Before we go to an improved design, here is an unusual circuit using
a PNP (BC 557) transistor. Firstly, PNP transistors do not work as well
as NPN transistors. I would reverse the 4k7
and electret mic as the voltage between base and 0v rail is very small
and the 4k7 is not biasing the transistor - it is not needed! The range will be 50 to 100
metres and the current is about 3mA.
Note: A reader built this circuit. It did not work!!
Try putting the 47p across the coil. The 33p may need to be reduced to 10p.
It is just a BAD design, but a good challenge to see if you can get this type of design to work.
Note: A reader built this circuit. It did not work!!
Try putting the 47p across the coil. The 33p may need to be reduced to 10p.
It is just a BAD design, but a good challenge to see if you can get this type of design to work.
The 22n is not shown. This
is a later addition.
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