In Reply to: principle behind this voltage detector posted by janet on 02/23/03 at 10:38 AM:
When the zener (7.5 volts) conducts, q1 is turned on and q2 is turned off, causing LED1 to go out. There is a problem with that circuit: There is no current limit for LED1. There should be a resistor in series.
1. Infrared is light below the frequency of red light. Ultrasonic is sound above the range of human hearing. RF is radio frequency and may extend from 10kHz to light frequency.
2. HF extends from 3 mHz to 30 mHz. VHF extends from 30 mHz to 300 mHz.
3. Yes, but there are 4 radio control channels in the CB band (26.96-27.23 mHz). Using two of those will make the antenna more efficient. You can look up the frequencies at www.fcc.gov.