Imported from GitHub: lin20121221/101Things · commit bd0babd · license MIT

Description

A collection of cool projects to make!

README

Transmitter Examples

Microphone Example

transmitter_microphone_example.cpp

This is a very minimal usage example, the transmit mode and frequency are hard coded. Audio input is taken from a microphone using the builtin ADC.

Serial Example

transmitter_serial_example.cpp

This is a more complete usage example, the transmit mode and frequency are controlled through the USB serial interface. Audio data is streamed from a host PC via the USB serial connection.

The example may be controlled using the transmit.py utility.

Hardware Variations

The original transmitter used an FST3253 analog switch as a balanced mixer. In this design, two PWM outputs provide complimentary "balanced" inputs to the mixer. One non inverted output swings between 0 and VCC/2, the inverted output swings between vcc/2 and vcc.

The polar modulated amplifier behaves as an unbalanced mixer. It only requires a single PWM output that swings between 0 and vcc. However the second (inverted) pwm output has been retained as this allows ether inverting or non-inverting gate drivers to be used.

To allow both hardware variants to be used, two build targets have been defined for each of the transmitter examples.

transmitter_microphone_example_mixer.uf2 and transmitter_serial_example_mixer.uf2 support the FST3253 mixer design.

transmitter_microphone_example_polar_amplifier.uf2 and transmitter_serial_example_polar_amplifier.uf2 support the polar amplifier design.

Transmitter Serial Example Usage

A simple transmitter application is included in transmitter_serial_example.cpp. This allows the frequency and mode to be selected, and also to allow transmit data to be streamed through the USB Serial Interface.

The transmitter expects audio data in 8-bit signed format. The expected sample rate depends on the transmit mode.

==== ================ Mode Sample Rate kS/s ==== ================ FM 15 AM 12.5 LSB 10 USB 10 ==== ================

The sox utility can be used to convert from most common audio formats.

.. code:: bash

#generate a file to send in SSB mode sox FileToConvert.mp3 -t s8 -r 10k myfile.wav

Using the Python Transmit Utility

A simple python utility can stream audio files over USB to the transmitter.

To send audio using FM modulation at 10MHz.

.. code:: bash

$python transmit.py test_file_15k.wav Available Ports 0 /dev/ttyS4: n/a [n/a] 1 /dev/ttyACM0: Pico - Board CDC [USB VID:PID=2E8A:000A SER=E6609CB2D37B9828 LOCATION=1-1:1.0] Select COM port > 1 Enter Frequency Hz> 10000000 Enter mode AM/FM/LSB/USB > FM

To send audio using USB modulation at 14.175MHz.

.. code:: bash

$python transmit.py test_file_10k.wav Available Ports 0 /dev/ttyS4: n/a [n/a] 1 /dev/ttyACM0: Pico - Board CDC [USB VID:PID=2E8A:000A SER=E6609CB2D37B9828 LOCATION=1-1:1.0] Select COM port > 1 Enter Frequency Hz> 14.175e6 Enter mode AM/FM/LSB/USB > USB