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 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.