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'[EE]: Yet another PIC (or AVR) based intelligent b'
2001\10\13@095630 by Wojciech Zabolotny

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part 1 1935 bytes content-type:text/plain; charset=us-asciiHi All,

For a few months I have been thinking about building an PIC or AVR based
intelligent NiCD/NiMH battery charger (however I couldn't find time
to acomplish it).
I have found a few nice projects, built by the others,
a) www.angelfire.com/electronic/hayles/charge1fig3.html
b) http://www.microchip.com/Download/appnote/category/rdesigns/30451c.pdf

However I still have some doubts. If one charges a 1.2V battery from eg. 5V
source without inductive elements, then the efficiency may not be higher
than ca. 25%. For the ideological (economy+ecology) reason I'd like to
make the charger as efficient as possible, so I'd like to use a kind of
DC/DC converter to efficiently charge my battery.

The proposed schematics is shown in attached files (no GIFs because of
LZW patent issues) in PNG and PDF format.
T1,R1,R6,D1 and D2 create switch with current limit (to avoid danger of
saturation of L1's core). R6 speeds up the switching off.
The Zener's diode D4 (eg. 3.3V) protects the voltage sensing input against
damage, when battery is disconnected (one may use the normal diode connected
in opposite direction to the PIC's Vcc).
R2 measures the battery charge current, and R3,C3 form the lowpass filter
for mean current measurement.
R4,R5 and T2 create the battery discharge system.
So one needs two A/D pins and two digital pins for each battery, and one PWM
output for all batteries (well it is possible to use two PWM output to
charge different size batteries simultaneously).
The device will use unstabilized AC/DC power supply, with additional low
power 5V stabilizer for PIC alone, so the overall efficiency should be
high...

I'd appreciate any comments/suggestions. The design when (or "if" ;-) )
finished will remain open source/open hardware.

--
                               TIA & Regards
                               Wojciech M. Zabolotny
                               spam_OUTwzabTakeThisOuTspamise.pw.edu.pl



part 2 2046 bytes content-type:application/octet-stream (decode)

part 3 5031 bytes content-type:image/png (decode)


part 4 3692 bytes content-type:application/pdf (decode)

part 5 105 bytes (decode)

2001\10\13@111937 by Roman Black

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Hmm, you can simplify it a bit, get rid of
R1, D1 and D2. You really don't need them.

You don't need D4 either for that matter.

For simplicity sake try a simple series
resistor before the battery, then take
two ADC taps, one before and one after the
resistor. This will give you battery voltage
and current.

In the SMPS trials I found you can use a
1mH or 1.5mH prewound tiny RF inductor,
good for 100mA, maybe even 200mA. These
are cheap and small.

My preference would be to keep it real simple
in hardware, then use the PIC for the other
stuff like current averaging and battery
testing. :o)
-Roman

Re the gif issue, you can also use the "ancient"
RLE format .PCX, works pretty good for 2 colour
circuit diagrams, and more people can access it.



Wojciech Zabolotny wrote:
{Quote hidden}

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2001\10\13@121450 by Ned Konz

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On Saturday 13 October 2001 06:53 am, Wojciech Zabolotny wrote:

> R2 measures the battery charge current, and R3,C3 form the lowpass filter
> for mean current measurement.
> R4,R5 and T2 create the battery discharge system.
> So one needs two A/D pins and two digital pins for each battery, and one
> PWM output for all batteries (well it is possible to use two PWM output to
> charge different size batteries simultaneously).

Well, your sense resistor R3 has to be very small for efficiency, so the
voltage will be very low (that is, if you want to limit losses in this part
of the circuit to 5%, then the voltage across the resistor will be roughly
60mV).

Unfortunately, 60mV is only about a third of the minimum PIC A/D +VRef of 2V.
My guess is that you'll want to amplify this sense voltage.

--
Ned Konz
currently: Stanwood, WA
email:     .....nedKILLspamspam.....bike-nomad.com
homepage:  http://bike-nomad.com

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2001\10\13@163834 by Olin Lathrop

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> The proposed schematics is shown in attached files (no GIFs because of
> LZW patent issues)

This is silly.  First, I thought Compuserve paid off Unisys for the right to
use LZW compression in GIF files a long time ago.  Second, I have never
heard of Unisys going after individual users of GIF files although they
clearly know it is going on a great deal.  Also, there are many free,
shareware, and commercial software packages that support GIF files, and I've
never heard of Unisys going after any of these either.  Again, I think this
is all due to the deal with Compuserve.  Anyone know for sure?


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olinspamspam_OUTembedinc.com, http://www.embedinc.com

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2001\10\13@164905 by Jeff DeMaagd

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----- Original Message -----
From: Olin Lathrop <KILLspamolin_piclistKILLspamspamEMBEDINC.COM>

> > The proposed schematics is shown in attached files (no GIFs because of
> > LZW patent issues)
>
> This is silly.  First, I thought Compuserve paid off Unisys for the right
to
> use LZW compression in GIF files a long time ago.

Likely for for Compuserve & their customers to make and use GIFs, but what
about everyone else?

>Second, I have never
> heard of Unisys going after individual users of GIF files although they
> clearly know it is going on a great deal.  Also, there are many free,
> shareware, and commercial software packages that support GIF files, and
I've
> never heard of Unisys going after any of these either.  Again, I think
this
> is all due to the deal with Compuserve.  Anyone know for sure?

Individual users no.  But Unisys has been very weird about the whole thing.
They let it go until it gets rediculously popular and supposedly they
started demanding royalties software companies that sell GIF capable
products.  IIRC Most commercial products have those royalties paid for.

The whole thing is silly and most individuals need not concern themselves
unless Unisys goes weird.

Jeff

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2001\10\13@172425 by jim korman

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Olin Lathrop wrote:

>> The proposed schematics is shown in attached files (no GIFs because of
>> LZW patent issues)
>
> <snip>

> Also, there are many free, shareware, and commercial software packages
> that support GIF files, and I've never heard of Unisys going after any
> of these either. Again, I think this is all due to the deal with
> Compuserve. Anyone know for sure?
>
> ********************************************************************

</snip>
I think that as long as you're using a commercial product to generate
the gif images, you should be alright. The company paid the royalty
for the algorithm!

Jim Korman

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2001\10\14@195400 by Peter L. Peres

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Unisys owns the patent on LZW and specifically permits the use of the LZW
in the GIF compressors and decompressors for non-commercial use only.
Commercial use requires a license. This causes many Open Source fans to
avoid GIF at any cost and many other people to avoid it too. It is not
clear whether a schematic published in a public forum in GIF format can be
'commercial use', even if it is posted by a registered firm.

Peter

PS: I am not a lawyer. The above reflects what I know about the issue.
Things may have changed very recently.

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