The MacGuffin Project

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The MacGuffin project is a collection of tools used to create an automated multi-band ATV system based on the Portsdown transmitter and the Ryde receiver. An RF path from the Portsdown or the Ryde to an antenna is created by using relays to select the appropriate intermediate equipment. This includes RX preamps, TX drivers and power amplifiers. Transverters may also be a part of the system.

The system automatically connects the components for the band selected by the Portsdown and sequences the transitions between RX and TX. An Arduino Nano and MCP23017 IO expanders are used to generate control signals. They operate the relays used to select the RF paths connecting the components for the various bands. PTT and DC power to the amplifiers is also controlled.


PCBs have been designed for the Nano and the MCP23017. The Nano board has circuitry to interface with the Portsdown and other equipment. The IO expander board is designed to easily connect to a 16 relay module from eBay or to user-selected relays through optional drivers or logic level signals. A builder could choose to use modules from eBay instead of the MacGuffin PCBs.


There is no standard MacGuffin configuration as it is expected that each builder will be using parts in hand or the parts that are available at the time they are building. The documentation does include examples of various possible configurations and a list a RF relays available at the time the design was started.

The first step in designing the system is to decide which bands will be used. That starts with the setup of the Portsdown. Next a relay configuration can be planned which will switch the RF through the appropriate equipment for each band. Then a basic Arduino sketch is modified to match the builder’s Portsdown configuration and the relay configuration. Modifying the Nano application does not require knowledge of the Arduino programming language. Tables in the sketch determine the control of the relay paths and the text displayed on the LCD.

This block diagram shows the basic structure of a MacGuffin system.

Block diagram McGuffin.png

Files below are contained in these zip files.

File:MacGuffin Arduino

File:MacGuffin Main

Educational material

These documents describe different aspects of the MacGuffin system. In addition to reading these notes look over the other documents to get a fuller picture of the MacGuffin capabilities. This will help design your MacGuffin hardware and modify the Arduino sketch. MacGuffin General Notes V2.docx MacGuffin Sketch Notes V2.docx Information about the Arduino sketch MacGuffin User Bit Patterns.docx User Defined Bit Patterns explained by an example MacGuffin Relay Configurations.pdf Examples to show use of RF relays < MacGuffin IO Definition page>File:W MacGuffin IO Definition.docx IO Port Definition explained by an example

Here are the things to build or buy.

<MacGuffin Hardware page>File:W MacGuffin Hardware.docx


MacGuffin_Sequencer_V3-0_19FEB2022.ino Arduino sketch to be modified for your system I2C_SCANNER.ino Utility for checking the I2C devices addresses to see they are present and correct.

===Software worksheets=== Plan and record information for modifying the sketch MacGuffin Band Assignment .xlsx Record band from the Portsdown setup and your relay configuration MacGuffin IO Expander Assignment V2.xlsx Record the IO expander port setup MacGuffin User Bit Patterns.xlsx Record user bit patterns for use with the IO expander ports.

Your files

Generate these files to plan your MacGuffin.


Drawing of relay configuration – RF relays and DC control relays Drawing or spreadsheet of IO port connections


Band assignment spreadsheet IO expander assignment spreadsheet User defined bit pattern spreadsheet(s) if used Modified copy of Arduino sketch

File:MacGuffin Hardware

File:MacGuffin 6P