad is not good for layouts, it cannot
make the required processing to produce Gerber files. It also cannot link
to a schematic or netlist and doesn't have any suitable libraries. I
recommend Eagle(cadsoft) which is free for the size of board you will
need.

Thanks, Ban. I was simply going to say, "Whoever talked you into trying
to do electronics with AutoCAD is insane." But I did look, and it looks
like they're trying to do it - but heck, for the schematics you could
do with AutoCAD, you might as well use PC Paint. ;-)

---
Winky noted, but, hardly. Everything I post which is non-ASCII goes
through ACAD on its way to .pdf, and I doubt whether you could get the
same results with Paint.

--
John Fields
Professional Circuit Designer

 

[w_tom]

Peter discusses (among many good points) the feedback
circuit in switching power supplies.

A power supply failed repeatedly in the field (I later
learned was also failing in the shop; but the failure was
ignored). The feedback optocoupler required a gain of 150. I
also learned that finding gains of 150 was all but
impossible. So the bean counters installed a lower gain
optocoupler. Therefore the power supply would sometimes -
rarely - but sometimes not power up and sometimes just
shutdown arbitrarily. IOW the power supply was 100% defective
- but was shipped because it usually passed tests. With
insufficient feedback, it was unstable - failed
intermittently. Cost thousands of dollars to replace that
defectively manufactured power supply.

Power supplies break for many reasons. This manufacturer
blamed insufficient load to avoid admitting the real problem.
I'll never forget nor forgive that company. They tried to
claim it was due to insufficient load when even their own spec
sheets said that load was sufficient.

Feedback is a concept taught in control systems. Like
filter design, the power supply designer must also have
fundamental comprehension of feedback control loops.

The user need not understand these technical issues. This
is where manufacturer spec sheets, manufacturer reputation,
and workers with power to flag problems are so much a part of
the system design process. But a power supply design is quite
complex - for something regarded by users as so trivial.

PeteS wrote:

There are excellent resources for switching power supplies at all the
major manufacturers (TI, Linear Tech, Maxim and others).

One of my favourite design notes is from Linear Tech:
http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1142,C1114,P1134,D4162

(AN-73 [pdf] at http://www.linear.com/ should the link not work). This
shows the basic principle of the Switchmode power supply using a
specific device as an example, with the coil used as (as noted) an
energy storage device.

As to why some switching power supplies 'break' with no load, I would
agree it could be poor design, although to be fair to the designers
they may be designed for a specific load. Much depends on the specifics
of the type :
Topologies:
Buck (Step down)
Boost (Step up)
Buck-boost (inverting, usually)
SEPIC (step up and step down - for isntance, generate +5V from a
nominal 6V battery that may have an actual range of 4V to 7V)

Mode:
Current. Inductor (or switch) current is controlled directly
Voltage. Output voltage is controlled directly
Generally, current mode controllers are insensitive to *input voltage*
variations and voltage mode controllers are insensitive to *output
current* variations.

A switching power supply (actually, any regulated power supply) is a
closed loop system that has various (and numerous) filter elements in
the loop. To get regulation employs negative feedback (i.e. an output
variation causes a change at the input such as to [partially] negate
the output variation).

What makes negative feedback negative is the effective phase of the
feedback signal. The filters in the loop add their own phase
characteristics, and if not carefully considered cause sufficient phase
shift in the loop to make the negative feedback positive - giving an
oscillator if it happens at unity gain. This is one of the [many
possible] things that can happen at no load.

Feedback loops of this type have many analogies - the most basic
principles are found in servo theory.
For an excellent app note on loop compensation (the art of keeping
negative feedback negative) for a current mode controller, see
http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1042,C1143,C1083,P1735,D4165
(AN-76, once more from http://www.linear.com/ )
For the filters, the relevant equations

Capacitive filters:
Fx = 1/(2*pi*R*C) where R is the equivalent resistance of the ffilter
and Fx is the Frequency at which the difference between input and
output is 3dB, which is also the point at which the phase difference
between input and output is 45 degrees. The phase and relative
amplitudes may be either leading or lagging depending on the filter
configuration (a leading phase filter is known as a zero, a lagging
phase filter is known as a pole)

Forr voltage mode controllers, there is a 2-pole filter at the output,
given by 1/(2*pi* [sqr(LC)]) where L is the output inductor and C the
effective output capacitance. At this frequency, there is 180 degrees
of phase shift at the output.

