Whistle key finder device. Its operation is basically a keychain that responds with a beep-beep sound when we whistle at the right frequency. A miniature electret microphone captures the whistle and sends it to the microphone preamplifier, which consists of a pair of BC548 transistors, to be amplified to the right level before it reaches pin 5 of the PIC12F675.
The timer 0 then counts how many pulses have occurred in a certain time period. This number corresponds to the frequency of the whistle and is compared with the value previously recorded in the EEprom memory of the PIC12F675.
Some commercial devices use a special integrated circuit for this purpose, for example; HK226. The frequency of the sound is fixed, about 1 Khz. In this circuit, we can select the frequency of the whistle. Press the ‘SW_PROG’ button and whistle. When the LED lights up, you can release the button and stop whistling. The whistle is recorded in the internal EEprom memory of the PIC12F675.
Key finder device When we repeat the recorded whistle, a rapid series of beeps should be heard and the LED should flash. The power supply can be provided by a 3-volt CR2032 battery. The 20 mm piezoelectric disk should be glued to the plastic case from its edges.
Attention: Although the program filters the sounds, other sounds in the environment can also trigger the beep-beep sound if they are at the same frequency as the recorded whistle. It is possible to narrow or widen this filtering by changing the settings in the C program.
Note: The PCB drawing of the whistle key finder circuit was drawn with sprint layout 6. It was checked, not tested. The key finder circuit has CCS C source C code, hex code.
Whistling Key Finder Circuit Diagram
source: picsource.com.br/archives/11455/
