Enough next to your telephone to put a small plastic box, as from the speaker there is a loud voice. The secret here is simple: mounted in the box coil (scheme) “detects” the electrical signals of the phone conversation, coming then a three-stage transistor amplifier with low frequency.
Coil L1 and ULF are linked by a two-meter shielded cable. The sensitivity of the device is adjusted by potentiometer R1.
L1 contains 1250 turns of wire PEL of 0.1—0.15, is wound in several layers on a ferrite rod Ф600 (Ø 10 mm, length 140 mm). The transistors T1, T2 — МП39 — МП42, T3 — МГІ20, TP1 — output transformer from a pocket radio, Гр1 — compact loudspeaker type 0,5 GD-17, GD of 0.5-20.
Recommend to read
“REINS” ON THE BATTERY
No matter how small portable power supply network of the car — the weight is nevertheless solid. Very rare, but it will let you know when the battery it is necessary to remove, transfer,...
HAND PUMP
Well — vital structure on the estate, even if a centralized water supply system. Design it can be any. We have, for example, the popular tube-wells, good bearing rocks occur close....
