VDAS Video Detect and Audio Squelch

Project outline

VDAS (Video Detect and Audio Squelch), is an ATV (Amateur Television), or CCTV (Closed Circuit Television), FPV (First Person View) quadcopter, accessory board.

With ATV, when using Analogue or Composite Video, the ability to automatically mute the channels thru audio upon no video sync, similar to a squelch circuit, can really help and assist for an improved operation for Amateur Television repeaters, ATV Portable operation, CCTV systems, FPV Radio Controlled Drone etc.

What does it do?

This small board detects a valid video sync (taken from an ATV receiver for example), with features including:

• Composite video sync detection using the MAX7461
• Un-mutes the through audio, only on a valid video source
• Supports the following standards, NTSC, PAL, and SECAM standard-definition television (SDTV) systems
• Advanced detection circuitry prevents false loss-of-sync alarms due to noise
• Includes an output FET for other switching purposes. This could be a small relay, LED, Transmitter PTT (Push to Talk), etc.
• Compact PCB only 45mm x 20mm x 5mm (Excluding BNC/RCA Phono Socket).
• Dual footprint pads for either PTH BNC or RCA Photo Socket, or wired.
• DC supply +6.5V to 16V A link can be made to bypass the LDO (remove LDO first) and operate at only 5V.
• The board operates within temperature range of -40°C to +85°C

These boards can be easily hung on the back of an ATV receiver. Great for receiver such as the old Comtech receivers and saves the unwanted thru noise on no signal.

With the increasing use of the FPV 5 GHz video receivers for ATV, the VDAS boards make a good companion. The VDAS board is used where the FPV includes audio from the drone, or aircraft, so that upon any loss of video, the thru audio automatically stops.

Note: The VDASwas originally placed on the HAMKit site (hence the logo on the board) but then I merged the two sites into the DitroniX.net website (saves web maintenance).

The board

The VDAS board is a small PCB (Size 45mm x 20mm x 5mm – excluding BNC which does not need to be fitted), that simply detects video sync (taken from an ATV receiver for example), and then provides a couple of outputs depending on the video state.

This video logic state is then used to mute, or un-mute, the through audio via an on-board high impedance FET switch, switch a separate output FET (controlling external PTT, Squelch Output, Relay etc.), and light an on-board status LED.

An on-board regulator allows DC input voltages from 5V to 16V, making this ideal for portable, mobile, repeater, home and FPV use.

Should you prefer not to use the on board 5V regulator, this maybe removed and the jumper pad on the PCB bottom soldered, in order to bypass the regulator.

A squelch tail (delay), of around 1 second holds up the SQL/PTT line during noisy signals. The timing can be easily changed through a 0805 resistor.

An additional feature of the VDAS board is that it also has a squelch detect FET output for other uses such as repeater TX PTT, LED etc.

PCB’s have four additional mounting holes and can also be provided in a row in order to allow easy mounting on a rear panel.

The BNC, or RCA phono socket, does not need to be fitted as the small header connector includes the video input too. This is useful in a compact wired system such as inside an ATV RX or FPV RX.

The board is designed to fit perfectly inside a Hammond 1551USB2TSK USB Case (optional).

How to use the board

To use, simply feed in a composite video signal and upon correct sync being detected, the following states are made:

• SQL/PTT output will go low
• The on board LED will light
• Thru Audio enabled.
• Changing a solder link, the output can be inverted, if required.

Connections

Connections are taken out to the mini JST 6 pin socket. (Cable supplied with 100mm open ended).

• 6-AF Input (Audio Input from RX for example)
• 5-AF Output (Audio Output to TX for example)
• 4-SQL Output (LED, PTT, Relay etc)
• 3-Video In (parallel to the BNC/RCA input)
• 2-GND
• 1-+6.5V to 16V DC In

The BNC connector can be directly exchanged for an RCA version, if required, as the PCB design includes dual footprints, and mounting holes, on the board to accommodate different manufacturers.

Should you wish, you may bypass the BNC socket and just use the Miniature 6 Way JST SH PCB connector for both Video input and Audio/PTT outputs.

Enclosure

All that is required in the case is a small hole for the BNC or RCA connector, depending on what you use. Some have been known to have only used the JST connector and then you are easily able to seal the enclosure to make watertight.

In the Full Kit: (Re-released end November 2022)

• 1 x HAMKit VMAC PiHat PCB (SMT Populated)
• 1 x JST mini 1 mm 6 pin cable approximately 150 mm
• 1 x BNC PCB Mount (not soldered to board - Optional)
• 1 x Hammond 1551USB2TSK USB Case/Enclosure (optional)

Supporting STEM

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