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AREF bypass capacitance on ATMega2560?

J

Joerg

Jan 1, 1970
0
Joerg wrote:
[email protected] wrote:
[email protected] wrote:
[...]

... Design to 85C isn't just a good idea, it's the
spec (-40C to 85C).
It is a bad spec. The result of such flawed design evidences itself over
and over. For example, the minivan of friends of ours would not start
when parked at a mall on a hot day after more than 15mins of driving. It
would (sometimes) come back to life if you let it sit for half an hour
so the radiated engine heat became less. In the winter it was mostly ok.
That design is IMHO junk.
Oh, the spec I mentioned above isn't for the engine compartment or any
of the ignition or safety gadgets. It's for the noise makers. ;-)
yes, that's the unpowered temperature. Temp rise has to be added to
that.

Ok, if the radio quits on a hot day that isn't going to cause much
grief. Happened to me but luckily within the warranty period. It's
annoying though, leaves kind of a cheap feeling about the whole car even
though the car doesn't deserve that. Radios are usually in the dash and
that can exceed 80C on hot days. Then the driver hops into the car,
turns on the stereo, pops in the Eric Clapton CD, listens to "Cocaine"
with the volume on 10 and ... *PHUT* ... :)

Question: What do you do with an FPGA in a radio?
Lotsa possibilities. So far very few real applications; too
expensive. ...

I look at radio and other consumer gear a lot, mainly to spot
interesting ICs and other parts that I might be able to use on my
designs. Never seen an FPGA in there, ever.

They're not common yet but they will find their way in. Again, cost
is the biggest barrier. OTOH, function will eventually demand them.
I know, dad's Blaupunkts were better :-(

Hardly. Dad never had a 17" LCD display on his and the XM reception
sucked. ;-)

Those things aren't important to me. What is importnat to me is large
signal handling. For example, the new radios fall apart on the Bass Lake
Grade on Hwy 50 because there are all the TV towers for the valley. The
Blaupunkt doesn't fall apart.

You want to listen to AM/FM radio stations? What kind of nut are you,
anyway? ;-)


I actually still listen to AM a lot. Oh, and I do not have a smart phone :)
 
P

Paul

Jan 1, 1970
0
Cell phones are short-lived products. One year, if that. Med/aero is a
whole different set of metrics. We need to rely on parts still being
there 10, 20 or more years doen the road.

Around 2002 to 2004 I had an enquiry to look at improving an NMR system
at a hospital. When I asked them what the age of the machine was they
said -

"The earliest record we have is when it MOVED to the new building
in 1968"


--
Paul Carpenter | [email protected]
<http://www.pcserviceselectronics.co.uk/> PC Services
<http://www.pcserviceselectronics.co.uk/pi/> Raspberry Pi Add-ons
<http://www.pcserviceselectronics.co.uk/fonts/> Timing Diagram Font
<http://www.gnuh8.org.uk/> GNU H8 - compiler & Renesas H8/H8S/H8 Tiny
<http://www.badweb.org.uk/> For those web sites you hate
 
T

Tim Williams

Jan 1, 1970
0
Paul said:
Around 2002 to 2004 I had an enquiry to look at improving an NMR system
at a hospital. When I asked them what the age of the machine was they
said -

"The earliest record we have is when it MOVED to the new building
in 1968"

Geez, was it a frequency-sweep unit? LOL

Tim
 
J

Joerg

Jan 1, 1970
0
Paul said:
Around 2002 to 2004 I had an enquiry to look at improving an NMR system
at a hospital. When I asked them what the age of the machine was they
said -

"The earliest record we have is when it MOVED to the new building
in 1968"

Some stuff lasts a long time. Here is Betsy, we used her to split firewood:

http://www.analogconsultants.com/ng/images/splitter.JPG

1942 surplus army motor, all mounted on the front axle of a 1939 DeSoto.
You can still get the tires.
 
P

Piotr Wyderski

Jan 1, 1970
0
rickman said:
That is the sort of thinking that is just a pair of blinders. I don't
care if the real estate is "expensive". I care about my system cost.
Gates in an FPGA are very *inexpensive*. If I want to use them for a
soft core CPU that is just as good a use as a USB or SPI interface.

