Control board

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:

  1. reset, data, data clock and update strobe for DDS1
  2. reset, data, data clock and update strobe for DDS2
  3. synchronous update strobe for both DDS boards
  4. drive signal for the detector’s atenuator switching
  5. 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.

Category: VNA
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