Taking Cave Rescue Telephones Forward Stuart France

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  • Taking Cave Rescue Telephones ForwardStuart France

  • WHY?

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

  • The 1988 versionSecond-hand BT 4T earpieces as mic/spkrDPDT toggle switch for PTT functionSTDT toggle switch for on/off9 volt PP3 batteryNo call tone facilityPCB potted but switches vulnerableDiecast box, no gasket, earth connectionLine connection as flying lead with croc clip

  • The 1988 version (sort of)

  • What happened in practice?Turned on by accident flat batteryNo LED turned off by accidentToggle switches snappedStored damp or with water inside boxCorrosion of wires / switchesNo way to get the attention of called partySpeech level fades as battery drainsPP3s not easy to get in a hurry

  • Nigel Lovell versionBetter box and construction standardHigher line impedanceLED 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 50pSoftware seen as an asset not a riskDC-DC power supply chipsBattery technology advancesThe iPod generation grow up

  • Updating the phone specSingle SPST push-button interface3xAA alkaline to 12V DC-DC step-upMicroprocessor for:Analysing push-button gesturesPower on/off function, low battery warningLED signallingPTT functionTone generationUpgradeable software

  • RuggedizationBrand new military spec 4T earpiecesDiecast box with a gasketIP68 push-button not toggle switchesScrew terminal post for line connectionCroc clip lead as an accessoryCircuit and switch wiring potted3xAA Battery holder replaceable

  • The development version

  • Push Button3-second push to power it upOnce running:Push and hold to talk, as per normalDouble-click to send a call toneClick or timeout to end call toneQuad-click to power off

  • Tone GenerationPower on/off soundWarbling call toneRoger bleep after a transmissionShort bleeps for low battery warningOnce a minute?

  • LED functionsIntermittent flash while turned onEvery 10 secs?

  • 2009 PrototypePIC12F629 with 6 I/O lines in a DIL8 deviceGood for 2.5 to 5.0 volts, in-circuit programmableMAX761 converts 3xAAs to 12 voltsStarts up at 2.5V, low battery logic output to uPOne push-button switchRelay instead of the DPDT toggle switchDiecast box with gasketNATO specification tropicalized 4T earpieceAudio circuit as per Nigel LovellScrew terminal post for line connection