What is it?

This is a populated smd PCB for an interface circuit allowing a modified CM108 USB sound card to interface with a Baofeng Ham Radio. It is primarily used when linking a raspberrypi to a Baofeng BF888s or UV-5R transceiver to make a personal Amateur Radio Hotspot, or APRS Digipeater.

Why did you make it?

I didn't want to cannibalise the radio to interface with a RaspberryPi, so this board allows me to use an old earphone/microphone lead that just plugs into the radio.

What makes it special? Amateur Radio enthusiasts (Hams) are embracing technology to push the boundaries of their hobby. Licensed amateurs view this as necessary to keep their hobby alive. While it is possible to buy a handheld transceiver for anywhere upwards of £20, the cheaper radios, and the conditions of a foundation licence in the UK are limited in power, 5W being typical. This inevitably means the range of these radios is measured in low miles/km. If you are lucky to have a local repeater, that can extend range to maybe tens of miles/km. With a personal 'hotspot', global reach can be achieved!! A hotspot consists typically of a RaspberryPi computer connected to the Internet, and some form of Interface to a low power transceiver. Transmitting on low power (typically 0.5W - 1W) from a cheap handheld to an equally cheap transceiver attached to the PI enables access to global servers able to retransmit world wide.

To provide control from the PI to the hotspot transceiver usually requires a modified USB sound card (CM108) and the output hardwired into the radio. My interface board negates the need to hardwire or modify the hotspot transceiver, instead allowing a modified earphone/microphone lead to be plugged in as normal. This circuit allows the CM108 sound board to activate the COS function on transmit by using a 2N7000 Mosfet as a switch.