Red Pitaya - preliminary work

Update 2019 August 2

The instructions at https://github.com/jbrzusto/dar now supersede those on this page, wherever
there is disagreement.  In particular, we're going back to a previous version of the redpitaya
image.

Update: 2019 April 24

Please note that the connections for AZI and HDG were reversed in versions of this page
before today.  AZI connects to pin 13, and HDG connects to pin 14.

Update: 2019 March 28:

New software releases, still not ready for end users:

• image for the redpitaya SD card
• image for the Raspberry Pi 3B+

Note: these releases are .ZIP archives whose contents should end up in the top-level
directory of a VFAT-formatted micro SD card.  i.e. they are not disk images.  You can:

• download the .ZIP archive
• unzip it to a folder on your desktop
• drag the contents of that folder directly to an SD card on your desktop

The red pitaya board (version 1.1, aka STEMlab 125-14) can be adapted to work as a digitizer for pulsed radar.

We don't yet have a radR plugin to use this board, but the basic approach is:

• use high-speed (125 MS/s) 14-bit ADC-A for video;
  set jumper for +/- 1 Volt input
  use resistor network for impedance matching
   
• use high-speed 14-bit ADC-B for trigger
  set jumper for +/- 20 Volt input
   
• use low-speed (100 kS/s) 12-bit ADC for ARP / heading (Analog input 1 = E2:pin 14);
  use resistor network to adjust range, limit current draw
   
• use low speed 12-bit ADC for ACP / azimuth (Analog input 0 = E2:pin 13);
  use resistor network to adjust range, limit current draw.

Pinout for header (extension connector E2) on which Analog Inputs 0 and 1 are available is here:

http://redpitaya.readthedocs.io/en/l...sion-connector

Front-end resistor networks are used to match impedance on the video line,
and to limit voltage range on the other three lines.

The forked version of the red pitaya source code base that supports this application is here:

https://github.com/jbrzusto/digdar

An image for a 4 GB micro SD card generated from the source above is here:

http://discovery.acadiau.ca/radR/redpitaya/

A capture utility that grabs from a networked red pitaya into sweep files is here:

https://github.com/jbrzusto/capture

Two of these boards have been deployed on radars:

• Bridgemaster E 25 kW with 8' open array antenna, at the FORCE visitor centre (since Nov., 2014)
• Furuno FR8252 with 6' open array antenna, at the Cape Sharp Lighthouse (since May, 2018)

Images: