Magno-Sniffer (Magnetic Sniffer Probe Whistler Thing Using A Hall Effect Sensor)

Step 4 Parts

Linear Hall Sensor - Hall things come in 2 main types:

• digital/switching/switch (on or off) or
• linear/analog/sensor (variable voltage).

We want a SENSOR. The part I used is no longer made, so I would try an Allegro Microsystems A1301 (A1301EUA-T)
http://www.allegromicro.com/sf/1301/
Ask for some free samples. But even if you have to buy some, they're pretty cheap. Like from Digikey.

CMOS 555 timer chip - The good ol' 555 timer in CMOS. Has to be the CMOS version. Like Radio Shack's TLC555/TLC555CP LinCMOS Timer (8-Pin DIP) 276-1718.

Some R's and C's - see schematic for values of the resistors and capacitors. Not real critical.

Piezo Speaker - NOT a piezo BUZZER or SIREN, they have their own oscillator. Give them DC power and they whistle on their own. Their specs will say something like "9VDC power". NO. No good.
We want a SPEAKER or TRANSDUCER or ELEMENT or SOMETHING LIKE THAT. With just the piezo cookie in there. Like Radio Shack's Piezo Element 273-073.

Voltage Regulator - In goes 9V. Out comes 5V. With a couple capacitors on it to keep it stable. Like Radio Shack's +5V Fixed-Voltage Regulator 7805 276-1770. Mine's in a different package, but the guts are the same.

9V Battery, battery clip, switch, wire, tongue depressor, hot glue.