2 Port Repeater Controller
This is a 2 port repeater controller I designed and built specifically for linking a repeater on a mountaintop via a full duplex link to place where there is decent Internet connectivity. The design makes extensive use of SMT parts. There is a PIC16F876, a MT8870 DTMF encoder, and an Analog devices AD9833 numerically controlled oscillator for tone generation.  User I/O is done using the TI TPIC6B595 which has a shift register, output register, and 8 60V Open drain DMOS  FETs. The op-amps used in the audio section are National Semiconductor LMC6484.
The audio can be configured to be either flat, or pre-emphasized using the jumpers shown at the upper left of the picture. The controller draws less than 50mA at 13.8VDC. The audio 3db passband is flat from 50Hz to 6KHz. The code for the 16F876 is written in PIC assembler handles the ID'er, time out timer, audio muting, user I/O outputs, repeater mode (off, local repeat, linked). ID messages and the DTMF commands are programmable using DTMF configuration commands while the controller is unlocked.