The G8TMV CTCSS encoder board Rev 4

CTCSS encoder board
The Rev 4 board is 35mm by 28mm and 5mm high, it is a major update to the Rev 3 board with a smaller size and lower profile.

The board comprises a voltage regulator, an MSP430 micro controller to generate the tone output and control the functionality of the system, an active filter to turn the voltage ladder from the 3-bit DAC into a sine wave and a trim pot to allow setting of the output level, plus a few ancillary parts to make it all work.

There is provision for a control button, an led and a PTT input.

The encoder is designed to run from 5 - 15v and draws approx 9mA. It makes sense to have the supply line switched so that tones are not generated during simplex operation.

The tone output is only active when the PTT input is grounded.

The tone encoder will generate any of the standard CTCSS tones used by the U.K. repeater system and some of the ones used in Europe. Other tones are possible, please contact me for details.

Each time the control push button is pressed the encoder moves to the next tone in the sequence. Each time a new tone is selected, and at power up, the LED annunciates the code letter for the tone in morse code.

A tone can be made the default by pressing and holding the push button until the LED flashes once. This stores the currently selected value in the micro controller non-volatile memory so that it will be used the next time the encoder is powered up.

CTCSS encoder board connections

The tones and their code letters are:

 A    67.0Hz 
 B    71.9Hz 
 C    77.0Hz 
 D    82.5Hz 
 E    88.5Hz 
 F    94.8Hz 
 G    103.5Hz 
 H    110.9Hz 
 J    118.8Hz 
 K    79.7Hz 

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