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The British Amateur Television Club (BATC), produce some excellent software for the Raspberry Pi called 'Portsdown DATV Transceiver System'.
This Portsdown project provides an easy way to “get on air” with Digital ATV at a relatively low cost covering all of the commonly used DATV modes enabling it to be used for cross town QSOs, accessing ATV repeaters and for working the DX using Reduced bandwidth (RB-TV) modes.
The Portsdown software interfaces to the standard Raspberry Pi GPIO but what I wanted was to break this out specifically for my two DATV repeaters and combine with the necessary logic and HDMI auto switch on one PiHat board.
The SDK could of course be used for other Raspberry Pi projects and home automation.
DATV Repeaters GB3FWand GB3JT due be back on air during Q1 2025.
Alpha DesignWith an outline of what I wanted, the first stage was to break out all the GPIO's which the Portsdown software exposes.
Although it is understood that the GPIOs are largely for the standard user operation but by breaking out the various GPIOs based on the below matrix, it makes it easier for the board to be used for both purposes development cycles.
The Alpha board is essentially split into three :
- GPIO breakout into groups as detailed in the matrix. This brought out to standard 2.54 headers for easier experimentation and interfacing.
- HDMI switch, having three HDMI Mini Inputs and one HDMI Mini output. Controlled manually, automatically or via GPIO.
- On-board 5V 5A SMPS, suitable for 5 to 18V input. This then powering the board and Raspberry Pi from an external standard 12V power supply or car battery,
For reasons of speed and space, although I wanted to include an RTC, I have omitted a DS3231 and battery on the Alpha board. Same applies to the IR LED and driver circuits which are on my below wish list.
Tracking/layout is not currently optimized and the Alpha board only uses two layers. Eventual board will probably (maybe), end up four layers.
All passives are 0201 where possible as the board will become 'busy' once all the circuits are included.
The next stage of the design will flow from investigations using the Alpha board over Xmas (hopefully).
The base outline of the PiHat is taking most versions of the Raspberry Pi into account, so including additional millings to accommodate Pi needs.
My goal is to have a single PiHat, which contains all the DATV Repeater 'logic' and interfacing, together with an RTC.
If this board is of interest to you, please let me know. Equally, if you think of any other interfaces which could be added, ping me too.
NB. Now, I know the Raspberry Pi 5 has an RTC but this board may well be used on a Pi 4.
Wish List for the Board (expanding and WIP)- HMDI Switch (3 into 1)
- HDMI EDID EEPROM
- 12V SMPS (DC-DC), to externally power the Pi and board from 12V
- RTC with Battery (maybe rechargeable pending space)
- IR LED Control (TX/RX)
- Audio Matrix Switch (Reliable concept possibly based on my VMAC board)
- GPIO Headers
- Isolated TX PTT Output
- Isolated TX Power Amplifier Control Output
- Isolated GPIOs from Pi
- Isolated GPIOs from I2C Switch
Additional information, and other technical details on this project, maybe found in the related GitHub repository pages.
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, G8PUO. Maidstone, UK.
Electronics Engineer | Software Developer | R&D Support | RF Engineering | Product Certification and Testing | STEM Ambassador
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