As long as the softcore is just a supplement to the really complex
logic. Otherwise it is not the best way to use the FPGA resources
in order to emulate an ARM. There already are dirt-cheap ARMs on
the market. I've done just a single hobby project based on FPGA
(and think about the next one), but it works and my experience is
as follows. Pros:

1. You can solder the chip and *then* start thinking what
actually it should do. :)

2. The PCB routing in case of not very demanding signals
is so easy...

3. There is no problem with resource conflicts. When I want
an ARM with 6 UARTS, there are not many of them and then...
look... I can't use CAN becase it reuses the pins of one
of the UARTs... remap... damn, now the Ethernet MII bus
collides with that. On an FPGA I can have 134 UARTS if
I want and no pin collisions.

4. There is simply no competition for FPGAs when precise
timing is required. It is just so indecently easy. Doing
something as "complex" as 40 PWM channels (which is what
I need now) on an MCU is a nightmare.

Cons:

1. You can simulate basically anything, but most of the
time there is no need for that. Some functional blocks
have the only sacred specification and you better not
"improve" them. Memory controllers, serial protocol
controllers, the CPU.

2. Why on Earth is there something as bizarre as NIOS
or *blaze? We don't need the next invention of a wheel.
The world pretty much converged to the ARM architecture,
so I do not want to waste my time on learning about
a niche design just because it is the only thing I can
have there because it doesn't exceed the resources
available (opencores) or because of legal issues. I do
want an ARM in every Spartan-class FPGA. I am not going
to buy a Virtex just for that purpose.

3. No analog stuff. Everything interesting needs to
be external. Welcome back to the 80s... :-/

4. Supply voltage issues. Do we really need 3 of them?

5. Why does it take so long to recompile the design?

6. Using a ready-made MCU at least the core has been debugged.
Do I really need to debug the processor in addition to debugging
its program?

Best regards, Piotr
 
P

Piotr Wyderski

Jan 1, 1970
0
Joerg said:
Question: What do you do with an FPGA in a radio?

As a matter of fact, it is one of the best places to use an FPGA. :)
SDR with FPGA reconfiguration capabilities is the ideal solution.
Not for a regular FM noisemaker, though...

Best regards, Piotr

*) It was exactly the only time in my life when I used an FPGA.
+ a 14-bit@65MHz Analog Devices ADC + 104 MHz DAC.
 
J

Joerg

Jan 1, 1970
0
[email protected] wrote:
Joerg wrote:
[email protected] wrote:
[email protected] wrote:
[...]

... Design to 85C isn't just a good idea, it's the
spec (-40C to 85C).
It is a bad spec. The result of such flawed design evidences itself over
and over. For example, the minivan of friends of ours would not start
when parked at a mall on a hot day after more than 15mins of driving. It
would (sometimes) come back to life if you let it sit for half an hour
so the radiated engine heat became less. In the winter it was mostly ok.
That design is IMHO junk.
Oh, the spec I mentioned above isn't for the engine compartment or any
of the ignition or safety gadgets. It's for the noise makers. ;-)
yes, that's the unpowered temperature. Temp rise has to be added to
that.

Ok, if the radio quits on a hot day that isn't going to cause much
grief. Happened to me but luckily within the warranty period. It's
annoying though, leaves kind of a cheap feeling about the whole car even
though the car doesn't deserve that. Radios are usually in the dash and
that can exceed 80C on hot days. Then the driver hops into the car,
turns on the stereo, pops in the Eric Clapton CD, listens to "Cocaine"
with the volume on 10 and ... *PHUT* ... :)

Question: What do you do with an FPGA in a radio?
Lotsa possibilities. So far very few real applications; too
expensive. ...
I look at radio and other consumer gear a lot, mainly to spot
interesting ICs and other parts that I might be able to use on my
designs. Never seen an FPGA in there, ever.
They're not common yet but they will find their way in. Again, cost
is the biggest barrier. OTOH, function will eventually demand them.

... These are not your father's Blaupunkts. ;-)
I know, dad's Blaupunkts were better :-(
Hardly. Dad never had a 17" LCD display on his and the XM reception
sucked. ;-)
Those things aren't important to me. What is importnat to me is large
signal handling. For example, the new radios fall apart on the Bass Lake
Grade on Hwy 50 because there are all the TV towers for the valley. The
Blaupunkt doesn't fall apart.

The reality is that these things are important to the vast majority of
consumers, therefore customers. Your wishes don't make a significant
market.

