Play it Cool: Solving Thermal Problems, Page 2

On-Demand Reading

Once I had the entire system up and running, I found one thing was missing-temperature reporting on demand. Although I spent most of my time on a computer of one type or another, I found it inconvenient to pull up a Web page or otherwise access the current data. After all, I had the audio system set up to be called upon at any time; I just needed a method to call it.

Contrary to my digital roots, I decided an analog solution would be best-put a physical button on my desktop, and I could push it anytime to hear the current temperature.

The Basics

I decided to use the extra available serial port on the sensor machine for my switch. A typical serial port leaves the request to send (RTS) signal high-which is what I decided to use to power my switch. The return signal would be sent back via the data set ready (DSR) line. All I had to do was rig a switch between the RTS pin (4) and DSR pin (6). When the switch was pressed, the power from the RTS pin would flow back through the DSR pin. A script on the system would monitor the DSR signal and fire off the audio script when it detected the signal high.

The Equipment

A visit to the local Radio Shack netted the required hardware, shown in Table 1.

Table 1: Hardware for the analog switch

Part	Radio Shack Reference Page
Momentary switch	http://www.radioshack.com/product/index.jsp?productId=2062496
25-pin D-sub connector	http://www.radioshack.com/product/index.jsp?productId=2103240
Project box	http://www.radioshack.com/product/index.jsp?productId=2062279

I already had a 9-to-25-pin serial cable (the reason I went with a 25-pin connector for my project), assorted wire, a soldering iron, and a Dremel.

Building the Switch

Building the switch itself was straightforward:

1. Solder wires between pins 4 and 6 on the D-sub connector and the contacts on the momentary switch.
2. Dremel out a slot in the project box for the D-sub connector.
3. Drill a hole in the other side of the project box for the momentary switch (button).
4. Mount the pieces in the project box and connect it to the computer.

Figures 1 through 4 show the completed switch.

Figure 1: The inside of the project box.

Figure 2: The momentary switch (button) mounts on the front of the box.

Figure 3: The D-sub connector mounts on the back of the box.

Figure 4: The switch sits nearby, where I can press it whenever I like.