Need small micro dev kit

The text below was part of an ongoing thread that I was participating
on another board. Some of the members on the other board asked exactly
what I was wishing to accomplish so the topic is treated in more detail
than most. I'm still looking for a small (INEXPENSIVE) kit

I want to develop an inverter to take a 200v dc bus and convert it to
120vac. I will use 4 mosfets configured in an H configuration. By
controlling the switching trajectory of each fet the output will be
sinusoidal in shape. Of course there will be some switching garbage in
the
way of harmonics that I will have to deal with. A mosfet will allow a
carrier switching rate of say 20kHz no problem - the faster you switch
the
higher will be the spectrum of harmonic trash that needs to be
filtered. So
then the faster you switch the easier the filter design becomes. A
switching
rate that is an exact multiple of 60Hz would be good so that the
carrier and
the fundamental components can be synchronized - called synchronous
pwm.
This may be easier to implement with a small micro.

The 200v dc bus will probably come from 4 car batteries connected in
series.
This will go into a full bridge phase shift converter running at 100kHz
or
so - I've got a couple kicking around here that I have already built.
The
200v bus can be regulated to within a gnat's ass, so the sinewave
inverter
can run open loop without having to compensate for bus voltage
variations.

So what the micro has to do is output the pwm routine to drive the 4
mosfets. This could be as simple as a counter and a table with the pwm
times stored. Go to address 1 and load that number into the
counters(and
the info for state latch as well). Count down to zero and go to address
2
and load that number into the counters. Perhaps there are 200 (for a
12kHz
carrier) address that store the timing and state information for one
sinewave.

There are only 4 possible states with the inverter while it is
running.. Top
right and bottom left both on. Top left and bottom right both on. Both
top
on, or both bottom on - each called a zero state. Only other possible
state
is all fets off, but that is never used while the inverter is running.
Never are the top and bottom transistors in the same pole on, because
that
would put a direct short across the bus.

My microprocessor skills are almost non-existant so I am looking to
getting
my feet wet. Whatever platform I choose (based on you guy's input) it
should be above everything else easy to learn. It must also have the
computing power necessary to do the pwm routine. I'm basically looking
for
somebody to tell me to go to digikey and order such and such a kit.

thanks
Bob

 

Hmmmmm.....
sounds like a DarwinAwards project, go for it...

martin

 

To ensure accurate timing it's best to 'flip' each state change with an
interrupt driven by an on-board timer.

Sure but you also need to consider turn-off time - the fets don't stop
conduction instantaneously so you need some 'dead-time' when switching between
states. Some mosfet driver chips do this automatically for you btw.

It's very do-able.

I'd actually be tempted to do it with a look-up table that stores the switch on
and off states and increment the index with a timer.

Graham

 

Andy writes:
I like the PIC 16F84 . It is cheap, has a 20mhz clock, and
draws
about 5 mils --- costs about 5 bucks... Has on-board EEprom
memory and versatile built-in I/O . I've used it in several ham
projects...


Lots of PIC versions are available, and there are development
kits and programmers for sale very cheap.
Many have built-in A/D converters.

Also, a BASIC compiler is available....

It isn't the fanciest one, but for one-chip applications it does a
fine job. Just google up some info on it and plan to spend a
week or so learning to program it. It has a simple machine
instruction set. And a simple BASIC instruction set for the
BASIC compiler.....

Good Luck,
Andy W4OAH

 

Since when are car batteries 50V?

 

He did explain he was using a step-up arrangement.

Graham

 

New cars are supposed to be built with 42 volt batteries before
long. The charging voltage would be about 48 volts.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

Good point on the 48v charging system there Mike. I'll probably need
an alternator someday. This system could actually make a nice standby
power system to keep the furnace & radios running when power goes out.

Sorry, I forgot to mention that I am a power EE. I design large
inverters for a living. I've got a handle on the power side of things
like deadtimes and thermal management and so on - I'm just lacking on
the micro end of things. That's basically the whole motivation for
this project - a learning experience. I'm taking a 6 month sabbatical
from work and I would expect my next employer is going to want to know
what I did on my little vacation. If I end up with a piece of
hardware that might be useful then so much the better.

Ok on the pic Andy. I like hearing words like Simple & Basic. I'm a
keep it simple kinda guy. I'll look into that micro for sure - that's
the answer I was looking for.

Got my DD214 too - I'm just another tin can sailor outta Pearl

73
Bob
N9NEO

 

Did you happen to notice that most people bottom post on this board?

Don
Ex-W7SAT

 

Yzordderrex TOP-POSTED
(also BREAKING THREADING and ignoring context):
....and just for kicks changed the Subject line
to something without meaning to anyone else.

:: Andy wrote:
::I like the PIC 16F84
::

The PIC 16F84 is ANCIENT. If you can even find one,
it will cost you more than a newer, more able PIC variant.

Opinions differ on the "simplicity" of PICs.
One of my favorite descriptions of the PIC:
http://groups.google.com/group/comp...-*+immediate-addressing+A-good-place-to-start

Scroll down Lindan's post
and look at what he has to say about the AVR.

Note: That group (comp.arch.embedded)
is the place to ask questions about microcontrollers.

 

You can get motor control pic/mcu wich have the pwm module with the sine
lookup table already.
Im using a dspic30f2010 16bit with 3ch pwm wich would be able to do it
easily.

Colin =^.^=

 

Good for you!

Did you take advantage of the free meal at the Golden Coral
restraunts yesterday? I went, but their Monday menu isn't my favorite.



--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

Hi

Look at www.analog.com ADUC702x is my favorite. PWM-Features included for
gate-driving... AD and DA 12 bit @ 1 MSPS 40 MHz ARM7 core. Kits from $30 up
to $279 (with usb-JTAG included) where available (in january 2007:-(

Marte

 

Sure did notice that most bottom post here don.

73
NEO

 

Thanks for comments Jeff. And Yes, I'll be the first to admit I have a
lot of bad habits when it comes to posting on these forums. I've had
them a long long time and expect they will accompany me to the grave.
Thats ok with me.

When I changed the topic I was calling Andy directly to thank him for
the input. Andy told me to take a look at the Pic products, not just
the 16F84 in particular. I have heard others on other boards rave
about the Atmel parts and I am sure they make a nice part. I know they
have a large following. I am leaning towards the microchip products
for two reasons. I have found an application note that does exactly
what I need to do. I also have remembered that I worked with another
engineer many years ago that is well connected with microchip. He in
an independant consultant and writes application notes for them. I
have been in contact with him recently as he was looking for some
information from me. I will of course take a close look at the AVR
parts before making any decisions. The main criteria is cost and time
to learn. I'm presently in between jobs on a self imposed sabbatical
and I'm looking for some resume building exercises.

Thanks again for the input and if I have any Qs as the development
effort goes forward I'll be sure to post to comp.arch.embedded. Below
is a link to an inverter app note.

73
Bob
N9NEO
Just Say NEO!

http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en010947

 

Nope, we don't have that restaraunt up here in MA. No Waffle House
either that really bums me out. Mabe WH next week when wife and I
travel to PA to see her pappy.

regards,
Bob

 

"Virginia is for Lovers", Florida is for ol' farts ;-)

...Jim Thompson

 

And continuous top-posting is for rude people.

 

And you are SO jealous that we're accepted here, aren't you, Jim?


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

Arizona is for ol' farts, too ;-)

...Jim Thompson