Each pole (or zero) has a phase response of 45 degrees per decade, and
an amplitude response of 20dB per decade (alternatively, 6dB per
octave). (Note to others - I realise the filters may be -45 or +45 and
amplitude response could be rising or falling)

So there's a lot of terminolgy and a lot of fundamentals to learn to
understand these things.
I think there's plenty of reading noted here to be getting on with if
you want to understand the subject

Cheers

PeteS

 

[Padu]

Does anyone know if using the lowest power consuming epia is possible?
can it run off generic batteries? are there alternatives to epia that
could use even lower power and run off generic batteries?

Any ideas?

I don't know about lowest power consuming, but I'm running mine out of
regular RC batteries wired in series. The batteries give me something around
12.5V. It is connected to a voltage regulator that regulates at 12V that is
connected to an ATX DC-DC board, that will condition the raw 12VDC to all
voltages that the epia (or any other PC for that matter) requires.

 

[Watson A.Name - \"Watt Su]

"Chris" <cfoley1064@yahoo.com> wrote in message
news:1116715409.256914.69340@f14g2000cwb.googlegroups.com...

[snip]

* A transistor will typically require much less power to operate than
a relay coil, especially if you use a darlington transistor or a
MOSFET.

A Darlington transistor requires a V drop of twice that of the single
junction transistor. The C-E V drop of a single junction can be a tenth
of a volt, but a darlington has to be at least 2 diode drops or about
1.2V to function. So the power wasted by a darlington is much greater
than with a single junction transistor.

If you want to minimize this, use a regular power transistor, and drive
it with another transistor connected common collector or emitter
follower. This basically means do _not_ connect the collectors together
in a darlington config.

Good luck
Chris

 

[Michael A. Terrell]

upgrdman@mindspring.com wrote:

Thanks all! I guess I will go with the RTV silicone stuff. My only
other question is if the silicone will effect the light output... my
LED's project their light in about a 60degree angle, and I wonder if
the silicone stuff will refocus the light?

What would be the best way to apply the stuff... just at the base of
the LEDs, or totally cover the LEDs in a think layer of the RTV silicon
stuff?

Lastly, since this will be on my RC car, dirt and other stuff will soon
cover parts of my stuff. I use the general parts-cleaners that
mechanics etc. use... spray can. Will that eat away at the RTV silicone
stuff, or cause harm to the resistors and LED's? Would just using soapy
warm water be better...and just let it dry thoroughly overnight?

Thanks again,
--Farrell F.

Be careful with RTV. There are two types and one corrodes wire. It
is marked, Not for electronic use.

--
Former professional electron wrangler.

Michael A. Terrell
Central Florida

 

[Michael A. Terrell]

Michael Black wrote:

(upgrdman@mindspring.com) writes:
I'm building some LED headlights for my radio-controlled car, and I
plan to use one of those project boards or whatever they're are called
to wire my LEDs and their resistors. But my RC car is gas powered, and
the engine puts out a lot of vibration. I'm concerned that my big white
LED's will be tugging a little on their solder joints without some sort
of brace, and I would like to just use some hot-glue form a glue gun.

But I'm new to electronics, and I do not know if the glue would be too
hot? and I doubt it, but does the glue conduct electricity?

Thanks,
--Farrell F.


I'd say it's safe, if your question is about whether the glue
will hurt the components.

But my experience with hot glue is that it tends to be less permanent,
ie it gets too warm or too old and things fall apart. At least,
with plastics.

Epoxy, or as someone said RTV silicone whatever, tends to be
more permanent. The latter, which can be a real drag to remove
if you need to, has the advantage that there's a level of flexibility
to cushion those vibrations.

Michael

I see a lot of LEDs mounted in consumer electronics with a little dab
of hot melt glue.

--
Former professional electron wrangler.