Vast majority = GUM :)

What matters is a sticker with very high PMPO number on there and lots
of blue LEDs.

Since new radios are mostly junk I haven't bought one in over 20 years
except a new living room stereo. And only because SWMBO kept complaining
that the old (well running ...) Kenwood tower was too large and "ugly".
Boy did I regret that, the new stereo is completely useless on the AM band.

So do I, actually, but also XM, now (very little FM - decent reception
area is too small to bother). I also use an MP3 player and I'd like
to pipe my smart phone's navi through it, but it's broken (designed
broken by Microsoft).


I have yet to migrate into that sort of gear. Didn't have a need yet.
 
J

Joerg

Jan 1, 1970
0
Piotr said:
As a matter of fact, it is one of the best places to use an FPGA. :)
SDR with FPGA reconfiguration capabilities is the ideal solution.
Not for a regular FM noisemaker, though...

Best regards, Piotr

*) It was exactly the only time in my life when I used an FPGA.
+ a 14-bit@65MHz Analog Devices ADC + 104 MHz DAC.

It's going to be a tough sell for a radio. Even if they found one for $3
that's too much and they also can't stomach the 10sec to download the
compiled data in production.

Everything has to fit into the $149.95 sale price at the auto parts
place, with fat profit margins for everyone and their middlemen,
speakers, wires, neon-colored huge window sticker, a discount coupon for
installation, free coffee and free waffles :)
 
P

Piotr Wyderski

Jan 1, 1970
0
Joerg said:
It's going to be a tough sell for a radio.

A car radio? Well, there's nothing to reconfigure, maybe
except of the station. :) It had to be a homebrew wideband
every-conceivable-modulation-capable scanner. It works to
some extent at the hardware level but I've kind of lost my
interest in SDR to finish the software side. Read: got married. ;-)

Best regards, Piotr
 
T

Tauno Voipio

Jan 1, 1970
0
A car radio? Well, there's nothing to reconfigure, maybe
except of the station. :) It had to be a homebrew wideband
every-conceivable-modulation-capable scanner. It works to
some extent at the hardware level but I've kind of lost my
interest in SDR to finish the software side. Read: got married. ;-)

Best regards, Piotr

That's the right attitude: Forget radio, you have better things to do.
 
J

Joerg

Jan 1, 1970
0
Piotr said:
A car radio? Well, there's nothing to reconfigure, maybe
except of the station. :)


But wait, there's more. Blue blinkenlights, yellow blinkenlights. When
we rented a Mustang I thought I'd stepped into a disco.

... It had to be a homebrew wideband
every-conceivable-modulation-capable scanner. It works to
some extent at the hardware level but I've kind of lost my
interest in SDR to finish the software side. Read: got married. ;-)

Oh. You, too? :)

My ham radio days are more or less over for the same reason but maybe
I'll pick it up again when I gradually retire. Some day. But first I
want to get back into beer brewing.

I never had much fun with SDR because it's expensive and generally
inferior to the classic circuits when it comes to performance. I do now
have one spectrum analyzer (the Signalhound) that is basically an SDR.
But that is because I need it for my job, not for fun.
 
J

Joerg

Jan 1, 1970
0
Tauno said:
That's the right attitude: Forget radio, you have better things to do.

But those have serious financial consequences down the road. Diapers,
braces, tuition costs, driver license, higher car insurance premiums,
the family car wrapped around a power pole, car insurance going up some
more because of that, and so on.
 
T

Tauno Voipio

Jan 1, 1970
0
But those have serious financial consequences down the road. Diapers,
braces, tuition costs, driver license, higher car insurance premiums,
the family car wrapped around a power pole, car insurance going up some
more because of that, and so on.

Yep - but that's a blunder everybody has to do self.
 
R

rickman

Jan 1, 1970
0
It's going to be a tough sell for a radio. Even if they found one for $3
that's too much and they also can't stomach the 10sec to download the
compiled data in production.

You really have no interest in learning anything about FPGAs that has
happened in the last 10 or 15 years do you?

Everything has to fit into the $149.95 sale price at the auto parts
place, with fat profit margins for everyone and their middlemen,
speakers, wires, neon-colored huge window sticker, a discount coupon for
installation, free coffee and free waffles :)

You two are talking about totally different radios.
 
