Circuit Lake

Electronic Project and Circuit Collection

Home-made Sound Card Interface

03/27/2010 Category: Audio, AVR, Control, Interfacing

The PSK31 (Phase Shift Keying, 31 Baud) Adapter is a hardware interface between a PC running a digital communications program, such as DigiPan, and an Amateur Radio transceiver. The electronically adjustable PSK31 interface is controlled by microcontroller AVR ATmega8. It provides automated adjustment and optimization of the audio levels that are carried between the PC and the radio transceiver.

AVR Project Sound Card Interface

The PC, running DigiPan, synthesizes a digital waveform that is modulated with the data that the user wishes to transmit. This modulated signal is passed to the PSK31 Adapter where a digital Poten can adjust the volume level that is passed to the radio transmitter. An RF tap connected to the transmitter’s antenna provides insight into the state of the transmitted signal.

On the receive end, the radio receiver’s audio output is passed through a second digital potentiometer and into the PC for demodulation. The absolute audio level is compared to a programmed threshold to adjust for a signal level that is too low or too high.

The PC’s RS-232 handshake signals are routed through an opto-isolator to generate a Push-To-Talk transmit signal. The PTT signal is also routed to the PSK31 Adapter to be used to determine if the system is in transmit mode or receive mode. PSK31 Adapter project is designed by Steve Lubbers.