Pic 'n' Mix Digital Injection System

摘要

In this part the circuit diagram and PCB layout is provided for the DDS board, together with some construction notes and details for building a shaft encoder. Referring to Fig 13, the functional blocks comprise a crystal oscillator (the reference clock) feeding the DDS assembly, followed by a low pass filter and buffer. There are two output latches and not least, the PIC which controls operations. On the input side, the PIC is monitoring the shaft encoder, the PTT line and the keypad. TR1 is a conventional crystal oscillator, followed by TR2, a common gate buffer. The crystal may be any value in the range 100-125MHz,thehigherthe better. Theexact achieved frequency is trimmed into the software using the calibration process which will be described next month.