Nuts & Volts - February 2006

Monitor Indoor/Outdoor Temperature and Relative Humidity

AUTHOR BIO

■ Charles Irwin is a retired engineer and has worked for ITT Worldcommunications, AT&T, and Western Union over a period of 30 years. He holds an Extra Class Ham Radio License (NO2K) and has been licensed since 1974, receiving his first Amateur Radio License from the German Bundespost (DJ0HZ). Irwin has been homebrewing electronic projects since he was 12 years old. He may be contacted at chuck irwin43@netzero.net

If you would like to send your PIC to Charles and have him program it for you, email him for further information.

1N914 or equiv

Using the Monitor

The monitor is simple to use. Pressing the push button activates the unit for approximately one minute and then shuts off automatically. The current drain while the unit is displaying information is about 6 miliamps. When the unit is off, the only current drain is from the CD4011 quad Nand gate, and that was so low I could not even measure it (less than 0.1 microamp).

The batteries should last as long as their normal shelf life provided the LCD backlight is not used continuously. It draws approximately 100 miliamps. It is quite easy to read the display in normal light; the backlight is only necessary in the dark. The display on the LCD is as follows:

71.6F 22.0C 58.5% 059.7F 15.4C 76.3%

The top row indicates conditions from the monitor’s internal SHT15 sensor and the bottom row indicates conditions from the monitor’s remote SHT15 sensor. The bottom row incorporates an extra digit for the F display, since outside temperatures may go over 100 degrees.