Michael A. Terrell
Central Florida

 

[Larry Brasfield]

"Watson A.Name - "Watt Sun, the Dark Remover""
<NOSPAM@dslextreme.com> wrote in message
news:119ku58s8vrkof9@corp.supernews.com...

"Chris" <cfoley1064@yahoo.com> wrote in message
news:1116715409.256914.69340@f14g2000cwb.googlegroups.com...
* A transistor will typically require much less power to operate than
a relay coil, especially if you use a darlington transistor or a
MOSFET.

A Darlington transistor requires a V drop of twice that of the single
junction transistor.

That is not a useful statement of the facts.

The C-E V drop of a single junction can be a tenth of a volt,

True (assuming you mean a single BJT). Or it can be more,
or less. A BJT in hard saturation can have 50 mV C-E drop.

but a darlington has to be at least 2 diode drops or about
1.2V to function.

Actually, the input BJT can and often does saturate to the
kind of drop stated above. It keeps the output BJT out
of saturation since the input C-E drop is in series with the
base of the output BJT. This results in typical darlington
C-E drops of 0.8 to 1.0 V. There is nothing about this
situation that makes "2 diode drops" significant.

So the power wasted by a darlington is much greater
than with a single junction transistor.

Assuming you mean a single bipolar junction transistor,
the truth of your claim depends largely on what supply
the base current is taken from. Where the input BJT
forced Beta is X, then for a bias supply greater than
X times the additional drop of darlington, your claim
is strictly false, (meaning "much greater" is no greater).

If you want to minimize this, use a regular power transistor, and drive
it with another transistor connected common collector or emitter
follower. This basically means do _not_ connect the collectors together
in a darlington config.

That may be a good strategy if a low voltage bias
supply is used and if the extra parts count is worth
the power savings. But the OP should be aware
that Darlington transistors have been used in many
places by people familiar with the alternatives.

These days, stringing together BJTs as you suggest
is rare. If the output drop is important, a single
MOSFET is generally favored.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[colin]

"davidd31415" <davidd31415@yahoo.com> wrote in message
news:1117403716.350815.95710@g43g2000cwa.googlegroups.com...

I'm looking for a way to measure a small change in resistance (not
necessarily a small resistance, just a small change). Is there a
common configuration of a wheatstone bridge or some other circuit that
I should consider for this? It is not a problem if the measurement
ends up being a voltage which needs to be converted to a resistance or
something similar.

I'm looking at measuring less then 1 ohm changes in 2-4kohm
resistances.

sounds just like a strain guage, you could use the same ciruit for one,
should be many examples from google.

Colin =^.^=

 

[mike]

casioculture@gmail.com wrote:

I'm wishing to make a DIY subnotebook, if possible.

Management summary: Forget it.

It'd use generic batteries,
What's a generic battery AA? D? car battery?
a monochrome display,
How are you gonna interface it?
a laptop keyboard,
Laptop keyboards don't plug into generic ps/2 connections.

a

flashcard reader,
You'll have to jump thru some hoops to make sure the flash is read only

and the system runs entirely out of ram. I'm not saying it can't be
done, just that someone has to do it.

and that's about it. I'll perhaps sculpt a case for

it, out of wood or similar material, with a dremel, if needed.

No harddrive, no floppy, no cd/dvd drive, no nonsense.

I just want to use a small linux distribution, and use it mostly to
edit text.

If you want to edit text, buy a laptop. Here in the US at garage sales
you can buy a laptop perfectly capable to edit text for a buck.
Old Compaq Aero 4/25 or 4/33C has a claimed battery life of six
hours...although I've never had the patience to run mine for that long.
But one of those will set you back almost ten bucks.
There are a bunch of palmtop computers with keyboards, but you'd
probably want an external one for serious typing. HP Jornada 690
was an interesting one with wide display.

I want it to have a long battery life, measurable in tens of

hours at least.
That's a stretch without some external battery. Radio Shack TRS-80

Model 100 claimed to have 20 hour battery life. And it edits
text...until you run out of memory ;-)

I googled epia. Lots of mention of low power, but the only sites that
published numbers used 120W to 200W power supplies. 200W x 20 hours is
only 4KWH of batteries to pack around.

