Add external temperature sensors to your RMS unit.

All of our remote site monitoring boards come equipped with an onboard LM75 temperature sensor that provides ambient temperature readings in the vicinity of the RMS board. But what if you need to monitor the temperature outside your equipment building, or in other areas? What if you need to monitor several temperature sensors at the same time?

The fellows at iButtonLink make great inexpensive low powered 1-wire temperature sensors.

The aim of this project is to show you how to use the USB port on the RMS ( remote monitoring system ) to monitor several temperature sensors and view the output on a web page.

The first thing you will need is one LinkUSB 1-Wire interface shown below. The LinkUSB™ is an advanced intelligent USB 2.0 full speed 1-Wire® interface. The LinkUSB has been designed to operate reliably on long or short 1-Wire busses. The LinkUSB interface allows you to plug in one or more temperature sensors.

LinkUSB 1-wire interface.

For a single external temperature sensor, you will need a T-Probe shown below. The T-Probe comes with either 10 or 25 feet of cable, and has a -55C to +125C temperature sensor at the end. This is fully rated for outdoor use.

T-Probe temperature sensor.

For more than one temperature sensor, you can daisy chain several temperature sensors together using standard cat-5 cable. Below is a picture of the T-Sense temperature sensor. The T-Sense temperature sensor houses a DS18B20 temperature chip and has an RJ-45 jack on each end. This sensor is for indoor use only.

Below is a screenshot of the RMS-200 remote monitoring board displaying output of one indoor T-Sense module and one outdoor T-Probe temperature sensor. The temperature gauges are updated every 60 seconds.

The download zip file below contains all of the files needed to display the temperature gauges. Simply download the files and extract them to your computer. With FTP, upload the files to the RMS board at /data/custom/. Go to the RMS setup area and add a custom device. In the "path to custom file" box, enter: custom/linkusb.php and click the OK button. A LinkUSB icon will be displayed in the left navbar as shown above.

Make the linkusbd daemon executable by typing on the command line: chmod 755 /data/custom/linkusbd

Start the linkusbd daemon by typing linkusbd on the command line. When the linkusbd daemon is running it will create the list of 1-wire temperature sensors found and put them in the /tmp/tempsensors.dat file.

Note: when started, the linkusbd daemon will search for a configuration file /etc/linkusbd.conf. If found, the linkusbd daemon will use the device listed in the config file as the device to poll temperature information from. If the /etc/linkusbd.conf is not found, the linkusbd daemon will use /dev/ttyUSB0 as the device to poll temperature information from. To make the linkusbd daemon program start on boot, add /data/custom/linkusbd to the /etc/startup.sh file.

The linkusb.php file is set for only two external temperature sensors. To add more than two sensors, you will have to edit the linkusb.php file. Follow the comments in the file for an idea on what to do.

Link USB files

This concludes the temperature sensor project. We can now remotely monitor the temperature inside and outside our equipment building from the comfort of home or at the office with the RMS remote site monitoring board.