Clockgen Mod

Clockgen Mod

Previous Page CX Cards

Sub-Page RF Capture Guide

Next Page Hardware Installation Guide

What is this doc?

This doc is a 1 page version of Rene Wolfs clockgen mod setup wiki which is flushed out with more theory, this doc focuses on the basics of what goes ware and how to actually make captures, and also features the sane use of the SMA connector.

User Operation

Important

This Guide Assumes you have CXADC Installed and have tested your cards before starting modification of them and know the basics of capture with a CX Card, and have at least overview info about its mods, the clockgen + ADC mod assumes external amplifiers are employed for optimal signal to noise ratio of the raw signal's intended to be captured.

Important

C31 Mod & BNC Mod is normally recommended and assumed deployed with this mod.

Capture

Synchronised capture is all scripted into a single .sh file to run it simply download it and define the output path

Example:

./cxadc-vhs-sync-capture.sh /home/harry/Desktop

The Resulting Output:

RF Output is:

xxxx.xx.xx-xx.xx.xx-rf-audio-10msps.u8

xxxx.xx.xx-xx.xx.xx-rf-video-40msps.u8

Audio is 24-bit 3 channel 46875sps (46khz) file the mapping is:

Left/Right/Headswitch

You will want to map this to 2 separate audio tracks for muxing into a final video file.

The file set is automatically date stamped yyyy.hh.dd-hh.mm.ss

• Capture Script

• Collect Info Script

Auto Audio Aline

mono VhsDecodeAutoAudioAlign.exe gen-drift-csv --csv-output my-tape.csv --json video.tbc.json

Linux/MacOS users?

Alsamixer

Sample rate modes are the following:

28.63msps, 20msps, 40msps, 50msps

To open the terminal control window use:

alsamixer 

Press F6

Navigate with ↑ & ↓ keys.

Hit Enter with CXADC+ADC+ClockGen selected.

Press Space to enable audio control.

That is about it, you only play with these settings when doing manual overrides for stock settings.

Setup

Software Setup

Install asmixer

sudo apt install asmixer 

Run alsamixer with:

alsamixer

Fix Capture Script Permissions

chmod +x cxadc-sync-capture.sh

Pi Pico Firmware Flashing

Test Firmware / Clock Gen Firmware / Reset Firmware

Ensure Pi Pico is not plugged into the mainboard of the clockgen.

Equip a USB-C or Micro-B cable depending on your Pi Pico Type.

The Pi Pico displays as a USB storage device, simply drag and drop the test firmware onto the filesystem and it will automatically flash, if the unit blinks then its all good to reset and proceed.

To reset an Pi Pico Hold the button on it while unplugged then plug into usb, and use the flash_nuke.uf2 file to reset it to clean.

After a successful flashing this will show up as a microphone 3ch 48khz device to any systems sound manager application.

USB Connection

Internal USB headers can be used for the data connection to the Pi Pico

Normally PC's and Servers have internal USB 2.0 header's for basic devices.

Shielded Case & Bracket

As the audio ADC is unbalanced, and the clock gen board is sensitive to EMI due to high frequency clock signals being generated its recommended to shield the setup.

Copper Tape + 3D Printed Case

Debugging

Software Debugging

Check USB Devices with

lsusb

Check PCI & PCie Devices with

lspci

Device Busy

Test

arecord -D hw:CARD=CXADCADCClockGe -c 3 -r 46875 -f S24_3LE --samples=1000 test.wav

Result

arecord: main:831: audio open error: Device or resource busy

Solution:

Restart, try again

Hardware Debugging

PC Wont boot

This can be 2 key issues, bad SMA cable, or bad jig.

The Jig boards for the CX Cards are very sensitive, if a board is damaged or component then the board will not work.

Solution:

Reflow parts, if fail use another board, or replace all SMD components on PCB Jig.

Hardware Fabrication & Setup

PCB Fab - Here's the Gerber's I like PCBway but you can use JLCPCB or any domestic fab house or make them at home even have fun!