So, if you're just looking for a woodworking project using a epia, go
for it.
If all you want to do is edit text, there are simpler, cheaper ways.
mike


I also want it to be inexpensive.
Well, a buck is pretty inexpensive.

Does anyone know if using the lowest power consuming epia is possible?
can it run off generic batteries? are there alternatives to epia that
could use even lower power and run off generic batteries?

Any ideas?

thanks

--
Return address is VALID but some sites block emails
with links. Delete this sig when replying.
..
Wanted, PCMCIA SCSI Card for HP m820 CDRW.
FS 500MHz Tek DSOscilloscope TDS540 Make Offer
Wanted 12" LCD for Compaq Armada 7770MT.
Bunch of stuff For Sale and Wanted at the link below.
MAKE THE OBVIOUS CHANGES TO THE LINK
ht<removethis>tp://www.geocities.com/SiliconValley/Monitor/4710/

 

[Conor]

In article <1117418019.302321.166390@g14g2000cwa.googlegroups.com>,
says...

I'm wishing to make a DIY subnotebook, if possible.

It'd use generic batteries, a monochrome display, a laptop keyboard, a
flashcard reader, and that's about it. I'll perhaps sculpt a case for
it, out of wood or similar material, with a dremel, if needed.

No harddrive, no floppy, no cd/dvd drive, no nonsense.

I just want to use a small linux distribution, and use it mostly to
edit text. I want it to have a long battery life, measurable in tens of
hours at least. I also want it to be inexpensive.

Does anyone know if using the lowest power consuming epia is possible?
can it run off generic batteries? are there alternatives to epia that
could use even lower power and run off generic batteries?

Any ideas?

Buy an old 486 off E-Bay for Ł30.

--
Conor


"Be incomprehensible. If they can't understand, they can't disagree"

 

[mlw]

casioculture@gmail.com wrote:

I'm wishing to make a DIY subnotebook, if possible.

It'd use generic batteries, a monochrome display, a laptop keyboard, a
flashcard reader, and that's about it. I'll perhaps sculpt a case for
it, out of wood or similar material, with a dremel, if needed.

No harddrive, no floppy, no cd/dvd drive, no nonsense.

I just want to use a small linux distribution, and use it mostly to
edit text. I want it to have a long battery life, measurable in tens of
hours at least. I also want it to be inexpensive.

Does anyone know if using the lowest power consuming epia is possible?
can it run off generic batteries? are there alternatives to epia that
could use even lower power and run off generic batteries?

Any ideas?

The fan-less EPIA mother boards seem to use the least power.
The highest power density consumer batteries are the rechargable NiMH AA
batteries. You can get NiMH R/C battery packs, they are more expensive and
resist the "memory" effects of NiCAD.

 

[Don Klipstein]

In <1117030825.655422.27840@f14g2000cwb.googlegroups.com>, PeteS wrote:

Fibrillation (which is what kills you) is perfectly possible with a 12V
battery in the 'right' conditions.

What it takes is 100mA through the heart (an acquaintance of mine got
killed this way doing a charging check on the 28VDC system in a
helicopter many years ago)

Most references say fibrillation is generally a problem at 100 mA to an
amp, with one or two saying this starts at 50 mA.

I do not believe the risk of fibrillation drops to zero when the current
decreases to 99 or 49 mA. I have heard of someone getting killed by a 30
mA neon sign transformer.

As for 12 volts being enough to push enough current through you to cause
electrocution? Not impossible, but very rare - requiring broken skin
or large skin contact area with wet skin.

I think a greater hazard is shorts causing those burning hot wedding
rings, also burning wires causing fires, and burning wires or sparks (and
flying droplets of molten metal from sparks) igniting explosive gases that
lead acid batteries sometimes produce.

Other hazards to watch out for: Ignition voltage - usually not lethal,
but I don't feel certain. Also shocks could jolt you into dropping a
wrench onto a +12V point and a ground point, or getting
fingers/hands/clothing caught in moving fans or belts.

- Don Klipstein (don@misty.com)

 

[Don Klipstein]

In article <1117410333.066350.174860@g44g2000cwa.googlegroups.com>, Bill
Bowden wrote:

120 or 240 is not very high. You would get shocked, but probably
wouldn't die.

What news source are you reading? People are electrocuted
every year from those "not very high" voltages.

I'm not reading a news source, just stating experience.
I've been shocked many times from line voltages with
no ill effects. Once, I was shocked by 10KV from
an aviation radar system, and it threw me across the room,
but I got up and went back to work.

120VAC is low voltage. Why do you think it's used instead
of 880 or higher, which would be much more efficient?

One problem with 120V is its perceived safety. People get more
careless, and as a result despite a small percentage of shocks from that
voltage being fatal, that voltage has a high body count.

US Navy warships have most of their power circuits being 440V, and most
of their electrocution deaths from the 110V that also exists there.

- Don Klipstein (don@misty.com)

 

[John Popelish]

Don Klipstein wrote:
(snip)

I do not believe the risk of fibrillation drops to zero when the current
decreases to 99 or 49 mA. I have heard of someone getting killed by a 30
mA neon sign transformer.
(snip)

Which puts out about twice that on into a low impedance load, like the
human body.

 

[John Fields]

On Mon, 30 May 2005 17:21:37 -0400, John Popelish <jpopelish@rica.net>
wrote:

Don Klipstein wrote:
(snip)
I do not believe the risk of fibrillation drops to zero when the current
decreases to 99 or 49 mA. I have heard of someone getting killed by a 30
mA neon sign transformer.
(snip)

Which puts out about twice that on into a low impedance load, like the
human body.

---
It can't, since it's designed to saturate at 30mA, but looking at its
load line it'll put out, say, 15kV at 0A into an open, and 0V at 30mA
into a dead short.

That means that with an initial 500kohm human load across it its
output voltage will drop to 7500VRMS and it'll be forcing 15mA through
the load, and the load will be dissipating about 113 watts. OUCH!!!

--
John Fields
Professional Circuit Designer

 

[John Popelish]

John Fields wrote:

On Mon, 30 May 2005 17:21:37 -0400, John Popelish <jpopelish@rica.net
wrote:


Don Klipstein wrote:
(snip)

I do not believe the risk of fibrillation drops to zero when the current
decreases to 99 or 49 mA. I have heard of someone getting killed by a 30
mA neon sign transformer.

(snip)

Which puts out about twice that on into a low impedance load, like the
human body.


---
It can't, since it's designed to saturate at 30mA, but looking at its
load line it'll put out, say, 15kV at 0A into an open, and 0V at 30mA
into a dead short.

That means that with an initial 500kohm human load across it its
output voltage will drop to 7500VRMS and it'll be forcing 15mA through
the load, and the load will be dissipating about 113 watts. OUCH!!!

You may be right, but that is not what I understand to be the case. I
thought they are rated for normal load current over the voltage range
expected when driving a gas tube. And that they have a very nonlinear
current limit, much like Sola ferro resonant constant voltage
transformers. Those hold specified voltage regulation at rated
current but the current increases only to about double rated under a
short circuit. I don't think most neon sign transformers are just a
tightly coupled step up transformer in series with a big resistor.

 

[Dorothy Bradbury]

I'm wishing to make a DIY subnotebook, if possible.

You are going to run into a few problems here...

Do a requirements specification
o What functionality do you require
---- whiteboard 3 levels -- ideal (dream on), realistic, minimum
o What do you have to spend
---- whiteboard 3 levels -- worst, best, middle
o What is the likely basic component cost
---- whiteboard 3 levels -- worst, best, middle
---- include R&D -- prototyping defines over-budget

