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'[EE]: Picpocket'
2000\11\06@175510 by Tony Nixon

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Hi all,

I posted a gif of the PICpocket PCB if anyones interested. It's the same
size as the PICstart B1 boards.

http://www.picnpoke.com/pcb.gif

Everything worked on a hand made PCB, fingers crossed for a produced one
:-)

I hate it when I get these back the first time as I always seem to spot
something I need to change.

I am using an RJ-12 connector for the ICSP as it provides an easy
interface. If this is not the 'norm' I can still change it. The pinouts
are in accordance with Microchips header connections in the ICSP
document - DS31028A.

1 - VPP 12.5V
2 - VCC 2V - 6V
3 - GND
4 - RB7 2V - 6V
5 - RB6 2V - 6V
6 - GND via OC driver <- my addition

It should be a nice bit of a challenge to build as it uses quite a few
surface mount parts although I enlarged the standard footprints slightly
to make soldering a bit easier.

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2000\11\06@212414 by Dan Michaels

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Tony Nixon wrote:
>Hi all,
>
>I posted a gif of the PICpocket PCB if anyones interested. It's the same
>size as the PICstart B1 boards.
>
......
>I hate it when I get these back the first time as I always seem to spot
>something I need to change.
>


Hi Tony, if I perceive your GIF correctly, you have a bridge rectifier
on the pcb, indicating you are possibly using an AC wall wart. If
so, then the v.reg filter caps should be huge - but looks like the
filter cap space provided is kinda small. If not so, then never mind.

- danM

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2000\11\06@235020 by Tony Nixon

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Dan Michaels wrote:
>
> Tony Nixon wrote:
> >Hi all,
> >
> >I posted a gif of the PICpocket PCB if anyones interested. It's the same
> >size as the PICstart B1 boards.
> >
> ......
> >I hate it when I get these back the first time as I always seem to spot
> >something I need to change.
> >
>
> Hi Tony, if I perceive your GIF correctly, you have a bridge rectifier
> on the pcb, indicating you are possibly using an AC wall wart. If
> so, then the v.reg filter caps should be huge - but looks like the
> filter cap space provided is kinda small. If not so, then never mind.
>

Hi Dan,

Just watched the Melbourne Cup (big event here - hic!) Won $6.00 wow :-)

You're right, I only catered for about 470uF at present, but the PCB is
still 'open' for awhile yet. I figured what I learnt at electronics
school - 1000uF / amp (ball park).

The final product will have the right choice and there is room for a
bigger cap.


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2000\11\07@115634 by Dan Michaels

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Tony Nixon wrote:

>
>You're right, I only catered for about 470uF at present, but the PCB is
>still 'open' for awhile yet. I figured what I learnt at electronics
>school - 1000uF / amp (ball park).
>
>The final product will have the right choice and there is room for a
>bigger cap.
>

Obviously wasn't too clear to me exactly what was up, as I was only
looking at an unlabelled pcb layout. The cap spacing looked smaller
- but then I wasn't really sure which were the caps - [Olin's right
- see what happens when you don't include "all" the comments - he, he]
:-).

Let's see ---

I/C = dv/dt --> 1A/1000uF = 1000v/sec
     --> 1v/msec --> 20v/20msec, where 20msec = period of 50hz AC

[Check my math - it's too early in the morning]. It says, if you suck
1A out of a 1000uF cap over the period of your AC input, then Vcap
will drop 20v. Yes?

- dan

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2000\11\07@192903 by Tony Nixon

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Dan Michaels wrote:
>
> Tony Nixon wrote:
>
> >
> >You're right, I only catered for about 470uF at present, but the PCB is
> >still 'open' for awhile yet. I figured what I learnt at electronics
> >school - 1000uF / amp (ball park).

Terrible advice me thinks.

> I/C = dv/dt --> 1A/1000uF = 1000v/sec
>       --> 1v/msec --> 20v/20msec, where 20msec = period of 50hz AC
>
> [Check my math - it's too early in the morning]. It says, if you suck
> 1A out of a 1000uF cap over the period of your AC input, then Vcap
> will drop 20v. Yes?

My heads a bit heavy from last night, but here goes..

12VAC 1A wall wart unloaded gives around 13.8VAC

The PicPocket draws 50mA quiescent and 100mA while programming.

Wall wart output with a 130mA load is around 13.6VAC

13.6VAC = 19.2VACPeak

1.2V drop through bridge = 18VAC peak

I need 13V + 2V min for 78xx regulation.

18 - 15 = 3V

Take a reasonable(?) margin and say 1V ripple allowed.

C = Iload / 2 X F X DV

C = .1 / 2 X 50 X 1  (60Hz for US even better)

C = 1000uF

Take a narrow margin and allow 2V ripple and I can use the 470uF.

Probably better with the 1000uF though, in case the ICSP circuit draws a
bit of current.

For about $2 more, could use LM2930-8 instead of 7808 for better ripple
margin.

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2000\11\07@194406 by Bill Westfield

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Of course, if you have a DC wall wart, then a bridge rectifier on the
board is a convenient well of isolating you from the polarity of the
connector...

BillW

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2000\11\07@201051 by Tony Nixon

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William Chops Westfield wrote:
>
> Of course, if you have a DC wall wart, then a bridge rectifier on the
> board is a convenient well of isolating you from the polarity of the
> connector...
>
> BillW
>

I just opened a new 12VDC 1A wart and got 15.6VDC with a 130mA load.

Minus 1.2V bridge = 14.4V.

That leaves 1.4 V which rules out a 78xx reg, but the LM2930-x will
work.

I am thinking, I will specify that regulator so I can use a DC wart and
then I only need smaller stabillity caps on the regs instead of the big
1000uF beasty.

I can also dispense with the bridge and use a single IN4001 to provide
battery reversal protection, and get an extra 0.6V.

That also leaves the wall wart open for other uses too if need be.

The savings on the cap and bridge can then help pay for the other reg.

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2000\11\07@211031 by Dwayne Reid

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At 12:09 PM 11/8/00 +1100, Tony Nixon wrote:

>I am thinking, I will specify that regulator so I can use a DC wart and
>then I only need smaller stabillity caps on the regs instead of the big
>1000uF beasty.
>
>I can also dispense with the bridge and use a single IN4001 to provide
>battery reversal protection, and get an extra 0.6V.
>
>That also leaves the wall wart open for other uses too if need be.
>
>The savings on the cap and bridge can then help pay for the other reg.

Watch out, Tony.  Remember that line voltage varies widely depending upon
location.  My products have to work over a 90Vac to 130Vac range (115 Vac
nominal).  At the low end of your range, I doubt that you would get the
minimum voltage needed.  Plus - remember that a LM293x starts to consume
much current when in dropout - this will reduce the available voltage even
more.

Why not check with your local burglar alarm supply places.  Over here, I
can get a 16Vac or 18Vac (large) wall warts with screw terminals rated at
40 VA for about Can $7.00 (from the wholesaler).  I use a fair number of
them: 12V gell cell chargers, RTS intercom power supplies, etc.  You have
to provide a rectifier but you'd have oodles of headroom.

Just a thought.

dwayne



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2000\11\08@010705 by Dale Botkin

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On Tue, 7 Nov 2000, William Chops Westfield wrote:

> Of course, if you have a DC wall wart, then a bridge rectifier on the
> board is a convenient well of isolating you from the polarity of the
> connector...

Yup.  I always stick a bridge in there, regardless of what I plan to use
-- it allows the use of any AC or DC wall wart, regardless of
polarization, as long as it falls within a reasonable voltage range.
Nothing I hate more than having half a dozen wall warts around, all the
wrong polarization or type.

Dale
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2000\11\08@011317 by Dale Botkin

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On Wed, 8 Nov 2000, Tony Nixon wrote:

> William Chops Westfield wrote:
> >
> > Of course, if you have a DC wall wart, then a bridge rectifier on the
> > board is a convenient well of isolating you from the polarity of the
> > connector...
> >
> > BillW
> >
>
> I just opened a new 12VDC 1A wart and got 15.6VDC with a 130mA load.
>
> Minus 1.2V bridge = 14.4V.
>
> That leaves 1.4 V which rules out a 78xx reg, but the LM2930-x will
> work.

78L12 is good for 140mA peak output current...  according to the data
sheet, the minimum input voltage needed for 12V regulated out is typ.
13.7V, max 14.5V, so I would be surprised if it weren't sufficient with
14.4V in.  You might want to try that.

