This is the first of a series of posts on creating a wireless remote control for the Zoom H2n audio recorder by using an Android mobile phone (with bluetooth) and a bluetooth serial module to interface to the recorder itself.
A number of the Zoom audio recorders have a 2.5mm TRRS jack socket for use with a custom wired remote control. A number of people have documented their efforts to create their own alternatives and have largely decoded the serial protocol between the control and the recorder. Here are links to some of them:
However, in outline, there is a bidirectional 8-bit asynchronous serial interface operating at 2400 baud and 3.3V logic levels. The 2.5mm socket is wired as follows:
- Tip: RX
- Next Ring: TX
- Next Ring: Ground
- Sleeve: 3.3V power (out)
Although the recorder supplies 3.3V power, it's not capable of supplying much current, certainly not enough for a wireless link, so regrettably the wireless interface needs its own power source. The communication protocol was clearly designed by an electrical engineer: it consists of key-down and key-up events being sent to the recorder to signal the press and release of buttons on the physical remote control and an encoded status byte being sent to the remote control to illuminate status LEDs (such as recording-in-progress and level indicators). There is an initial handshake to establish the connection of the remote control.
Two subsequent posts will describe the hardware and the software.
The software is written using the Xamarin tools for Android and can be downloaded from GitHub.
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