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About
Some years ago when I got my first Raspberry Pi, I stumbled over a Project in the German Raspberry Pi forum, called “batteriebetriebene Funksensoren” – translated “battery operated wireless sensors”. Some people, inspired by Nathan Chantrell’s work , developed two PCB’s. One is called the “TinyRX4”, designed to fit directly on top of the GPIO pin header of the Raspberry Pi.
The other board is called “TinyTX4” and is based on Nathan Chantrell’s “TinyTx3”. Unfortunately I noticed the existence of these boards only after they were already finished, and it was too late to influence the board layout to bring in my RF expertise. Over time more and more contributors stepped out of the project, so I took on the challenge and started my own development.
The TinyTx and TinyRx boards are typical “Maker” boards. They basically work, they fulfill their purpose, but the maker has to put in a lot of thought, time and additional material until a sensor finally works: What kind of housing is suitable? What kind of batteries to use? Where to put the batteries? Should I add a reset button and a status-LED? How to accommodate the antenna? Where to connect the sensor module? At the end I decided to develop a wireless sensor from bottom up.
Step 1: estimate required real estate of the PCB and find a housing to fit the PCB in.
Step 2: the wireless protocol. Transmitting data in ASCII format is extremely redundant, but the redundancy is inefficient. Data can be transmitted far more efficient in binary format by adding parity bits so that transmission errors can be detected (Forward Error Correction, FEC). Additionally wireless transmissions are susceptible to eavesdropping, can easily be recorded and reproduced. Since the range of the transmission can be quite far, sophisticated encryption is mandatory.
Step 3: current consumption. Obviously, there was a lot of potential, in sleep mode as well as in active mode.
Step 4: PCB layout – efficient regarding the used components and the real estate. Optimized for RF performance. Create a large ground pad for the antenna.
Step 5: Simplicity and a certain grade of manufacturability.