It doesn’t get any simpler than this!
This interface uses the RTS and DTR signal lines from a cheap FTDI USB Serial Adapter, and provides isolated keying for both PTT and a CW key.
Problem!
The FTDI adapter provides signals that are +5V during receive and 0V during TX, but you cannot directly connect this to your transceiver, because your transceiver expects the PTT and CW key lines to be floating during RX, and not pulled to 5V.
These signals needs to be inverted so that an open-collector NPN transistor can be used to switch these lines to GND accordingly.
This simple circuit achieves this, and also provides isolated output using opto-couplers.
PTT and CW keying lines are identical, with only two components required for each as well as connectors to suit your transceiver.
Schematic
Four connections to the FTDI board are required, 5V, GND, RTS and DTR.
Theory of operation
Anode of opto-coupler LEDs are connected to +5V via 1k current limiting resistor.
With the transceiver in receive, the RTS and DTR signals idle at +5V, so no current flows, keeping LEDs off, and the optically coupled NPN transistors are therefore not conducting. ie; off.
When a signal line drops to 0V, ie; during TX or CW keying, current will flow, the LED will be on, activating the associated NPN transistor inside the opto-coupler, which switches that line to GND.
Construction
Beginning with the FTDI adapter, both the shunt and right-angle header is de-soldered.
Shunt was removed to keep a low profile, and is replaced with a wire link to the 5V side.
Circuit is constructed on a small piece of Veroboard.
Above: general layout of components – compare to schematic
X denotes cut in copper trace underneath
Right-angle headers are reused for solder points to PTT and Key wires.
Use drill bit to remove copper traces between IC pins and between resistor legs.
Ready to interconnect with FTDI board
Wire links used to interconnect:
• RTS
• GND
• 5V
• DTR
Finished Adapter
Solder the appropriate connectors to suit your transceivers PTT and CW Key jacks via 2-core cable, ie; speaker wire.
For the IC-7600, PTT is via the Accessory 2 7-pin DIN connector, and CW via ¼” stereo jack.
It sits out of sight behind the rig, so no fancy case required!
Wrapped in clear 20mm heat shrink.
COM Port Settings
To prevent unwanted keying and “Crazy Mouse” behaviour, the following Com Port settings should be applied to the FTDI interface Com Port.
Use Device Manager to confirm which Com Port the FTDI adapter is.
Windows:
Device Manager > Right click on Com Port
Left click Properties
Left click Port Settings
Left click Advanced
Deselect Serial Enumerator
Select Disable Modem Ctrl At Startup
OK
OK
That’s it!
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