NOTES:The SKC is designed to provide basic keyer functions for simple qrp rigs. It is particularly useful in Direct Conversion rigs, as it provides a means of generating side tone. Separate outputs for audio mute and transmitter keying provide sequenced audio muting and oscillator shift, allowing these to happen before and after the transmitter is keyed. This eliminates the need for R/C time constants in the auido mute switch(es) in the rig.
When not active, the keyer is in a low power sleep mode. While "asleep" the chip draws just a few microamps. This not only reduces current comsumption when the keyer is not being used, it keeps the internal oscillator from being heard in the receiver section of the rig its installed into. Sleep mode was added to chips shipped after 6/1/06.
The SKC could also be handy as a keyer to operate separate transmitter and receiver set ups, solid or hollow state. The audio mute output can be used to both mute the receiver, shift the Tx oscillator frequency (if needed) and operate the antenna change over relay, before the transmitter is keyed. It also provides the side tone, which separate Rx/Tx setups generally lack.
New external keyer mode - included in chips shipped after 3/7/07
Operation.
A single NO push button (MENU) is used to access the code speed settings, tune mode and Iambic A/B mode select.
Code Speed select:
A short push (click and release) of the menu button enters the code speed mode. The letter "S" will be sounded by the side tone. Code speed is then increased by tapping the DASH paddle and decreased by tapping the DOT paddle. A dot is sounded each time the code speed is changed, and a dot-dot (I) sounds when the limit of the code speed range is reached. If one of the paddle levers is not closed for about one (1) second, normal operation is resumed.
TUNE Mode:
A longer, one (1) second push of the menu button enters the TUNE mode. The letter "T" will sound by the side tone. The transmitter can now be keyed on by tapping the DASH paddle. The transmitter will remain on until you tap the DOT paddle to turn it off. This toggle on, toggle off feature frees up both hands for adjusting an antenna tuner.. To exit Tune Mode, click the menu switch again.
Iambic keying mode:
The default Iambic keying mode is B.
In this mode, if both paddles are closed, the keyer will send alternating dots and dashes. If the paddles are not released before the start of the element space, an extra dot or dash will be tacked onto the string.
Selecting Mode A.
Holding closed the MENU button for one (1) second past when the tune mode "T" is sent will toggle the Iambic mode to A. The letter "A" will sound when this happens. Releasing the MENU button now returns to normal operation, but with A mode enabled. This setting is not remembered by the keyer, so must be done after each power up.
Using a Straight Key:
The SKC will automatically detect a straight key on power up. Since "standard" paddle wiring is dot tip, dash sleeve, if the dash input is sensed to be grounded on power up, it is assumed a mono plug of a straight key is plugged into the paddle jack. This function also allows the rig to be keyed by an external keyer or computer. In this mode, the Mode switch has no function.
Stand alone (external keyer) mode:
This mode is used with rigs which already generate side tone and mute when transmitting.
If pin 5 is grounded on power up, stand alone mode is enabled. This mode disables the side tone output when keying. Side tone is still active when using the menu button, as these annunciation characters are not transmitted.
Connecting up the SKC.
The pin out and a typical wiring schematic is show below;
NOTES:
Tx keying and Audio mute output from chip are active high. 2N7000 mosfets are supplied to invert the signal as most rigs key and mute with active low signal. They also allow for switching voltages greater than the 5 volts the SKC operates at.
R1 is a required pull up resistor, as this port pin has no internal pull up. The value is not at all critical, anything in the range of 10 K to 100 K will work.
C2, 3 and 4 are required for static protection and help debounce the switch and paddle inputs.
R2, C5 and C6 are used to interface the side tone output with the audio stages of the rig. R2 and C6 form a low pass filter which helps make the square wave output of the side tone less raspy. Typical values for R2 and C6 would be 1 meg ohm and 0.1 uF. C5 is mostly used as a DC blocking cap, but can also be used to help set the side tone level. Depending of the gain of the audio stages following side tone injection, this cap maybe as small as 100 pF. If your rig uses a LM386, typically the pin 3 input is not used and is a good place to inject side tone into.
A small pizeo speaker could also be connected directly to the side tone output pin 7.
The +5 volts needed to power the SKC can come from a 5 volt regulator such as a 78L05 or a 5.1 volt zener and dropping resistor. Timing for the side tone and keying speed is derived from an internal R/C clock. Both voltage and temperature will affect the clock speed. For proper side tone pitch and keyer speeds, the supply voltage must be near 5 volts and be stable.
Noise: A 10 uHy RFC maybe needed in series with the 5 volt supply to reduce or eliminate noise generated by the internal clock in the chip.
Ordering:
Send $2.00 for each chip wanted, plus $1.00 for postage. DIP package only. Instructions do not come with the chip, print this page, as its all you need to know.
Steven Weber KD1JV
633 Champlain St
Berlin, NH 03570 USA