This circuit was found in Popular Electronics from 1993. The 1458 consists of a double 555. The phone can be a low impedance magnetic or even a piezoelectric capsule. The coil is a telephone pickup type, but it can be improvised by wrapping around 500 to 1000 turns of very fine enameled wire in a small ferrite rod. The power consists of a 9 V battery.
| Clique na imagem para ampliar |
