A Paddle-Only Sidetone for Winkey

I am in the process of transitioning from TRLog to N1MM Logger as my contest logger-of-choice. One excellent feature of TRLog is the ability to connect a paddle directly to a parallel port, and have paddle-sent CW generated by TRLog. TRLog also supports a sidetone that is generated by the PC speaker, only for paddle-sent CW. I am one of the many SO2R operators who completely mutes the sidetones generated by the transceivers, so that they do not interfere with my concentration on the S&P radio while the Run radio is transmitting TRLog-generated CQ's and exchanges. The TRLog paddle-only CW sidetone produces output to the PC speaker which allows me to be able to hear my paddle-sent CW, without the need for transceiver sidetone.

N1MM Logger does not support a parallel-port paddle interface. Many N1MM Logger users use a separate keyer for their paddle-sent CW. This has the disadvantage that the paddle-sent CW cannot interrupt the N1MM Logger-generated CQ's and exchanges. An alternative, that many N1MM Logger users have implemented, is to use the inexpensive Winkey interface (www.k1el.com) for generating CW. Not only does Winkey support N1MM Logger-generated CW, but it supports a paddle input that can interrupt N1MM Logger-generated CW. An "almost" perfect replacement for TRLog. The one element that is lacking is a paddle-only sidetone. This circuit, when used with Winkey, provides a paddle-only CW sidetone.

Circuit Description

The circuit shown above was produced entirely from components in my junkbox, or readily available at my small-town (i.e. limited inventory) RadioShack. I'm sure there are simpler ways to achieve the same result.

The fundamental idea behind the circuit is to produce a CW sidetone only when Winkey outputs CW and when that CW was generated from the paddle input. To determine when there is paddle input, the voltage at the junction of Winkey R6, R9 and R10 is monitored. A voltage greater than 3 volts indicates that neither paddle is active. A voltage less than 3 volts indicates that either the dot or dash paddle, or both is active. This voltage is applied to U1A, configured as a comparator, whose level is controlled by a voltage divider made by the 3.6K and 10K resistors. When either paddle is active, the output of U1A goes high, and is held high for several hundred milliseconds by the 1uf capacitor and 220K resistor. U1B is a buffer, isolating U1A from the low impedance input of the 2N2222. The 2N2222 is a simple switch, applying +12 volts to the 555 timer when either paddle is active. The 555 timer is configured as an audio oscillator. It is turned on when both the 2N2222 is turned on by paddle activation, or when the Winkey key output is grounded. The audio output of the 555 is DC-blocked through the10 uf capacitor, and its level set by the 470 ohm resistor. The output is more than sufficient to drive headphones.

Nothing is very critical in this circuit design. U1 is any dual op-amp. My RadioShack used to sell them; your mileage may vary ! IC1 is a 555 is a timer, still available at my RadioShack. The 3.6K and 10K resistors making up the voltage divider are not critical - any values that form a voltage divider of about 3 volts will work. The 1 uf capacitor and 220K resistor can be replaced by any pair that provides a few hundred millisecond time constant. The diodes can be any silicon diodes. The combination of the 10K resistor, 22K resistor and .05 uf capacitor connected to the 555 determine the audio tone, and can be changed. The 470 ohm sidetone output resistor can be replaced by a potentiometer to allow the sidetone audio level to be varied. The 10 uf DC-blocking capacitor can be any value of 10 uf or greater.