Temperature Sensor Signals Its Physical Location In A Crowd

The DS28EA00 digital temperature sensor from Dallas Semiconductor uses a new chain-mode protocol signal to quickly and automatically ascertain the physical locations of individual sensors in applications where multiple sensors are connected to a common line. The device operates over the company’s 1-Wire interface that delivers power and communication over a single connection, allowing multiple sensors to be placed on the line and operated independently. This arrangement minimizes wiring complexity and associated costs in applications that require accurate multipoint digital temperature measurements.

The DS28EA00 measures temperature over the −40°C to 85°C range. Factory calibration in a liquid bath ensures a worst-case conversion error of ±0.5°C within an ambient-measurement range of −10°C to 85°C. Worst-case conversion error from −40°C to −10°C is ±2.0°C. Device temperature sensing and digitization is produced from the differential V_BE output of a matched-npn transistor pair and a first-order sigma-delta analog-to-digital converter. Conversion resolution is user-programmable with 9-bit to 12-bit options.

All 1-Wire devices have a unique 64-bit internal serial number that is used in a multi-drop environment to poll specific devices for temperature results. But the DS28EA00 is the first of its kind to allow users to determine the physical locations of the multiple sensors, employing a chain-mode command set and two signal pins for daisy-chaining multi-dropped devices. A 1-Wire host controller uses the chain-mode command protocol to learn the 64-bit serial number of each part in the chain, starting with the first device on the line and proceeding sequentially. This sequence knowledge is directly linked to the physical location of each device. The daisy-chain signal pins can also be used as 5-V, 4-mA general-purpose IO to control LED indicators or other I/O signaling. The DS28EA00 comes in an 8-pin microSOP package.