Taking cave rescue telephones forward
Download
1 / 15

Taking Cave Rescue Telephones Forward - PowerPoint PPT Presentation


  • 87 Views
  • Uploaded on
  • Presentation posted in: General

Taking Cave Rescue Telephones Forward. Stuart France. WHY? Single-wire field telephones remain the most reliable and straightforward comms tool for cave rescue in Wales. The 1988 version. Second-hand BT “4T” earpieces as mic/spkr DPDT toggle switch for PTT function

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha

Download Presentation

Taking Cave Rescue Telephones Forward

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Taking Cave Rescue Telephones Forward

Stuart France


WHY?Single-wire field telephones remain the most reliable and straightforward comms tool for cave rescue in Wales


The 1988 version

  • Second-hand BT “4T” earpieces as mic/spkr

  • DPDT toggle switch for PTT function

  • STDT toggle switch for on/off

  • 9 volt PP3 battery

  • No call tone facility

  • PCB potted but switches vulnerable

  • Diecast box, no gasket, earth connection

  • Line connection as flying lead with croc clip


The 1988 version (sort of)


What happened in practice?

  • Turned on by accident  flat battery

  • No LED  turned off by accident

  • Toggle switches snapped

  • Stored damp or with water inside box

  • Corrosion of wires / switches

  • No way to get the attention of called party

  • Speech level fades as battery drains

  • PP3’s not easy to get in a hurry


Nigel Lovell version

  • Better box and construction standard

  • Higher line impedance

  • LED flashes once when turned on/off

  • Other people have added 4000 or 74 logic chips for tones etc, but basically they are all much the same as “1988”


Has anything happened in the past 20 years?

  • Microprocessors costing 50p

  • Software seen as an asset not a risk

  • DC-DC power supply chips

  • Battery technology advances

  • The iPod generation grow up


Updating the phone spec

  • Single SPST push-button interface

  • 3xAA alkaline to 12V DC-DC step-up

  • Microprocessor for:

    • Analysing push-button gestures

    • Power on/off function, low battery warning

    • LED signalling

    • PTT function

    • Tone generation

    • Upgradeable software


Ruggedization

  • Brand new military spec “4T” earpieces

  • Diecast box with a gasket

  • IP68 push-button not toggle switches

  • Screw terminal post for line connection

    • Croc clip lead as an accessory

  • Circuit and switch wiring potted

  • 3xAA Battery holder replaceable


The development version


Push Button

  • 3-second push to power it up

  • Once running:

    • Push and hold to talk, as per normal

    • Double-click to send a call tone

      • Click or timeout to end call tone

    • Quad-click to power off


Tone Generation

  • Power on/off sound

  • Warbling call tone

  • Roger bleep after a transmission

  • Short bleeps for low battery warning

    • Once a minute?


LED functions

  • Intermittent flash while turned on

    • Every 10 secs?


2009 Prototype

  • PIC12F629 with 6 I/O lines in a DIL8 device

    • Good for 2.5 to 5.0 volts, in-circuit programmable

  • MAX761 converts 3xAAs to 12 volts

    • Starts up at 2.5V, low battery logic output to uP

  • One push-button switch

  • Relay instead of the DPDT toggle switch

  • Diecast box with gasket

  • NATO specification tropicalized 4T earpiece

  • Audio circuit as per Nigel Lovell

  • Screw terminal post for line connection


ad
  • Login