For those who like computer control of PTT and COS, the ARS Serial Port EchoLink Adapter (SPEA) kit is the perfect choice. The PTT output can sink up to 500 mA. Active high or low COS input. Tx Key and COS activity LEDs. Low impedance, AC coupled, adjustable Tx audio output. High impedance, AC coupled, and adjustable Rx audio input.
This is a kit which requires soldering skills and wiring to interface to your transceiver and computer sound card. Requires a serial port or USB serial port adapter, and a computer running EchoLink software.