DIY Instruments for Amateur Space

Chapter 10. Protocols

A sensor just returns a signal, typically a voltage level or a digital series of pulses that encode a data number. If the latter, your sensor may be analog, returning a voltage that must be converted by your satellite’s CPU. Or it may be digital, requiring you to listen at the appropriate clock rate to the correct input line in order to query and catch the signal.

Different sensor protocols—I2C (sometimes called 2-wire), TTL (serial pins), SPI, CAN, UART/serial/RS232 (asynchronous, requiring aligned clocks on both sides), and one-wire—all have different properties. In terms of readout speeds, the protocols, from fastest to slowest (in 8-bit bytes per second) are: SPI, I2C, parallel, serial, one-wire. In terms of complexity, ...