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Volume 001, Number 132, 5 Jul 1997

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  1. Re: Serial Port Alternatives by compass@xxxxxxxx
  2. Re: Serial Ports, Drawers, PC cards by compass@xxxxxxxx

Digest Articles

Re: Serial Port Alternatives by compass@xxxxxxxx


From: compass@xxxxxxxx
Subject: Re: Serial Port Alternatives
Date: Fri, 4 Jul 1997 08:23:03 -0700
MIME-Version: 1.0
Content-Type: text/plain
Content-Transfer-Encoding: 7bit
In-Reply-To: <199707021644.MAA21855@xxxxxxxx>



On Wed, 2 Jul 1997, Lo Len Smucker <lolen@xxxxxxxx> wrote:
>Ron,  
>
>>>> If I can be of help to anyone, let me know.>>>
>
>I have a modem for the Poqet but cannot find a serial port adapter that
>would go from the Poqet to the female (25 prong)plug on the modem.
>
>Would you have any idea as to where I could obtain same or how one could be
>constructed?
>
>Thanks in advance for any help.
>
>Len
>
>
>
>
=========================================================================
REPLY
=========================================================================
Hello Len,
  Yes, perhaps I can help. 
First, there is a company that makes a serial port that uses the PCMCIA (PC card) 
slot. This would be your easiest and fastest solution. The company that was developing 
it about three years ago was Prolinear (www.prolinear.com). I have seen the units 
advertised recently in Computer Shopper and distributed by Simple Somebody who also 
makes PC card modems.
   Then there is the second approach if you have some time to kill, enjoy a challenge 
and want to learn some new low-paying skills to dazzle your friends with.
   The Poqet is a truely unique machine in that the internal bus (yes, all of it!) is 
available to you without even opening up the box. The interface port on the back of 
the machine IS the internal bus. This means that it has all of the signals that you 
need. If memory serves, it is not hard to pull a serial connection out of the 
interface (I/O) port. If you know how to etch a double-sided copper circuit board, you 
can fabricate your own serial interface. A standard thickness double-sided 
copper-plated circuit board is just the right thickness to fit into the I/O port. All 
you need to do is cut out the size you need to fit into the port and then prepare the 
board for etching. Etch the board, solder some connections and your in business. 
   The modified RS-232 signals generated by the Poqet are at 5 volts. Internally 
within the Poqet, the signals are 3.3 volts. But the signals are run through a 'charge 
pump' which boosts the signal level up to 5 volts. This is why the batteries drain so 
much faster whenever you are using the serial port. The charge pump eats some juice to 
do it's stuff.
   Now, you will need to get a good book on how the RS-232 interface works so that you 
get it right. The classic is "RS-232 Made Easy" by I don't remember who. I will need 
to find the book and get the authors name again. 
   And beware, you will either need to only connect your Poqet to other instruments 
that work on 0-5 volts rail-to-rail, or you will need to add line buffer/drivers to 
your serial port design to keep from burning out the Poqet. If you fry your machine, 
don't say I didn't warn you. Normal RS-232 devices (including your desktop computer) 
operate at signal levels of +15 volts and -15 volts rail-to-rail. Notice that this is 
a total voltage swing of 30 volts rail-to-rail. The reason that they do this is to 
overcome noisy environments and allow the signal to travel long distances and still 
have enough voltage to get the job done.
   AGAIN, IF YOU WANT TO CONNECT TO NORMAL RS-232 DEVICES (read as "anything that 
plugs into the wall or uses more that four single-cell batteries in series") THEN YOU 
WILL NEED TO INCORPORATE "LINE BUFFER/DRIVERS" INTO YOUR SWERIAL PORT DESIGN. These 
buffer/drivers can be found at Radio Shack or any well stocked electronics store or 
catalog like Mouser or JDR and they cost less than a dollar each as I recall.
   I built one of these little boards once, but I was running solely to another 3.3 
volt device with a dedicated line, so I didn't need the buffer/drivers to protect the 
Poqet. But I couldn't use the cable to connect to anything else. If you have never 
etched a copper board before, it isn't hard, but there is a knack to it and you will 
probably try and fail five or ten times before you get a good board you can use. I 
know I did. There are several ways to prepare a board for etching either by using 
etch-resist(wax) or tape. The etching itself is really just a matter of dropping the 
board into a vat of ferric chloride (FeCl3) which is available at Radio Shack or other 
electronics stores. When the excess copper is removed, you pull the board out of the 
solution and rinse it off. Thats really all there is to it. Oh yeah, you will need to 
cut a little notch in the  board so that it will fit past the key in the I/O port.
   If you think that you would like to try the adventurous route I have outlined, then 
let me know and I will see if I can find a pinout for the Poqet I/O port so you will 
know what traces to etch on your circuit board. 
Cordially Yours,

