Most of the Soldering iron Tips or Bits now available are Copper core surrounded by Iron . It is coated with Nickel or Chromium to prevent the sticking of solder. If we are switched on the soldering iron for long period, the excess heat may damage it permanently. If the soldering work is intermittent, it is ideal to keep the tip half warm. This circuit performs this function. It has a switch and if it is in the Off position, the soldering iron tip remains half warm and if the switch is in the On position, within seconds, it will become fully heated. Don’t be confused. Not a large circuit, but a single diode is sufficient.
This simple circuit performs multi function. It always monitor the Telephone lines and see whether there is any misuse and gives LED indication if it occurs. It gives indications like Phone ON hook state, Off hook state, dialing etc. It is ideal as a tester to see whether the lines are available or not , modem in use etc. It needs no external power and uses the voltage from telephone lines. Two LEDs and a single resistor will make this circuit. You can fix it in the telephone junction box. Make and invite your friends to see your work.