Taking Cave Rescue Taking Cave Rescue Telephones ForwardTelephones Forward

Stuart FranceStuart France

WHY?WHY?

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

The 1988 versionThe 1988 version

Second-hand BT “4T” earpieces as mic/spkrSecond-hand BT “4T” earpieces as mic/spkr DPDT toggle switch for PTT functionDPDT toggle switch for PTT function STDT toggle switch for on/offSTDT toggle switch for on/off 9 volt PP3 battery9 volt PP3 battery No call tone facilityNo call tone facility PCB potted but switches vulnerablePCB potted but switches vulnerable Diecast box, no gasket, earth connectionDiecast box, no gasket, earth connection Line connection as flying lead with croc clipLine connection as flying lead with croc clip

The 1988 version (sort The 1988 version (sort of)of)

What happened in practice?What happened in practice?

Turned on by accident Turned on by accident flat battery flat battery No LED No LED turned off by accident turned off by accident Toggle switches snappedToggle switches snapped Stored damp or with water inside boxStored damp or with water inside box Corrosion of wires / switchesCorrosion of wires / switches No way to get the attention of called partyNo way to get the attention of called party Speech level fades as battery drainsSpeech level fades as battery drains PP3’s not easy to get in a hurryPP3’s not easy to get in a hurry

Nigel Lovell versionNigel Lovell version

Better box and construction standardBetter box and construction standard Higher line impedanceHigher line impedance LED flashes once when turned on/offLED flashes once when turned on/off

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

Has anything happened Has anything happened in the past 20 years?in the past 20 years?

Microprocessors costing 50pMicroprocessors costing 50p Software seen as an asset not a riskSoftware seen as an asset not a risk DC-DC power supply chipsDC-DC power supply chips Battery technology advancesBattery technology advances The iPod generation grow upThe iPod generation grow up

Updating the phone specUpdating the phone spec

Single SPST push-button interfaceSingle SPST push-button interface 3xAA alkaline to 12V DC-DC step-up3xAA alkaline to 12V DC-DC step-up Microprocessor for:Microprocessor for:

Analysing push-button gesturesAnalysing push-button gestures Power on/off function, low battery warningPower on/off function, low battery warning LED signallingLED signalling PTT functionPTT function Tone generationTone generation Upgradeable softwareUpgradeable software

RuggedizationRuggedization

Brand new military spec “4T” earpiecesBrand new military spec “4T” earpieces Diecast box with a gasketDiecast box with a gasket IP68 push-button not toggle switchesIP68 push-button not toggle switches Screw terminal post for line connectionScrew terminal post for line connection

Croc clip lead as an accessoryCroc clip lead as an accessory

Circuit and switch wiring pottedCircuit and switch wiring potted 3xAA Battery holder replaceable3xAA Battery holder replaceable

The development versionThe development version

Push ButtonPush Button

3-second push to power it up3-second push to power it up Once running:Once running:

Push and hold to talk, as per normalPush and hold to talk, as per normal Double-click to send a call toneDouble-click to send a call tone

Click or timeout to end call toneClick or timeout to end call tone

Quad-click to power offQuad-click to power off

Tone GenerationTone Generation

Power on/off soundPower on/off sound Warbling call toneWarbling call tone Roger bleep after a transmissionRoger bleep after a transmission Short bleeps for low battery warningShort bleeps for low battery warning

Once a minute?Once a minute?

LED functionsLED functions

Intermittent flash while turned onIntermittent flash while turned on Every 10 secs?Every 10 secs?

2009 Prototype2009 Prototype

PIC12F629 with 6 I/O lines in a DIL8 devicePIC12F629 with 6 I/O lines in a DIL8 device Good for 2.5 to 5.0 volts, in-circuit programmableGood for 2.5 to 5.0 volts, in-circuit programmable

MAX761 converts 3xAAs to 12 voltsMAX761 converts 3xAAs to 12 volts Starts up at 2.5V, low battery logic output to uPStarts up at 2.5V, low battery logic output to uP

One push-button switchOne push-button switch Relay instead of the DPDT toggle switchRelay instead of the DPDT toggle switch Diecast box with gasketDiecast box with gasket NATO specification tropicalized 4T earpieceNATO specification tropicalized 4T earpiece Audio circuit as per Nigel LovellAudio circuit as per Nigel Lovell Screw terminal post for line connectionScrew terminal post for line connection