THe PE1MUD/PE1OBW Digital Baseband is a hardware device to produce a baseband signal for analog FM television as used by radio amateurs. The baseband has an i2c interface which can be used to fully control it. This tool controls the baseband from a PC using a USB<->I2C interface. More information about the baseband can be found on https://fm-atv.nl.
The software presented here consists of two parts, a library baseband and
an example application baseband_config.
Baseband_config is a command-line program that supports export and import
of the baseband settings, read out of actual audio and video levels, upgrading
the firmware and more.
Interfaces based on two different chips are supported.
The FTDI chips do not support clock stretching. This limits the speed to 50 kHz and makes the tool unusable for some flash access commands (although firmware upgrading works). The FT232H is the only supported FTDI chip that offers true open drain outputs, but other FTDI devices might be used as well, using a workaround (diodes). See https://eblot.github.io/pyftdi/installation.html for more information.
The MCP2221A does support clock stretching, but it can leave the i2c bus in a 'hang' state when a transfer is terminated unexpectedly. I could reproduce this by terminating the program while reading the flash contents, after that SDA stayed low and the interface needed to be reset. This problem might be fixed in the future...
The software supports two MCP2221 Python drivers: EasyMCP2221 and PyMCP2221A. EasyMCP2221A works well with the latest version (1.7.2). On my machines, it operates reliable at 400 kHz. Overall speed is limited by the USB turnaround times, this is common for all chips/drivers.
The PyMCP2221A driver shows multiple issues. It works, somewhat, but it is not recommended as firmware upgrade doesn't work yet and I've seen it leaving the bus in a 'hang' state (SDA/SCL low forever).
Both the FT232H and the MCP2221A have a few GPIO pins that can be used together with the i2c functionality. The code contains a command to pulse a GPIO pin (active low), for example to reset the board remotely. For the FT232H, gpio's 3...6 are available, on the MCP2221A you can use GPIO0..3. On the MCP, however, the GPIOs seem to have predefined functions; I see GPIO0 pulsing at 50 Hz after the device is connected to the USB port...
You need a Baseband board and a supported USB <-> I2C interface. Connect the USB interface to the I2C header (4-pole) on the baseband PCB. For the FT232H, wiring is as shown below:
| FT232H | Baseband |
|---|---|
| GND | GND |
| AD0 | SCL |
| AD1 | SDA |
| AD2 | SDA |
| AD7 | SCL |
The baseband uses clock stretching, therefore both the AD0 and the AD7 line must be connected to SCL.
For the MCP2221A, wiring is straightforward: connect SDA, SCL and GND to the respective pins on the 4-pole Baseband I2C header.
To protect the FPGA, you could add resistors of e.g., 220 ohms in series with SCL and SDA. Leave the +5V on the Baseband unconnected!
Then install the software:
- Install drivers (if applicable)
- For the FT232H: follow the instructions on
https://eblot.github.io/pyftdi/installation.html. For Windows, you have to
install the 'Zadig' tool, and replace the existing driver with
libusb-win32. - For the MCP2221A: under Windows, it worked out of the box for me. For Linux, follow the instructions on https://learn.adafruit.com/circuitpython-libraries-on-any-computer-with-mcp2221/linux
- For the FT232H: follow the instructions on
https://eblot.github.io/pyftdi/installation.html. For Windows, you have to
install the 'Zadig' tool, and replace the existing driver with
- Download the codebase
- Install the tool with
pip install -e .(the-eoption installs the project in 'editable' mode) - Run the tool with
baseband_config [options]
Examples (replace --usb_easymcp by --usb_ftdi for an FTDI interface):
Show all options
baseband_config --helpShow baseband info (version and actual settings)
baseband_config --usb_easymcp --infoTo create a file with the settings, stored as json:
baseband_config --usb_easymcp --settings_to_file settings.json`The settings file can be modified and its contents can be written back. It is also possible to write back a partial json (i.e., only these settings will be modified). To write back to the baseband:
baseband_config --usb_easymcp --settings_from_file settings.jsonTo update the firmware and reboot when done:
baseband_config --usb_easymcp --upgrade baseband_0.26.bin
baseband_config --usb_easymcp --rebootChange some settings:
baseband_config --usb_easymcp --set fm.0.rf_frequency_khz=7020
baseband_config --usb_easymcp --set video.video_level=100
baseband_config --usb_easymcp --set video.video_mode=PAL
baseband_config --usb_easymcp --set "name=23cm TX"See the settings.py file for all possible fields in the settings string.
To store the actual settings to preset 10:
baseband_config --usb_easymcp --store_preset=10To enable the on screen display (overlay), turn off the menu and show some text:
baseband_config --usb_easymcp --set video.osd_mode=OSD_ON --set video.show_menu=0
baseband_config --usb_easymcp --clear_osd
baseband_config --usb_easymcp --write_osd "Hello\nYou can \iinvert\u text\0\0\0\0\0\0\0\0\0\0End of line"A '\0' inserts a 'transparent' space, a '\n' is a line feed and with '\i' and '\u' you can switch between inverted and normal text. Screen size is 40 x 16.
To send out your call in morse, with 15 words per minute, every 5 minutes on FM 1 and 2, with a 500 Hz tone at -12 dB:
baseband_config --usb_easymcp --set fm.0.generator_ena=1 --set fm.0.generator_level=2
baseband_config --usb_easymcp --set fm.1.generator_ena=1 --set fm.1.generator_level=2
baseband_config --usb_easymcp --set general.audio_nco_mode=NCO_MORSE --set general.audio_nco_frequency=500
baseband_config --usb_easymcp --set general.morse_message_repeat_time=300 --set general.morse_speed=1
baseband_config --usb_easymcp --set general.morse_message="PE1MUD"Note: the nco frequency is in Hz, level is generator_level * -6dB,
and morse speed is 30/15/10/7.5 words/minute for morse_speed = 0/1/2/3.
Screenshot:
