The Phone Radio Interface is a device designed to provide an audio interface between a smart phone and a radio for use in digital modes. This is done through:
- Capacitive isolation: preventing ground loops
- Trimmer potentiometers to control audio levels to both the phone microphone input and radio input
- PTT control by grounding PTT during TX, based on the presence of audio out from the phone
- Powered by the “Plug-in Power Supply System”, or with a lower R10 value, compatable with iDevice microphone power
The cost of this device is currently A$12 or US$12 for a printed circuit board, or A$25 or US$25 for a board plus components. Purchasers need to provide cables at both the radio and phone sides.
Most components are surface mount technology, but are larger sizes: 1206 and 0805. With good eyesight and reasonably steady hands, soldering these components can be done without the aid of a magnifying glass. There are thru-hole technology transistors, diodes and potentiometers.
Discussion about this and other devices by Wayne VK3WAM can be made in Yahoo Groups at:
Note that R10 requires about 4.7K to cause a 600 uA current draw for iDevices. Most other devices should be compatible with the “Plug-in Power Supply System” for mono microphones, and for these devices, R10 should be around 12K. Samsung Galaxy S2 devices appear to be compatible with the “Plug-in Power Supply System”.