The HP Alpha DS20E computer system runs the OpenVMS operating system and has two RS232C serial ports. In order to monitor the health status of the system, a room temperature sensor is connected to the Alpha computer via the serial port. A DCL script then polls the serial port every 5 minutes for the room temperature. The temperature, along with other environmental information, is written to a html page and then transferred to an IIS web server where it can be viewed with a browser.

If an event such as the temperature exceeds a pre-determined alarm setting, an alert message is sent to the OpenView Console(OVO) which is monitored 24-hours. An example of a web page for an Alpha with an alarm condition can be seen here.

The room temperature sensor is a DS18B20 digital thermometer which is interfaced to a PICAXE-08M microcontroller as shown in the schematic below.

Click here : PICAXE code


Power for the circuit is derived from the RTS pin of the serial port. The voltage of this pin is normally at 0V but rises to 9V when the port is initialised with the command:

$ SET TERMINAL/MODEM/NOECHO/SPEED=2400 TTA0:

The resistor network divides the RTS voltage equally and approx 4V is supplied to the PICAXE. The sensor is built into an old serial mouse case with its innards gutted. The circuit is built on a matrix PCB which is shaped to fit into the casing.




The DS18B20 is attached to the PICAXE with standard square board pins and sockets for ease of assembly and future maintenance.


The sensor pokes out of a hole drilled into the upper shell of the casing. It is not glued to the casing as it was found the tension of the bent wires kept it fairly secure in the hole. The assembled mouse sensor looks like this.


This pictures shows the sensor sitting behind the Alpha computer and connected to the serial port. The long mouse cable is actually useful in allowing the mouse to measure the temperature of nearby equipment eg. fan output.