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This is an On Air indicator , ie an indicator circuit dr RF transmission , very simple and useful for those who like RF . This circuit detects the RF output using a visual indicator , but with some modifications , the LED may be replaced by a relay or any other system that want to trigger when the transmitter is switched on. The output of the transmitter or other RF generator must be connected to this RF input circuit.   Simple Circuit indication for RF Output Transmitters List of components Resistor R1 560Ω eighth Capacitor C1 330pF disc C2 Capacitor 0.1μF disc Diode D1 1N34 or 1N60 D2 LED Transistor Q1 2N3904 or equivalent  If you liked this article,Take a few Seconds to Share this and leave comments

Idealy if you have a combustion heater in your home, there should be some means of monitoring the air quality. This is where the Air Quality Monitor comes in, it measures both carbon dioxide and carbon monoxide levels, and displays the results on LED bargraphs. If the concentration of either of these gases rises above a preset level, a loud alarm will sound, which means that you should turn off the heater and open the room up to fresh air. Each bargraph comprises eight LEDs that light invidually to show eight distinct levels. In between values are displaed by lighting two adjacent LEDs. This gives a total of 15 levels that can be displayed. The four lower LEDs are green, followed by two orange and then two red LEDs. An automatic dimming circuit ensures that the LED displays are not too bright at night. In addition, the alarm sounds if any of the top three LEDs light in either display. There are three alarm levels: Main alarm sounds if the top LED lights. This consists of a 64ms-long 4...