Nuts and Volts - August 2010

“Min/Max” temperatures shown on the Hyper Terminal screen are 100 more than their actual values. They are stored on the PIC this way to accommodate negative temperatures on a device that does not normally understand negatives.

The Software

The program for the PIC12F683 is written in PICBASIC PRO. The code (available at www.nutsvolts.com) is well documented and should be fairly easy to follow. You will also note that there are a number of “SEROUT” commands. These send information to the device’s serial port and were used for debugging as they give information on the program’s operation. If more program space is needed for additional modes or features, the serial commands can easily be removed.

■ FIGURE 2. Hyper Terminal screen.

Reading the Temperature

The objectives state that the temperature must be reported in a manner that is easily understood. Being an amateur radio operator, my first inclination was to use Morse Code for the numbers but the thought of teaching the sequence of dots and dashes to my riding comrades convinced me to search for another alternative. The simplest code I could come up with has proven to be easily understood by everyone who sees it.

A temperature report always starts with a rapidly blinking sequence where the LEDs flicker for a half second or so. Next, the number of hundreds of degrees is displayed followed by a short pause, the number of tens, another pause, and the number of ones. The software suppresses the reporting of hundreds of degrees if the temperature is below 100. When reporting numbers of degrees, the LEDs flash at a rate of about 1/3 second on and 1/3 second off. When reporting a zero, they flash on and off much more rapidly. These rates can easily be changed in the software but have worked well throughout a full year of testing.