This board is a universal radio project controller, with an ATMega328P(U) microcontroller and lots of options. The intention was for it to become a basic building block in transceivers, receivers, transmitters, signal generators, anywhere you need either a digital controller, one to three clocks, or both.
The board has headers for the common si5351 breakout board, available from Adafruit or as a .CN clone, and a 16x2 HD7044 Liquid Crystal Display using the standard 14+2 parallel data header (+2 for backlight). It brings out all of the available digital IOs (D2..D13), analogue inputs (ADC) A0..A5), as well as headers for a 12V supply, and access to the regulated 7805 5v output, access to the LCD backlight in case you wish to take control of this in software, and an FTDI-compatible USB-to-serial programming board.
Blog post with schematic: https://vk3hn.wordpress.com/?p=9360
However it doesn't end there, as the point of this desgn was to incorporate as many of the additional components that have so often been relegated to small boards hanging off front, side and rear panel sockets and switches. So there are these additional headers:
- a header for 1, 2 or 3 pushbuttons for general control purposes, intended to be mounted on a front panel for channel selection, VFO control, VFO step etc (additional buttons can easily be added in desired)
- a header for a paddle and 1, 2 or 3 keyer memory pushbuttons (again, more may be added)
- a header to take digitally generated and filtered sidetone (with an on-board level setting trimpot) off to a transcever's audio stage
- a header for a mechanical or optical emcoder (tuning), including a line for an integrated pushbutton.
The ATMega328 MCU's I2C SDA and SCL, ground and 5v are additionally available on an I2C header, for all kinds of extensions via sensors that talk I2C or those on breakout boards. This feature opens up the possibility of using any of the OLED displays instead of the LCD, as OLEDs interface via I2C. Another option is to use an LCD with I2C backpack which would free up 6 additional digital IO lines.
Blog: https://vk3hn.wordpress.com/
Github: https://github.com/prt459/Arduino_si5351_VFO_Controller_Keyer