Do a feasibility study.
o Display -- your biggest problem
---- TTL desktop -- smallest is MOBI 15", 2kg, conventional 3.8kg+
---- LVDS laptop -- requires LVDS EPIA m/b, Ł199 for 15", 1kg
o Display mounting -- friction hinges
---- RS do a small & a large - Ł8 small, Ł14 large
--------- if you need these, let me know I have some new
---- NO friction hinge will hold a desktop TFT at its edge
--------- rotational moment is huge re 1/2-ht * weight
o Keyboard type -- small & lightweight
---- Cherry G84 with Trackball
---- IBM Travel Keyboard with Trackpad & Trackpoint
---- both are 22mm high, compact
o Battery -- LI-Ion possible, also Lead Acid
---- weight vs power draw is an issue
o Vibration/Shock -- basic knockable
---- this gets ugly on cost, complexity, capability
o Packaging -- your biggest problem
---- custom - alloy angle, honeycomb PP, latches, corners, edging - 10lb
-------- customisable but design LAST re internal space
---- Pelican case - flange mount case for keyboard, TFT in lid - 10lb
-------- gives you a sealed box, use flying cables to panel mount skts

Components exist to make it work - at a price.
Problem in reality is the weight - it adds up very fast.

Whatever you do, you have a chain of dependencies...
o Keep the design open as long as possible
---- packaging should be the last thing
---- making it fit a package can be making a rod for your own back
o Identify those dependencies re Change-A = Change-B-C-D
---- eg, TFT size/type changes case size, m/b spec, layout
---- eg, PSU size/type changes case size, PC spec
o Identify those areas which COULD change in future
---- eg, battery/PSU tech changes requiring different form factor
---- so create a degree of contingency in the design for such
---- common for a design to be obsolete before it is in use
o Identify each option at each stage
---- whiteboard the various options of doing *anything*
---- keep a record, and go back over it

Pilot on paper or ideally 2D CAD package - plenty of cheap ones.

The problems are...
o You want a sub-notebook -- packaging problem
---- custom cases are limited by extrusions for edges & top/bottom
-------- ex - Z-edging is 22-27mm, corner-edging is 22-27mm
------------ that means 44-54mm for EACH of top & bottom = 88-108mm
------------ you have form-factor height on cooling fan & connectors
---- off the shelf cases are limited in range & similarly sizing
-------- ex - Pelican 1470 is slim, but what can you fit in it
------------ you still have form-factor height on cooling fan & connectors
o You want a screen hinging down over a keyboard
---- that requires something to a) limit the angle b) provide adjustment
---- which is known as a friction hinge, which Pelican don't offer
---- laptop TFTs are super-light, extra-thin (0.9mm glass), limited bracing

Key problem often ignored - look at your laptop, the keyboard sits in a
pool of material which doesn't impinge on the wrists. Either a Pelican case
or flight case solution will have a Z-edging or U-edging which will press
against the wrists, and be very uncomfortable. Ok, so you could stick a
gel pad in the way to provide cushioning, the lid then clamshells down.


There is a product which does exactly what you want...
o Around 27% of the rugged market is still 1.4-2.7B$ these days
---- it isn't laptops (Toughbook, Dolch briefcase jobbie)
---- it is Luggables - Lunchbox PCs
o You could realistically create a Luggable
---- PC + TFT in a box, lid comes off, floating standard or slim keyboard

The only way you can realistically create a sub-notebook is...
o Tiny 10.4"-TFT LVDS display in the lid of a case
o IBM Travelsaver or Cherry G84 super-light super-slim 22mm keyboard
o VIA C3 in ideally non-fan version (533Mhz) or AMD Geode etc
---- Mini-ITX or EBC or SBC -- www.bvm-store.com for ideas
---- ensuring you get a LVDS version, and cable & bits n bobs
o DC-2-DC convertor board re ATX - or - a m/b with onboard convertor
---- some boards have 1 voltage input, eg, Mobile Celeron needs 5V etc
o Battery -- price is key here
---- big $ -- LI-Ion generic & charger - someone on uk.adverts.computer
---- small $ -- lead acid gel type - deep cycle discharge type, quite heavy

You are still going to find it heavy due to the casing:
o Flight case
---- parts -- www.penn-fabrication.com
-------- they do the h/w you need from latches to Z-edging & angle
-------- you will want to use 5mm sheet section stuff re weight
---- case sheeting -- forget ply, you want a) honeycomb or b) PP
-------- solid PP sheet from bayplastics, still heavy, leathergrain (PC monitor)
-------- honeycomb PP does exist in 5mm, most commonly 7mm (Astroboard)
o Pelican case
---- even small ones are still the same 1/4"-PP which has weight
---- it's going to be about 5-6lbs for small but usable