Is it worth using a PCB fab to populate parts? no not really doing it yourself is very easy and the price of having 2 boards populated, you can buy the tools and learn a invaluable skill, if not physically able then you can also ask in the discord or send off a email to Harry the community is always happy to help get hardware in hands.

Cables:

• 2x 50Ohm SMA to SMA 30-50cm Cable
• 1x 50Ohm SMA to BNC bulkhead 30-50cm.
• 2x BNC to BNC 50Ohm cables (Video RF + HiFi RF)
• 1x RCA or XLR to RCA cable (Linear or HiFi Ref)

Tools:

It's worth reading the Hardware Installation Guide if your new to soldering and or tools of the trade.

• 3rd Arm Clip Holder or Vice Clamp
• Soldering Iron / Bevel Type Tip
• 60/40 Leaded Solder (i.g Silverline or equivalent)
• Side Cutters
• 99.9% IPA
• Desoldering Gun or ENGINEER SS-02 Solder Sucker
• Desoldering braid

Parts:

• C - Capacitor
• D - Diode
• R - Resistor

Part Sizes

• SMA's are edge mount style connectors.
• SMD SOD-123 - Diodes
• 0805 SMD - Resistor & Capacitor

Jig Modified CX Card

Important

Ensure that the 3 parts C22, R12, C19 below the crystal package are removed.

Front & Back

Deployed (With and without 3D printed bracket)

Jig Board

Warning

Ensure all parts are populated in the correct orientation as shown in the image below.

• J30: SMA Edge Mount
• C1: 1.5 nF (6V or greater, ceramic X5R or X7R)
• C2: 10 nF (6V or greater, ceramic X5R or X7R)
• R1: 1K Ohm (5% tolerance or better)
• R2: 1K Ohm (5% tolerance or better)
• R3: 10K Ohm (5% tolerance or better)
• 2mm thick 25mm wide double sided foam tape.
• 26AGW wire in 4 colours, works well and is very available.

Mainboard

Warning

Always check via line indicator on SMD ports the polarity of diodes are in-line with indicator on PCB

There is 3 off shelf boards used for this:

AliExpress is most likely the cheapest place to source these but are very available on Amazon and other venders globally.

• Raspberry Pi Pico as the interface and control board via USB (you can use the stock one or USB-C ones)

• Adafruit Si5351A for generating the shared clock source with 5 potential inputs.

• PCM1802 ADC for L/R input Linear/HiFi audio capture.

Parts:

• SMA Edge Mount (On Headswitch/Ground Pads)
• C1: 10 µF
• R1: 1K Ohm
• D1: 3.3V zener diode
• D2: Generic switching diode

Sockets:

Header Socket Pin Size: 2.54mm

• U1: 2x 20-pin Header Socket (Pi Pico)
• U2: 1x 9-pin Header Socket (PCM1802)
• U3: 1x 7-pin Header Socket (Si5351A)

Board Parts:

• 1x Audio Cable (A 1m XLR cable is ideal as its shielded)
• 1x Pair of RCA or TRS audio connectors.
• 1x Small Zip-Tie or Cable-Tie (to secure audio line)

Interface:

• USB 2.0 Internal to Type-A or to Micro-B (or USB-C) cable

Note

The Si5351A kit headers are not recommended for socketed connectors, its recommended to solder headers then the board to said 2.54mm headers directly to ensure a secure connection.

PCM1802 Board

Note

The PCM1802 Board requires a boge wire bypass mod in most cases if 3.3v lines are not connected, its always good to test with a multi-meater if possible.

Parts

• PCM1802 Board
• 8Pin 2.54mm Headder

MODE0 with 3.3v Bridge Mod

Grounding

Finished Board (RCA as example)

Heatsinks

L 40mm X W 40mm X H 11mm heatsinks are readily available.

Amazon UK Silver / Black

AliExpress Black / Silver

Page End

Previous Page CX Cards

Sub-Page RF Capture Guide

Next Page Hardware Installation Guide