Dale
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discoveries, is not "Eureka!" (I found it!) but "That's funny ..."
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2000\11\08@041624 by Alan B. Pearce

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>Yup.  I always stick a bridge in there, regardless of what I plan to use
>-- it allows the use of any AC or DC wall wart, regardless of
>polarization, as long as it falls within a reasonable voltage range.
>Nothing I hate more than having half a dozen wall warts around, all the
>wrong polarization or type.

Best idea going. Allows you to deal with fools as well. This is going a bit off
topic, but a company I worked for had a Sharp Laptop, and a Sharp LCD device for
putting on an overhead projector. When setting up a demonstration one day
someone plugged the power pack for the laptop into the LCD, only to find the LCD
did not work any more. The reason was the two power packs had opposite polarity
outputs - and both came from the same company!!!!!!!

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2000\11\08@091821 by staff

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Tony Nixon wrote:
{Quote hidden}

Tony, I have built a few small wall-wart type applications recently
using bridge rects made from IN1819's they are tiny, good for 1amp
and only drop 0.2v forward in low power apps. Pretty groovy.
They are becoming available in more and more "hobby" electronics
shops, but we buy them cheap in bulk anyway. :o)
-Roman

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2000\11\08@095941 by Dan Michaels

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Hi Tony,

Yes, my calcs show that the 1000uF/A rule of thumb will result
in excessive ripple, yours shows that 1000uF/(0.1A) will probably
be ok.

best regards,
- danM
=============


Tony Nixon wrote:
{Quote hidden}

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2000\11\08@125618 by Dale Botkin

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On Wed, 8 Nov 2000, Alan B. Pearce wrote:

> >Yup.  I always stick a bridge in there, regardless of what I plan to use
> >-- it allows the use of any AC or DC wall wart, regardless of
> >polarization, as long as it falls within a reasonable voltage range.
> >Nothing I hate more than having half a dozen wall warts around, all the
> >wrong polarization or type.
>
> Best idea going. Allows you to deal with fools as well. This is going a bit off
> topic, but a company I worked for had a Sharp Laptop, and a Sharp LCD device for
> putting on an overhead projector. When setting up a demonstration one day
> someone plugged the power pack for the laptop into the LCD, only to find the LCD
> did not work any more. The reason was the two power packs had opposite polarity
> outputs - and both came from the same company!!!!!!!

Well, the first time I used that was when it suddenly occurred to me that
a bridge not only won't interfere with using a DC power supply, it makes a
dandy polarity correction device as well.  I sent the customer a spec
sheet stating "Any AC or DC power supply with 7 to 24V output voltage, any
polarity".  They called and said they didn't want to pay for all that
extra power supply circuitry...  tee hee.  I told 'em it was a special
circuit we'd toss in for less than half a buck...

Dale
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discoveries, is not "Eureka!" (I found it!) but "That's funny ..."
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'[EE]: PicPocket'
2000\12\03@172442 by Tony Nixon
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Hi all,

Just thought I'd throw in an update on the PicPocket.

I got a professional PCB made up, mounted all parts including surface
mount, and while everything worked on my homemade board, the new one
flunked big time.

Anyway, "lots" of headaches later, it seems to be behaving itself.

It now programs PICs and can verify from a user programmable VCC range
of 2V - 6V.

I tested the ICSP and it works well over a 1 meter cable. It uses the
standard pinout as per Microchip specs, except an extra pin was added
which is connected to an open collector output so that OSC1 pins and or
RB3, or whatever can be pulled low while programming. This is via an
RJ45 type
connector.

The code and fuse disassembler/modifier is working ok.

I created a small FAT system to make the most use out of the on board
serial EEPROM - upto 64K for code storage. This will now manage up to 32
PIC programs.

Apart from stand alone operation, it also connects to Windows based
software and appears as a normal programmer interface - well, for my
programmer anyway ;-)

It now has a fully functioning Boot Loader which can program boot coded
chips and read/write internal EEPROM.

Operates via 4 push button switches and an LCD display which lets you
sift your way through the menu system - which has about 100 messages so
far.

Oh yes. Andy, it has the Parallax adaptor fitted as well. (I managed to
squeeze it onto the latest PCB design)

There is a GIF of the current design posted at

http://www.picnpoke.com/pcb.gif



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2000\12\04@161330 by Tony Nixon

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"David P. Harris" wrote:
>
> Hi Tony -
> Very exciting - when will this be available to the general public?
> David

There is a light at the end of the tunnel.

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