How to build a simple PTT interface for digital modes.

To continue on the theme of digital modes , i have prepared this tutorial on how to construct a PTT interface for your transceiver. This is very simple to construct and will cost only a few dollars and about 30 minutes of your time to make. The interface will allow computer control of the PTT line of your transceiver by using the DTR signal from the computers RS232 line (generally COM1).

RS232 PTT Schematic

RS232 PTT Schematic

As can be seen from this schematic. Very few components are needed to construct this interface.
In fact the entire device can be built into the DB9 D-Shell.

Using veroboard 7 holes x 4 holes solder pins 4 and 5 on the DB9 connector to the board. the remaining pins are not connected so remove the track that would connect to pins 2 and 3 on the db9. (fig 1)

You may need to fit the resistor at an angle for the board to fit inside the shell (fig 2). The LED is mounted on the solder side of the board (fig 3)

Finally attach the cable used to connect the radio’s PTT line and secure with the DB9 strain holder (fig 4).  Drill a 3mm hole for the led in one side of the DB9 D-Shell and Voila’ You have an RS232 to PTT interface.   In your software (FLDigi or MMSSTV) Be sure to set the ptt activate to DTR.


Interface_33( Fig 1 )solder side of board Interface_44

( Fig 2 ) Note the position of the resistor

( Fig 3 ) Note position of the LED
Interface_28( Fig 4 ) Attach the Strain holder.
If cable is thin use some tape as i
have to increase the diameter for the holder.

By Frank VK2BFC

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