Ron W. Hardy
Compass Consulting Co.
775 South Sunset Drive
Cedar City, UT 84720
voice:	801-865-7000
cell:	801-559-8000
fax:	801-586-5248
email:	compass@xxxxxxxx
web:	http://www.tcd.net/~compass/


Re: Serial Ports, Drawers, PC cards by compass@xxxxxxxx


From: compass@xxxxxxxx
Subject: Re: Serial Ports, Drawers, PC cards
Date: Sat, 5 Jul 1997 06:54:42 -0700
MIME-Version: 1.0
Content-Type: text/plain
Content-Transfer-Encoding: 7bit

Len, You wrote:
Ron, thanks for your time and "know-how." I do like a challenge and dazzling
my friends but I'm afraid I'd better go with your first suggestion for now.   

I thought I was doing pretty well when I extracted the pins in the hinges,
compressed them (reducing the circumference) and put them back after taking
out the spring at the site of the one hinge.  This was supposed to prevent
the hinge cracking that so many were reporting.  I then made a little holder
(from a hack saw blade - enclosing it in a cloth case) that fits under the
Poqet and holds the top/screen part in place when open. It works OK for me
and I'm hoping that it will increase the life of the Poqet.

If I go with the "company that makes a serial port that uses the PCMCIA (PC
card) slot", do I need to remove the card holder altogether? If so, does
this expose the Poqet to other possible problems, i.e. static charges, etc.?

One other thing, I recently found some PC cards that were shipped with the
original Poqet but they fit VERY tight and I'm almost afraid that they might
pull out the internal pins or something.  Is there a way to decrease the
too-tight fit?


Thanks again. 

Len


====================================================================================
Ron's Reply
====================================================================================
Hi Len,
   Check that your PC cards are not upside-down or backwards. The problem of tightness 
may also be with the drawer and not the connectors on the cards or the computer. Some 
of the better card drawers were built with one or two springs which press up against 
the bottom of the PC card to hold it it place tightly in the drawer which is no 
problem. One other potential source of tightness may be one or more bent connector 
pins. Pull out the drawer and visually inpect the pins to determine if this is the 
problem.
   Regarding needing to remove the drawer to use a PC card serial port:
1.  You may want to either remove the drawer if you use the serial port PC card only 
rarely and in a non-rugged environment. The PC card itself will cover the delicate 
electronics that you see under the drawer. In this case, the only real danger would be 
that you might bend the pins if you are not careful. 
2.  You may want to cut the exposed end off of the drawer to gain access to the 
connector built into the serial port PC card. If you do this, I would recommend only 
cutting off or cutting out as much of the end of the drawer as is necessary to gain 
the required access for your cabling. If you can leave any of the end in place, it 
will help stabilize the cards position in the drawer and allow you to use other cards 
as needed without compromise.
Cordially Yours, 

Ron W. Hardy
Compass Consulting Co.
775 South Sunset Drive
Cedar City, UT 84720
voice:	801-865-7000
cell:	801-559-8000
fax:	801-586-5248
email:	compass@xxxxxxxx
web:	http://www.tcd.net/~compass/



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