User's Manual

10
DESCRIPTION OF INPUT/OUTPUT
OPERATION
Turning the Transceiver On
Once power is applied to pin 6 of the radio the microcontroler will start and load the receive frequency of the
channel designated by CS2, CS1 and CS0 (pins 3, 2 and 1). The radio will beep out the channel number on
the speaker line.
Receive
The radio will monitor the channel until a carrier becomes present. When an on channel carrier appears, the
carrier detect line (pin 13) will be pulled high. If the correct CTCSS or DCS tone is present the radio will
unsquelch the SPEAKER and AUX_OUT lines.
Speaker Volume
The speaker volume is preset by an internal potentiometer (R350) to yield 2 volts RMS into 8 ohms. If your
application requires a different audio level two options exist. One is to open the transceiver unit by removing
the 4 corner screws on the connector end of the radio case, pull out the PCB and reset the volume
potentiometer (R350). The second is to place a power resistor or potentiometer in series with the output and
speaker to reduce or adjust volume.
Monitor
Pulling pin 11 low will cause the SPEAKER and AUX_OUT to unsquelch. This allows the operator to hear
any on channel signal.
Transmit
Pulling the /PTT input pin14 low activates the transmitter, and must be held low while transmitting. A
microphone with an internal PTT switch, with less than 3 k ohm resistance connected to pin4 will also
activate transmission when the microphone PTT is pressed. A programmable time-out-timer will shut down
transmission when /PTT is held down too long.
Shut down
The radio will shut down when the battery voltage drops below a predetermined “dead battery” level. This is
around 6 volts.