Many UK cave rescues teams have used “Michie” type field telephones for many years with considerable success, reliability and ease of use.  These phones run over kilometres of just a single wire, with the return audio signal passing through the ground, and they have a runtime in days on Duracell type batteries.


About 30 new handsets and 8 base stations were built in 2013 to replace ageing equipment, some dating from the 1980s, and it has been issued to various rescue teams.  The latest design incorporates an improved Michie type of audio circuit, together with new chips to provide battery management, more features and control by software.


This webpage is intended to document the project for anyone wanting to build sets for themselves or to repair the 2013 sets.  The following links download zip files containing:


PowerPoint end-user guide and sound wav files [4MB]


PCB artwork and phone PIC software in MP-ASM [30KB]


CREG Journal article, circuit diagrams, bill of materials, phone building guide [4MB]