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Construction Manual for the K2DI v.III and K2DI-PCI boards © EA3BLQ - Revision June 2005
K2DI-PCI Computer Interface
Main features:
• The board measures 73 mm (2 7/8") x 35 mm (1 3/8").
• Its circuitry (see the schematics on page 29) features a Serial Port (RTS and DTR)
PTT or a VOX (Tone) PTT, to be chosen by the user when setting the J3 and J4
jumpers in accordance with his/her needs and/or preferences.
• The Serial Port is isolated by an optocoupler.
• The Line In/Mic or Line Out/Spkr soundcard connection is isolated by two
600:600Ω coupling transformers (Atech ATS-075), which feature a very flat
response and an Insertion Loss of 1.0 dB Max at 1 Khz 1 Vrms.
• One 10K POT controls the AF In audio volume level.
• A connection for an optional PTT ON Led is provided, to be installed in case this
board is used as an external stand alone computer interface.
• This board has been designed to be the K2DI's daughterboard but, as I have
pointed out, it also can be used as a stand alone external Computer's interface.
How it works:
PTT SWITCHING
The PTT circuit provides the possibility of using any of two modes of PTT switching: either
Serial (RS232) PTT or VOX (Tone) PTT, depending on the user’s choice or needs.
Many a program for digital communications (PSK31, SSTV, etc.), when setting-up the PTT
switching option, allows the user to choose either Serial COM port or Soundcard/VOX and,
when choosing the former, you can even choose the use of the RTS, DTR or both RTS &
DTR signals.
Serial (RS232) PTT
This mode features the use of an Optically Coupled Isolator, the 4N32, to achieve the
switching of the PTT while maintaining a very good isolation between the rig and the
computer. This Optocoupler (U1 on the schematic) is driven when any or both pins RTS
and/or DTR of a Computer’s Serial (RS232) connector (pins 4 and 7 on a DB9 and pins 4
and 20 on a DB25) are biased high (±5 vDC). When this happens the 4N32’s inner infrared
LED (pin 1 anode and pin 2 cathode) biases the photo sensor base so that the collector (pin
5) and the emitter (pin 4) become conductive and grounds the PTT line on pin 3 at P1, thus
switching the PTT circuit on.
Pins 1 and 2 at J4 must be jumpered. J3 must be open.
VOX (Tone) PTT
This circuit uses a Low Power Dual J-FET Operational Amplifier, the TL062 (U2 on the
schematic), and consists of two sections with different functionality:
In the first section (U2 a) a square wave signal is obtained from the AF signal coming from
the TR1 secondary and fed to pin 2. When the tension level on pin 2 is higher that that on
pin 3, the output on pin 1 will be at 0 (zero) volts level, and vice versa, when the tension
level on pin 2 is lower than that on pin 3, the output level on pin 1 will be that of ±5 vDC.
(35 paginas)
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