The L1 coil is formed by 4 turns of wire 20 in the form of 0.5 to 0.6 cm without core. The circuit is from an 80's documentation. The range reaches a few tens of meters.
This circuit was found in a 1998 documentation. It is an alarm that uses common components that...
This band rejector filter, which uses the 741 again, prevents signals of a certain frequency, in...
The amplifier shown in figure 2 is based on the MAX9715 integrated circuit from Maxim...