DTMF Link Controller

DTMF Tones are the most popular Repeater-Link-Echolink control method in Ham Radio.
CM8870 and Pic 16F628A based this circuit decodes DTMF tones and according to decoded tone sequence
change channel, activate/deactivate ctcss decoder, turn on/off repeater or control other settings.
For detecting tones, interrupt is used on pic, with the usage of correct components it is very fast.
Even 30ms tones are decoded perfectly.

I do not need any remote password change so I hardcoded all passwords. Actually I avoid this, because
if someone decode your tones, which is too easy, they can change your passwords. If you hardcode your passwords
they can only change settings but you can still activate it remotely.
If you want something more secure use one-time-password algorithms or something else.

The software is coded for 8 channel operation and on-off function.
In off state it does not turn the power off, simply not tx. Master password is not for daily usage but if someone try to play
your system you can turn the repeater off completely.
Pic will generate 75ms roger tone after all normal tx and 3 short beeps for accepted code and 1 long for denied code.
You can adjust the tone level via trimpot on the pcb.
Led is red-yellow, 2 legged led.



C Source Code Layout File
Components
U1 PIC 16F628A
U2 8870
U3 78L05
X1 3.5795Mhz

R1 270K
R2,R3 100K
R4 1K
R5 2K2
R6 1K

C1,C2,C3,C4,C5 100nF
C6 100uF