What circuit for computer audio out to key rig?

I recall W4BQF mentioning on his site somewhere that QRQ folks use sound card output to key their rigs. I'm wondering what circuit you guys use? Is the audio out just normal "sidetone" output?


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Hi Marc

Yes, normal sidetone... however the rise and fall time are reduced to zero to maintain proper timing since there is no concern for the quality of the audio to the ears, only the accuracy of the timing of the cw elements as the morse code tones are being converted from musical notes into a digitized "cw keying on/off signal". If you want to listen to the side tone however, you can keep the rise/fall time to your liking and adjust the weighting to compensate for the outgoing transmitted cw being lighter in weight than the original since some of the sine wave will not rectify until it goes above the threshold voltage of the diode circuits, thus trimming off some of the leading and trailing edges of each cw element.

Here is a DOC file that describes the circuit that I am currently using for "SOUNDCARD to RIG" cw:


You will have to watch out for RFI...which the article covers...
There are many other circuits that work.
This particular circuit I found to be very easy to implement.


Thanks very much Chuck! I'd like to use my iphone app to key my rig, this looks like it's worth a shot.


Here is a revised schematic with RFI CAPS in the circuit.(the two .001 caps on each secondary winding to ground on the isolation transformer) You have to put these caps in the circuit or the interface will lock in the keydown position if you get too much RFI in your station during transmit.  This interface is somewhat frequency resonant and will give the most voltage around 1600 hertz.   Adjust your outgoing cw tone to match this freq.for best results.  It will still work at normal cw tones but may perform better at 1600 hertz.

NOTE:  click on picture for better view

NOTE:  to match the cw element lengths to match original, use the FLdigi QSK CONTROL and adjust the post-keydown timing to your preference.  Usually this will be in the negative region.  Here is an example:

here is a picture of the interface (without showing the isolation transformer, the RFI caps, 1n914 diodes...
and including a 15 ohm output resistor-just a safety precaution, may not be needed ):

Below at the bottom is a PDF file from YPlog's Help Document that contains several circuits and descriptions for SOUNDcard interface circuits. See Attached PDF file below:
here are a couple of snapshots of the article:


Here is a PDF attachment from 73 AMATEUR RADIO TODAY JANUARY 1995 p32, 33


The article has a schematic and circuit board diagram for a more sophisticated method to make audio derived switches. You will have to modify a couple of caps for QRQ (c10)

wow, thanks so much for all the info Chuck!

What I have been using with YPlog for many years is the circuit posted by Chuck from the YPlog pdf file, labeled 'Sound Card Keyer for YPlog', the bridge rectifier circuit. I use a cheap Radio Shack audio transformer and instead of the 1N914 diodes, I use 1N4148 diodes (which just happened to be in my parts box..hihi). I use this same circuit with FLdigi (when I could get FLdigi to work!). So it has a frequency range of about 500 hz up to 6000 hz.
A computer's CPU in normal operation, will momentarily shut down it's I/O ports, meaning the serial and parallel ports, when ever it needs to do internal 'care taking', such as generation Windows sounds. This is what causes CW 'stuttering' when a program uses the I/O ports for CW keying of a rig. If one shuts off Windows internal sounds and uses only YPlog generated audio CW through this audio detector, you will never hear any CW 'stuttering'.

Tom - W4BQF
Here is a circuit and picture of another possible solution for CW AUDIO to CW KEYING from Ben, n6sl :

I thought it was a great idea to use a scrap/surplus 110 to 9 volt wall wart for the audio transformer.
On the circuit that I use for this, I was able to get over 2 volts instead of barely 1 volt when using the 10/1 transformer contained in this voltage adapter. It was not that difficult to "dig" it out of its case either...
This is a reply about the Windows interrupts problem with I/O port keying.  I wanted to point out that as a non-multitasking/multithreading Operating system, DOS works just fine for keying a rig via the serial port, using such software as cw500.exe.  I used to use that for my keyboard sending, and probably will again soon, at least until I get a dedicated hardware keyboard keyer that I like.

FROM: http://www.rason.org/Projects/tonekey/tonekey.htm

Recently, I received email from an amateur wishing to key his transmitter from the tone output of a Morse Code generator program. Although it is possible to connect to a COM port on the back of a PC using a diode-transistor configuration, this results in another precious COM port being used up. The tone keyer is an ideal alternative and works very well.

The circuit in Figure 1 is actually very similar to a circuit I used for an earlier VOX system. The circuit uses a 741 Op Amp as a comparator. Approximately 1/2 of the supply voltage is set for pins 2 and 3 of the Op Amp. The voltage across pin 2 is actually slightly higher than pin 3. This results in the output voltage at pin 6 to remain low with no signal.

When an audio tone is applied to C1, the voltage across pin 3 of the IC is slightly higher than pin 2 causing the output at pin 6 to go high. Because the output of the IC is pulsating in accordance with the tone frequency, capacitor C2 filters out the 700Hz output. Diode D1 prevents C2 from discharging through pin 6 when it goes low. Resistors R6 and R7 form a voltage divider network since the voltage from the IC could be as high as 1.5 volts in a low state. This keeps the voltage at the base of Q1 below .7 volts in a no signal condition. Transistor Q1 keys the transmitter by causing the PTT line to go low when a signal is present.

This circuit will work well using the output from amplified speakers or even connected to your PC speaker. The components are tailored for a 700Hz tone. If a lower frequency tone is used, C2 may need to be increased in value. R4 should be adjusted to just before the PTT line goes low. Some additional adjustment may be needed for best results.

The above circuit works well and does not tie up another one of those precious COM ports since many computers only have two available. If a high power transmitter is used, place this circuit in a shielded enclosure to prevent RF from affecting its operation...



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