T

Tauno Voipio

Jan 1, 1970
0
So according to that we'd both be results of blunders? :)

Yes - and winners, about 1 to a few hundreds of millions in the great
race of Nature.
 
J

Joerg

Jan 1, 1970
0
rickman said:
You really have no interest in learning anything about FPGAs that has
happened in the last 10 or 15 years do you?

Oh, I do. I just reviewed a design that has some rather fat ones in
there and it would hardly have been possible to do this without FPGA.
However, there are circuits where FPGAs are a perfect fit and others
where they just aren't. In ordinary radios they usually aren't.
You two are talking about totally different radios.

The last few posts were about car radios, because the topic was
electronics and temperature exposure in cars.
 
[email protected] wrote:
[email protected] wrote:
Joerg wrote:
[email protected] wrote:
[email protected] wrote:
[...]

... Design to 85C isn't just a good idea, it's the
spec (-40C to 85C).
It is a bad spec. The result of such flawed design evidences itself over
and over. For example, the minivan of friends of ours would not start
when parked at a mall on a hot day after more than 15mins of driving. It
would (sometimes) come back to life if you let it sit for half an hour
so the radiated engine heat became less. In the winter it was mostly ok.
That design is IMHO junk.
Oh, the spec I mentioned above isn't for the engine compartment or any
of the ignition or safety gadgets. It's for the noise makers. ;-)
yes, that's the unpowered temperature. Temp rise has to be added to
that.

Ok, if the radio quits on a hot day that isn't going to cause much
grief. Happened to me but luckily within the warranty period. It's
annoying though, leaves kind of a cheap feeling about the whole car even
though the car doesn't deserve that. Radios are usually in the dash and
that can exceed 80C on hot days. Then the driver hops into the car,
turns on the stereo, pops in the Eric Clapton CD, listens to "Cocaine"
with the volume on 10 and ... *PHUT* ... :)

Question: What do you do with an FPGA in a radio?
Lotsa possibilities. So far very few real applications; too
expensive. ...
I look at radio and other consumer gear a lot, mainly to spot
interesting ICs and other parts that I might be able to use on my
designs. Never seen an FPGA in there, ever.
They're not common yet but they will find their way in. Again, cost
is the biggest barrier. OTOH, function will eventually demand them.

... These are not your father's Blaupunkts. ;-)
I know, dad's Blaupunkts were better :-(
Hardly. Dad never had a 17" LCD display on his and the XM reception
sucked. ;-)

Those things aren't important to me. What is importnat to me is large
signal handling. For example, the new radios fall apart on the Bass Lake
Grade on Hwy 50 because there are all the TV towers for the valley. The
Blaupunkt doesn't fall apart.

The reality is that these things are important to the vast majority of
consumers, therefore customers. Your wishes don't make a significant
market.

Vast majority = GUM :)

What matters is a sticker with very high PMPO number on there and lots
of blue LEDs.

Blue LEDs are *so* last century. The 17" color LCD display is where
it's at.
Since new radios are mostly junk I haven't bought one in over 20 years
except a new living room stereo. And only because SWMBO kept complaining
that the old (well running ...) Kenwood tower was too large and "ugly".
Boy did I regret that, the new stereo is completely useless on the AM band.

Ours is likely 10Y). No reason to buy a new one, it's rarely used.
I have yet to migrate into that sort of gear. Didn't have a need yet.

You're just a stubborn old geezer. ;-)
 
But wait, there's more. Blue blinkenlights, yellow blinkenlights. When
we rented a Mustang I thought I'd stepped into a disco.

Our Mustang's instrument cluster can be color coordinated. It's
something to do while driving down the road, I suppose.
Oh. You, too? :)

My ham radio days are more or less over for the same reason but maybe
I'll pick it up again when I gradually retire. Some day. But first I
want to get back into beer brewing.

First things first!
I never had much fun with SDR because it's expensive and generally
inferior to the classic circuits when it comes to performance. I do now
have one spectrum analyzer (the Signalhound) that is basically an SDR.
But that is because I need it for my job, not for fun.

That's sorta the way I feel about the whole topic.
 
R

rickman

Jan 1, 1970
0
As long as the softcore is just a supplement to the really complex
logic. Otherwise it is not the best way to use the FPGA resources
in order to emulate an ARM. There already are dirt-cheap ARMs on
the market.

