You need one of these:
Contact me to buy one.
These are the parts to buy.
Modules 2x Arduino Pro Mini eBay 182630720464 £2.15 each 1x GPS (pin order VCC RX TX GND) eBay 152939655666 £10.75 Semiconductors Q1 BC547/8 PTT - not optional :) Q2 BC547/8 only if you want the relay D1 1N4001 RS 628-8931 only if you want the relay DS1 DS18b20 temp sensor eBay 161879382812 £1.25 only if you want temp sensor 1x L7808CV regulator eBay 172377863651 £0.23 wide range -> 7V 3x LED (green, red, or yellow) all optional Capacitors C1 10nF (103) eBay 231179599601 RX audio DC blocking cap C2 100nF (104) eBay 231179599601 TX audio DC blocking cap Cout1 470nF electrolytic RS 711-1677 power smoothing Cin1 220nF electrolytic RS 167-1538 / eBay 221321519025 power smoothing Resistors R1 1k PTT current limiting resistor R2 10k RX audio offset pot divider R3 100k preset eBay 130894545879 £0.184 TX audio level set R4 10k RX audio offset pot divider R5 4.7k Onewire bus vcc-d only if want temp sensor R6 10k beacon button pull-down only if want beacon button R7 18k battery voltage sense PD (VCC to A1) only if want volt sense circuit R8 6.8k battery voltage sense PD (A1 to GND) only if want volt sense circuit R9 150R fix LED current limiting resistor * only if want LED D13 R10 150R TX LED current limiting resistor * only if want LED D9 R11 4.7k relay current limiting resistor * only if want the relay R12 150R spare LED current limiting resistor only if want LED D10 * select appropriate values for the LEDs you use Other U1 G5Q 5v relay RS 841-1420 optional, e.g. drive a fan Screw terminal 3.5mm pitch RS 897-1332 or just solder the wires 2x 12 way female pcb socket eBay 131921173215 £0.21 optional, for the arduinos
The left hand Arduino needs to have the Mobilinkd TNC firmware blown on to it. Like this:
avrdude -c arduino -p m328p -P COM3 -b 57600 -U mobilinkd-473-arduino.hex
The right hand Arduino needs to have this Arduino sketch blown on it – but remember to modify it for your own callsign, at the very least! That sketch is rough and ready, built in a hurry, and doesn’t have extras (temp sensor, battery voltage sampling, relay control) implemented. It also depends on MicroNMEA library which you should be able to find fairly easily.
The PWR port is good for 13.8V- the regulator and capacitor circuit is taken from a battery eliminator designed for a vehicle.
Set TX audio level carefully. It’s touchy. You can do this using the Mobilinkd Windows desktop software, plugged into the left hand Arduino, to activate test tones. That desktop utility isn’t very good, fiddle with it until it works.