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SX Specific RS-485 IO

Ruben Jönsson [rubenj at] says:

I have built an RS485 master/slave networked temperature measurement system were each RS485 node can connect to up to 32 DS18S20 devices on a 1-wire network.

The system is used for measuring temperatures on grain at different heights in a grain bin. The temp sensors are inside a cable that is hanging from the ceiling in the bin. Each cable is connected to one RS485 node.

The network is connected to a PC which displays a physical layout of the site (could be a picture or a scanned blueprint) with temperature values overlayed on the image at different colors depending on alarm and warning levels.

The board for the RS485 node is equiped with 1 SX18 processor at 4MHz, 1 24LC16 EEPROM for storing the 1-wire device addresses of each sensor connected to this node (the addresses are automatically scanned and detected with a ROM search upon power up), the 485 circuitry (2400bps, half duplex), interface circuitry for the 1-wire, 2 BCD switches to set the address of the node and 2 leds for status indication.

I have also done a version of this board that is a stand alone hand held battery operated unit with an LCD and two buttons. This is limited to cables with max 14 1-wire tempsensors.

I have used the EEPROM in the 1820 sensor to store an index number of the physical location of the sensor on the 1-wire network in the cable. When the device address is found during the ROM search I know at which height level this sensor is located in this cable.

Ruben Jönsson
AB Liros Elektronik
Box 9124, 200 39 Malmö, Sweden
TEL INT +46 40142078
FAX INT +46 40947388


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