Modem to Modem Problems

A "Short Circuit" to Happiness!


Soon after I got geoFax I tried faxing myself by directly connecting my own fax machine to my Boca 14.4 fax/modem via a phone cord. The idea was to use the fax machine as a scanner to bring some artwork into Geos. However, I ran into a problem. The fax/modem would not connect to the fax machine. I found this strange because the cheapo generic 14.4 fax/modem in my MS-DOS machine had no trouble making a direct connect to the fax machine, so I knew it could be done.

After talking to some good friends who know their stuff I learned that I probably needed some DC current on the phone line in order to prod the Boca into making a connect. I built this little circuit in a small plastic box and now it's an essential part of my Geos arsenal. Recently I upgraded the modem in the MS-DOS machine to a 28.8 Kb model and when I tried direct connect faxing found I needed this handy little box for it as well. I have seen people on FIDO experiencing problems connecting to various platforms with null modems too. This little box would probably solve their problems.


     in   -------------+---------------------+----------------------+-----------  out
                       |                     |                      
                       |                     |
               100     \                     +-----+
               ohm     /                     \     |
                       \               100   /     - LED     
                       |               ohm   \     ^
                       |                     /     |
                   +   |========             |     |
                        |  9 V.|             +-----+
                   -   |========             |                             
                       |                     |                         
     in   -------------+---------------------+-----------  out
 
The number of parts is very small, and you can omit the LED and it's resistor if you want. The basic principle is for the battery to simulate phone line current which these newer modems seem to need to connect. I packed all the components, including the 9 volt battery into a modular phone wall box, with the LED showing through the top. It lights only when you have a connection. The battery will last a LONG time.
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