fx2adc: Using USB oscilloscopes as general purpose ADC
======================================================
:author:	Steve Markgraf <steve@steve-m.de>
:copyright:	2024 by Steve Markgraf (License: CC-BY-SA)
:backend:	slidy
:max-width:	45em


== Motivation
[role=""]

* Wanted to use vhsdecode (software defined VHS decoder)

image::hantek_black_snr.png[width="55%"]

https://github.com/oyvindln/vhs-decode

== Typical vhshdecode hardware

* Common hardware used are two clock-synchronized 'cxadc' cards
* Video capture cards based on CX2388x that can be used as general purpose ADC
** need PCI/PCIe-port
* 2x 40 MSPS @ 8 bit (FM audio, Video signal)

image::raspi_cx_crop.jpg[width="70%"]
* Mine hadn't arrived yet...

== Hantek PSO2020

image::pso2020.jpg[width="100%"]

== FX2 oscilloscope block diagram
[role=""]
image::usb_scope_block_diagram.svg[width="90%"]


== FX2 oscilloscope PCB
[role=""]
image::Hantek_6022bl_pcb_top.jpg[width="90%"]
[small]#Source: https://sigrok.org/wiki/File:Hantek_6022bl_pcb_top.jpg#


== USB oscilloscopes
[role=""]

Supported oscilloscopes:

* Hantek 6022BE
* Hantek 6022BL
* Hantek PSO2020
* Instrustar ISDS205A
* SainSmart DDS120
* YiXingDianZi MDSO
* LHT00SU1

== FX2 GPIF
[role=""]
ADC is connected via GPIF (General Purpose Interface):

* two 8 bit ports can be either used as 8 or 16 bit port
* limitation for 2 channel scopes
* either stream CH1 or CH1 + CH2
* CH2 alone with full sample rate not posible!

== FX2 GPIF clock modes
[role=""]
As a main clock for the interface you can select:

* 30 MHz
* 48 MHz (too fast for HS USB 2.0!)
* or add delay cycles
* IFCLK input

== Clock modification
[role=""]

image::pso2020_clockmod.jpg[width="100%"]

== Sigrok
[role=""]

* FX2-based oscilloscopes are supported by Sigrok
* Use that to capture data stream?
** This specific model was not supported yet by fx2lafw => added that
** libsigrok only uses a single USB transfer for FX2 scopes...

image::sigrok.png[width="100%"]

== libfx2adc

* Small library that loads (patched) fx2lafw and streams from the device
* Voltage divider (input gain) can be specified via commandline argument
* Checks if Si5351 is present, can use that to generate clock
* Uses AC coupling if present
* Usual rtl-sdr like tools:
** fx2adc_file
** fx2adc_tcp
** fx2adc_test


== VHS RF tap with USB oscilloscope

image::hantek_vhs.jpg[width="100%"]

== VHS RF spectrum

image::hantek_spectrum.png[width="65%"]

== fx2adc + R820T
[role=""]

image::hantek_r820t.png[width="68%"]

== FX2-based logic analyzer with analog input

image::T100-b-v1.2.jpg[width="75%"]

* All chinese components, ~24 USD
* Unfortunately ADC is connected to second 8 bit port, so 16 MSPS max

== Listening to DAB with LHT00SU1 + R820T

image::dab_lht00su1_crop.png[width="55%"]

== Summary

FX2-based oscilloscopes can be used for:

* extending bandwidth of rtl-sdr sticks
* direct sampling HF receiver (add some external LPF, amp)
* vhsdecode
* maybe scopehal + ngscopeclient?

However:

* need HW modification to get maximum sample rate
* more than one device connected to a single host don't work with 40 MSPS
** seems to be a limitation of USB 2.0 host controllers..

== Can you spot the difference?

image::hantek_6022_fx2_adc.jpg[width="70%"]

== Can you spot the difference?

image::pso2020_fx2_adc.jpg[width="90%"]

== EOF

* More information:
* https://github.com/steve-m/fx2adc

Other resources:

* https://sigrok.org/wiki/Supported_hardware#Oscilloscopes
* https://sigrok.org/wiki/Fx2lafw
* https://github.com/oyvindln/vhs-decode
* https://github.com/happycube/cxadc-linux3
* https://gitlab.com/jorgem-dev/cx88_sdr
{empty} +
{empty} +
{empty} +
{empty} +
* Questions?