Esbus - a sensor bus based on the SPI serial interface

A local sensor bus for transmitting data from several digital smart sensors to an Internet interface was tested. The master/slave type bus is based on the three-wire SPI (serial peripheral interface) bus, which is built into most microcontrollers. At the sensor end, after A/D conversion of the analog sensor signals and further processing of the digitized data, the data is formatted into standard 8-byte ASCII code, which can be read directly by any computer. A header indicates the type of sensor data, for example, TC123.45 for a temperature sensor reading 123.45/spl deg/C. The data is in the form of an email so the following Internet interface (TCP/IP) only retransmits the data to the requesting browser where it is displayed in the same format as any email The Esbus format consists of an 8-byte request from the master followed by 32-byte response from the selected slave. The response is subdivided into an 8-byte header, which identifies the sensor and channel number, and three sets of 8-byte sensor data, as described above. In order to adapt the SPI an addressable network, the data output driver is converted to open collector. The paper will describe the I/O circuits, waveform/timing, and data formats for a specific smart sensor (temperature, humidity, illumination).