‰  NOW 40 WPM  ‰  
BOUNCE TIME DURING ACTIVATION IS INCLUDED IN THAT 300 US.  CAUTION SNUBBER
CIRCUITS, LIKE THE REVERSE BIASED DIODE ON RELAY COILS, CAN SIGNIFICANTLY
DELAY THE RELEASE TIME OF A RELAY WHEN THE DRIVER CONNECTED TO THE RELAY
INTERRUPTS THE RELAY COIL CURRENT.  THIS IS ESPECIALLY TRUE WHEN THE RELAY
COIL HAS A LARGE INDUCTANCE.  I CHOSE TO USE A DB 9 CONNECTOR FOR THE RADIO
I/O INTERFACE AND A 3R5 MILLIMETER TRS JACK FOR THE EXTERNAL SPEAKER.
SETUP FIRST, CONNECT THE INTERFACE TO YO

KEEP IN MIND THAT MOST TRANSMITTER VOX CIRCUITS REQUIRE THE PTT CIRCUIT TO
BE ACTIVE IN ORDER FOR THE TRANSMITTERS VOX FUNCTION TO OPERATE.  YOULL
PROBABLY WANT TO INCLUDE A TOGGLE SWITCH ON YOUR INTERFACE SO YOU CAN
GROUND THE RADIO PTT LEAD WHEN NEEDED.  MOST DIGITAL COMMUNICATION PROGRAMS
OUTPUT THE MODULATING AUDIO ON THE LEFT CHANNEL.  FLDIGI AND PERHAPS OTHER
PROGRAMS CAN ALSO BE CONFIGURED TO PROVIDE A 1 KHZ CONTROL SIGNAL ON THE
RIGHT CHANNEL AUDIO OUTPUT TO CONTROL THE PTT OF THE TRANSMITTER THAT IS,
WITH THE RIGHT CHANNEL CONTROL TONE PRESENT, THE TRANSMITTER KEYS ON, AND
WITH THE RIGHT CHANNEL CONTROL TONE ABSENT, THE TRANSMITTER REMAINS UN
KEYED.  I RECOMMEND USING THIS CONTROL TONE TO CONTROL THE TRANSMITTER WHEN
THE PROGRAM PROVIDES THAT OPTION.  THE ADVANTAGE OF USING THE RIGHT CHANNEL
CONTROL TONE TO CONTROL THE TRANSMITTER IS THAT THE AMPLITUDE OF THE
CONTROL TONE IS NOT RAMPED DURING ON/OFF TRANSITIONS.  WHEN ITS TIME TO
TURN ON THE TRANSMITTER THE FIRST HALF SINUSOIDAL CYCLE OF THE RIGHT
CHANNEL CONTROL TONE GOES TO FULL AMPLITUDE.  FLDIGI SOFTWARE ALSO PROVIDES
FOR FSK OUTPUT SEE PSEUDO FSK IN THE FLDIGI DOCUMENTATION.  WHEN THE PSEUDO
FSK OPTION IS ENABLED, THE PRESENCE OF THE RIGHT CHANNEL CONTROL TONE
REPRESENTS THE FSK MARK STATE WHILE ABSENCE OF THE RIGHT CHANNEL CONTROL
TONE REPRESENTS THE FSK SPACE STATE.  TO CONTROL THE TRANSMITTER WHEN THE

RIGHT CHANNEL CONTROL TONE IS USED FOR FSK, YOU MUST ENSURE THAT THE FLDIGI
RTTY DIDDLE OUTPUT IS ACTIVE.  THEN, THE RIGHT CHANNEL CONTROL TONE WILL BE
ACTIVE FOR AT LEAST ONE BIT OF EACH CHARACTER, AND THE DIDDLE FEATURE
ENSURES THAT CHARACTERS ARE CONSTANTLY GENERATED WHEN IN TRANSMIT MODE.
SO, IF WE ADD A 250 MILLISECOND RE TRIGGERABLE TIMER HANG TIMER TO THE
OUTPUT OF THE CONTROL TONE DETECTOR, WE CAN USE HANG TIMER OUTPUT TO DERIVE
A PTT SIGNAL FOR FSK.  THE FSK DRIVER TRANSISTOR, Q2, CAN BE A 2N3094 FOR
LOW VOLTAGE APPLICATIONS.  IF THE FSK CIRCUIT FROM THE TRANSMITTER IS HIGH
VOLTAGE, THEN USE AN MPSA42 FOR Q2.  FOR FLEXIBILITY, THE USER CAN SELECT
VIA SW3 EITHER THE LEFT CHANNEL OR RIGHT CHANNEL AUDIO OUTPUT FROM THE
SOUND DONGLE TO KEY THE TRANSMITTER.  COMPARATORS U2A AND U2B DETECT
POSITIVE AND NEGATIVE PEAKS, RESPECTIVELY, OF THE AUDIO CONTROL TONE.
RESISTORS R33 R36 ESTABLISH BIAS VOLTAGES ON THE COMPARATOR INPUTS SUCH
THAT WHEN NO AUDIO CONTROL TONE IS PRESENT AT THE INPUT, BOTH COMPARATOR
OUTPUTS ARE PULLED HIGH VIA R37.  THE COMPARATOR OUTPUTS ARE BOTH OPEN
COLLECTOR, WHICH MEANS THAT THE OUTPUT IS THE OPEN COLLECTOR OF AN EMITTER
‰  END OF 40 WPM TEXT  ‰  QST DE W1AW  ƒ