Based on a Raspberry Pi, it is a solar-powered radio beacon which transmits signals in regular intervals including live images taken by a small camera.
Since the device will transmit using a simple radio, no wired or cellular coverage is needed, thus it can be a real off-the-grid appliance.
After the camera takes a picture the Raspberry Pi converts the images into an audio signal which be broadcast using slow-scan television (SSTV) transmissions via a radio transceiver.
The design by “hackbp” from Budapest on the Instructables maker website uses a cheap Baofeng handheld radio transceiver – UV-5R. It needs to have PTT control and microphone inputs.
Two connections are required between the Raspberry Pi and the radio.
First, the audio must be routed from the output of the Pi (light blue 3.5mm TRS/Jack socket) to the microphone input of the radio (bigger 3.5mm TRS/Jack socket). This requires two wires and two Jack connectors.
Second, the PTT (Push To Talk) functionality must be controllable by the Pi to switch the radio between transmitting and receiving. This can be toggled on the radio by shorting the grounds of the above mentioned 3.5mm and the other 2.5mm TRS sockets, thus requires an additional, smaller Jack connector.
The connection requires a transistor and a resistor, and a relay was added for stability. The transistor is controlled via its base connected to one of the GPIO (General Purpose Input/Output) pins on the Raspberry Pi. So setting a value to 1 or 0 in software results in the pin being connected to the power supply (3.3V on the Pi) or ground, respectively.
For an OS the design used Raspbian and made use of the raspistill function for the picture-taking operation. Conversion to SSTV modulated sound file used PySSTV and UNIXSSTV. This needed Python, Git and GCC which is present by default on Raspbian.
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