VMAC Video Matrix and Audio Controller

The VMAC Project Story

In building ATV (Amateur Television Repeaters), and DATV (Digital Amateur Television Repeaters), I had a need to easily switch a number of Audio and composite Video channels easily and remotely.

In a rather ambitious project, I looked at all of the requirements of the repeater and combined the wish list into a single compact design, which was called VMAC (Video Matrix and Audio Controller). This was originally developed my HAMKit branding.

The board is controlled using a Raspberry Pi Zero, although the header design was such that it could also be easily connected to a bigger brother Raspberry Pi (or other flavours of the PI's), if needed. Although principally be used with a Raspberry Pi, it could also be connected to other devices such as Arduino or Microchip, via i2c.

As you can see, the board has a lot on it and was initially designed to be hand placed.

The VMAC is a compact board that provides a very flexible Audio and Video Switching Matrix, with on-board DTMF Decoder, OSD Graphics, Video Signal Detectors and EEPROM.

Typical applications for VMAC :

• ATV and DATV Repeater Control Logic
• ATV home, mobile or portable stations
• FM Repeater Control Logic
• Audio / Video matrix controller
• ATV/DATV
• CCTV (Matrix or Auto Cycle Select)
• FPV (5GHz Video Camera Receivers)
• Video remote switching
• Audio remote switching
• Security CCTV

The VMAC is easily software controlled from the Raspberry Pi using your preferred coding language such as Python and all software provided is Open Source in order to encourage people to develop and help each other with ideas and applications.

Over a small period of time, the VMAC progressed and evolved into the more compact VMAC PiHat, with board sized at 85mm x 56mm.

In order to allow for additional inputs and increased flexibility, as VMAC PiHat evolved, the board was designed to allow it to be stacked.

Rather than use the RCA risers, I decided to use the simpler single RCA sockets and fan these around the PCB edge. This worked very well, more reliable and was also easier to populate and test.

With the ability to switch in an OSD (On Screen Display), looped through the matrix, the board functions brilliantly. The same matrix was also used to switch audio which proved equally reliable and allowed silent input switching.

The board includes video detectors which are then used to auto mute the incoming audio, so removing audio squelch noise if no composite video is detected.

A DTMF decoder maybe switched in to allow control of the board using DTMF over air.

The final production of VMAC was the VMAC PiHat V2.4 which had a revised SMPS and JST expansion header interface.

Default Configuration:

The default VMAC PiHat Input/Output configuration is:

Inputs

• 3 x Video inputs on AV1, AV2 and AV3
• 3 x Audio inputs on AV4, AV5 and AV6

Outputs

• 2 x Video outputs on AV 1 and AV 2
• 2 x Audio outputs on AV 3 and AV 4

These maybe altered by updating the input and output resistors and capacitors as shown in the schematic.

Supplied Built and Configured:

3V3A-2V2A

• 3 x Video Inputs (3 x RX for example)
• 3 x Audio Inputs (3 x RX for example)
• 1 x Pi A/V input (Test Card for example)
• 2 x Video Outputs (TX and Stream/Monitor for example)
• 2 x Audio Outputs (TX and Stream/Monitor for example)

Ready Built Kit:

• 1 x HAMKit VMAC PiHat v2.4 (Fully built, almost ready to plug into a Pi 2 or 3 and tested)
• 1 x Pi GPIO Header Riser Soldered for Pi 2 or 3.
• 2 x JST 6 pin cables
• 1 x Set of Pi mounting posts/bolts
• 1 x Pack of 0805 components (allowing change of input types if needed)

Evolvements

The VMAC PiHat evolved further into v3 and also a VMAC Mini, but these were placed on hold during an ESP32 version in 2020, which was subsequently mothballed due to life's commitments.

VMAC ESP32

The HAMKit VMAC ESP32 could be easily controlled from the on-board ESP32 WROOM 32D. Software developed such as using the Arduino IDE, Visual Studio Code and Platform IO IDE, Espressif IDF or Espressif ESP RainMaker.

Features

• Flexible Audio/Video Matrix
• ESP32 (with Wifi and BT)
• MQTT Home Automation Capable
• OSD (On Screen Display)
• DTMF Decoder
• 5 x Video Detectors
• 5 x Video Inputs
• 5 x Audio Inputs
• 5 x Squelch / RX Inputs
• DC Input 6-30V (Max32V)
• 3v3 and 5V PSU
• Synchronous 2A Bucks
• Matrix Video Output
• Matrix Audio Output
• PTT Output (FET)
• Relay Output (NC/NO)
• UART Programming
• Optional VMAC ESP32 BNC Riser

ATV Repeaters

Amateur Television has evolved massively over the years and is very much an active hobby and interest through out the World. This is largely supported by the BATC (British Amateur Television Club). - https://batc.org.uk/

Whilst my repeaters are unfortunately not on the air, largely due to house move and commitments, my plan it to get these back on during 2025.

Some photos which gives you an insight into the repeaters.

Future

It would be good to finalize the VMAC series, probably with an ESP32-C3. However, with the progression of HDMI, the humble composite video could be seen as too legacy - even though it is still current in many circles.

With the diminishing availability of parts like the MAX7461 and Max7456 series, an updated stance in design would need to be taken. That said, I feel it still has milage and may just continue to another chapter, if interest is shown.

Related project https://www.hackster.io/DitroniX/vdas-video-detect-and-audio-squelch-c76d9e

Other related boards

Portsdown Interface

DATV Repeaters

GB3FWand GB3JT will be back on air during Q1 2025.

NB. Will add more photo of the boards.

BATC - British Amateur Television Club

batc.org.uk

Further Information

Additional information, and other technical details on this project, maybe found in the related GitHub repository pages.

https://github.com/DitroniX

Repository Folders

• Code(Code examples for Arduino IDE and PlatformIO)
• Datasheets and Information(Component Datasheets, Schematics, Board Layouts, Photos, Technical Documentation)
• Certification(Related Repository Project or Part, Certification Information)

Repository Tabs

• Wiki(Related Repository Wiki pages and Technical User Information)
• Discussions(Related Repository User Discussion Forum)
• Issues(Related Repository Technical Issues and Fixes)

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Dave Williams, Maidstone, UK.

Electronics Engineer | Software Developer | R&D Support | RF Engineering | Product Certification and Testing | STEM Ambassador

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