This CTCSS tone encoder was designed for use with my Kenwood TM201B 2m transceiver. It uses the most *inexpensive* microcontroller on the planet; AVR Tiny11-6PC. The microcontroller is an AVR core microcontroller with minimum number of peripherals. Although this micro has an in built 1 MHz oscillator, the micro is clocked using a 32KHz XTAL to generate a stable clock. The internal oscillator is not calibrated and the clock varies with voltage and the temp of the device.

The unit is right now programmed to generate one tone but there is an option for four tones. The two IO pins of the micro are left aside for tone selection input. The tones can then be selected by the jumpers.

The Kenwood TM201B transceiver has an option of adding a tone board TU-3. The module is hard to find and expensive. After doing a lot of digging, a Kenwood engineer helped me with the TU-3 Datasheet.

Click here to open the TU-3 dataseet