Display a temperature reading on your site

The home page of the iCatcher website features a small panel that shows the current temperature in our Hampshire offices. The process of setting this up is actually very simple and requires very little hardware to achieve.

The hardware

The temperature sensor itself is the RS232 Temperature Sensor available on our CCTV shop. This low cost sensor provides a simple temperature reading over the serial port and requires no configuration or driver installation. Note that many modern PCs do not have serial ports built-in, in which case the USB Temperature Sensor is more suitable. This provides the same temperature readings, but has a built-in USB-to-serial converter allowing it to be connected to modern PCs that don't have a serial port available.

No other hardware is required, except for the obvious PC to run the software and any networking/internet router hardware required to connect with the internet.

The software

We use iCatcher Console for our CCTV and automation systems. The software allows you to set up various controllable devices and sensor inputs including temperature, humidity, and remote signal inputs.

Our installation is configured with the temperature sensor as an input, and is also set to log the temperature readings to a file that can be analysed using the built-in graphing facilities. Our installation is web accessible, which allows us to read the sensor values remotely as per the HTTP API SDK.

Web configuration and coding

Our website uses AJAX web technology to read the sensor values and update the web page. This process uses JavaScript to read the sensor values as XML from our iCatcher Console installation, extract the temperature reading, and then insert HTML onto the web page showing the temperature reading.

Note that there is a security issue that needs to be worked around in order for this to work correctly. AJAX does not permit JavaScript on one site to access XML on another. To work around this we configured the Apache web server (which runs our site) to effectively proxy a URL on the web site through to our CCTV system. Most professional web hosts should allow you to set this configuration, however some of the free providers may not support this.