The issue is not the cost of an MCU. There are any number of reasons
why not to use a separate chip for the CPU. The one I encounter most
often is board space. In a design I did some years ago I barely had
room for the logic at all, but there was no way I would have been able
to squeeze in a separate MCU package. There is also the cost. Although
a $3 CPU seems cheap, if it can't do the entire job, you can likely
include a soft CPU on the FPGA and only have one part rather than two.

If an MCU does the entire job you need, then fine, use it. But there
are plenty of times you need both and you can always include a CPU on
your FPGA, but it is hard to make a CPU do what the FPGA does.

I've done just a single hobby project based on FPGA
(and think about the next one), but it works and my experience is
as follows. Pros:

1. You can solder the chip and *then* start thinking what
actually it should do. :)

That's not a good idea for either an MCU or an FPGA.

2. The PCB routing in case of not very demanding signals
is so easy...

There are plenty of dedicated I/Os on an FPGA. Clock lines are the most
obvious. Although you can bring a clock into the chip on any I/O pin,
if you don't use a clock pin it will have extra delay getting to the
clocked elements. This can cause timing issues on clocked I/Os.

3. There is no problem with resource conflicts. When I want
an ARM with 6 UARTS, there are not many of them and then...
look... I can't use CAN becase it reuses the pins of one
of the UARTs... remap... damn, now the Ethernet MII bus
collides with that. On an FPGA I can have 134 UARTS if
I want and no pin collisions.

The routing on an FPGA is one of it's claims to fame. It is also the
major source of the "inefficiency" and extra cost compared to dedicated
logic. But most of the time the "cost" of using an FPGA is mitigated by
Moore's law and the result of FPGAs often using newer and more efficient
fabrication processes.

4. There is simply no competition for FPGAs when precise
timing is required. It is just so indecently easy. Doing
something as "complex" as 40 PWM channels (which is what
I need now) on an MCU is a nightmare.

Yeah, I looked at using a 144 core MCU to control an SDRAM. Although
each MCU could run at up to 700 MIPS, the timing was not specified well
enough to big bang the I/Os for the SDRAM at any speed above some 25 MHz
(ball park).

Cons:

1. You can simulate basically anything, but most of the
time there is no need for that. Some functional blocks
have the only sacred specification and you better not
"improve" them. Memory controllers, serial protocol
controllers, the CPU.

I'm not sure what this means.

2. Why on Earth is there something as bizarre as NIOS
or *blaze? We don't need the next invention of a wheel.
The world pretty much converged to the ARM architecture,
so I do not want to waste my time on learning about
a niche design just because it is the only thing I can
have there because it doesn't exceed the resources
available (opencores) or because of legal issues. I do
want an ARM in every Spartan-class FPGA. I am not going
to buy a Virtex just for that purpose.

It is not possible to implement an ARM on an FPGA without paying huge
license fees. But no matter, what is magical about an ARM? No
instruction set owns the market. ARM has no real advantage over other
CPUs in an engineering sense. There is little utility to sticking with
one instruction set unless you program in assembly language. However,
if you have a large code base that is not easy to port to a different
processor, then stick with what you know.

3. No analog stuff. Everything interesting needs to
be external. Welcome back to the 80s... :-/

I suggest you look at the Microsemi Fusion and Smart Fusion devices.
Fusion means it has analog on chip and Smart Fusion means it has analog
plus an ARM CPU. I have not worked with it, so I don't know much about
it. It is also a bit pricey for the original conversation we had in
this thread.

4. Supply voltage issues. Do we really need 3 of them?

I don't know, do you? My current board has four power supply voltages
and an extra 3.3 volt on board for the CODEC (a total of 5 separate
rails) , but only one is for the FPGA. How about your designs?

5. Why does it take so long to recompile the design?

How long is a piece of string? What?

Are you talking about the place and route time? That depends on the
size of the chip and the speed of your processor (and amount of memory).
I tend to use smaller designs which compile fairly fast. But more
importantly that is not a real issue because I don't compile until the
design passes simulation and finding bugs usually takes a while longer
than the compile.

6. Using a ready-made MCU at least the core has been debugged.
Do I really need to debug the processor in addition to debugging
its program?

I don't know, do you? Which processor are you thinking of using? What
is the application? What are your requirements? BTW, have you read the
errata sheet for any MCU? They are typically very long with lots of
bugs they don't plan to fix. Pick a new member of the family and you
get to find the bugs!
 
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