More likely you create a luggable...
o Any size TFT monitor - lightweight MOBI 15" or standard desktop 15"
---- use the VESA mount on the latter, creativity on the former (MOBI)
---- the MOBI is actually a laptop panel with LVDS input
---- you need a TFT with 12V input (external power brick), power off PC PSU
---- realise a desktop TFT = 30W due to backlight = ~2.5-3A at 12V
o IBM / Cherry keyboard
o 1U PSU or DC-2-DC convertor etc
o Motherboard from super-low power Geode to Dual Xeon
o Battery or very long mains lead
o Build PC, stick TFT to PC, stick whole lot in the flight case
---- ideally on rubber stud mounts -- www.rswww.com
---- eg, Paulstra Diabolo, Radiaflex, gives a bit of shock mounting
---- shock mounts must only be in compression/shear, not tension
o Fit keyboard by velcro retainer belt into the front lift-off-lid
o Fit 4 feet, use panel mount connectors on the flight case
---- or go cheap and have m/b connectors thro to the case side

Astronomers to Tropical Forest researchers have used various forms.
One wanted a Peli 1610 (big such that council tax is payable) with a very
low power CPU, huge SLA for ease of replacement, lots of 2.5" disks. It
was used for radio telemetry logging in some place they didn't want him
back from, ever, like they didn't even offer a map for him to even find it.

So it comes down to is it practical - or economic - for what you want.

If you want a customisable laptop, stripped down, try Asus.
If you want a rugged low power laptop, try a CF-27 ToughBook.

Whiteboard (even on paper) all the ideas, possibilities - don't discount any
at first as they often give insight into other solutions (or where they fail).

I use a luggable server...
o I needed -- Rugged + Multi-PCI slots + Easily Repaired + Upgradeable LT
---- basically I have a laptop, but needed a very flexible server
---- able to take anything, be shipped, wheeled, yet very cheap
---- no external connectors physically linked to internal re damage
o Chassis cost ~Ł180, sub 18lb, stainless, alloy & PP
---- takes 17" or 15" VESA mount TFT (not that you could tell)
---- integral wheels, shock mounted to about 3ft (shake table tested)
---- takes off the shelf PC parts, beats Ł4-8k luggables
---- Bulgin panel mount RJ45 to USB & cable link to m/b

It was however a pilot for a commercial unit for video production people,
and one currently having the daylights beaten out of it around Brazil. Asset
is 1) power 2) ruggedness 3) commodity upgradeable 4) super low cost.

So define what you need carefully.
You will struggle to get a sub-notebook size solution of similar fnality.

You can even recycle a notebook - but TFTs are tied to onboard graphics,
and there are a couple of variations of LVDS (making laptop TFT re-use hard).

Biggest problem is laptop size = custom enclosure = custom wallet.

Separating the TFT from computer makes life easier:
o Easy to create/buy a micro-PC - EBC, SBC board or full Micro-PCs
o Then take a TTL TFT - 8", 10.4" mini-monitors exist quite cheaply
o Stick the two in a simple flight case or nylon camera case etc

If you run an EPIA off a 12V SLA...
o Really you need a car-battery DC-2-DC convertor
o This monitors the voltage re protecting the battery
o Do a google for Mini-ITX - Car PCs & Embedded Alarm/X10 apps

Have fun
--
Dorothy Bradbury
www.dorothybradbury.co.uk for NMB & Panaflo (MMM) fans, free shipping

 

[John Popelish]

smokie wrote:

wouls a sinusoidal input to a comparator produce the same transfer
curve as a triangle waveform

The transfer function is the same but the output may not be exactly
the same.

If the amplitudes and frequencies of the sine and triangle are the
same, the sine has twice the rate of change of voltage at the zero
crossings, compared to the triangle wave, so the comparator passes
through the linear gain input range twice as fast for the sine wave.
Of course the linear input range is very small, so the difference may
not be noticeable unless you make very careful measurements, or the
frequency is very low.