The 3’rd in the series is the control board.
It’s purpose is to allow easy interface from a single-board computer that has one SPI and one I2C port.
Also, it provides a common reference clock and a synchronous update signal to the two DDS boards, as required by AN-587
The SPI port is level-shifted to a MCP23S17-E/SP SPI to parallel expander.
The expander generates the following signals:
- reset, data, data clock and update strobe for DDS1
- reset, data, data clock and update strobe for DDS2
- synchronous update strobe for both DDS boards
- drive signal for the detector’s atenuator switching
- an unused software mode I2C, for a possible expansion
The schematic is here: controller
I’ve designed the DDS interface to allow synchronized and independent software control.
I want to be able to use the boards as the first and second mixer clocks in a heterodine receiver.
Or in any other application where 2 oscillators are needed.
On the same board there is a basic MOSFET I2C level shifter to adapt the 3.3 SBC signals to the 5V logic used in the entire VNA.
The rest of the board is just connectors for the 3 analog boards.
All of the chips on this board are trough-hole for no specific reason – I had enough space on the 100×50 template and i was bored of SMD’s
I don’t have a board picture for this, as it’s a pain to pull and reconnect all the headers.
