Alarm Translator Mini Circuits

This circuit, fenced in a very tiny plastic box, will be placed into a bag or purse. alittle magnet is placed near the reed switch and connected to the hand or the garments of the person carrying the bag by means that of a small twine. If the bag is snatched dead, the magnet looses its contact with the reed switch, SW1 opens, the circuit starts periodical and therefore the speaker system emits a loud alarm sound. A complementary transistor-pair is wired as a high potency generator, directly driving alittle speaker system. Low part-count and 3V battery provide enable a really compact construction.

Parts:

R1 = 330K
R2 = 100R
C1 = 10nF-63V
C2 = 100uF-25V
Q1 = BC547
Q2 = BC327
B1 = 3V Battery or Two AA Cells in Series
SW1 = Read Switch & Small Magnet
SPKR = 8R Loudspeaker (See Notes)


 Notes:

• The loudspeaker can be any type; its dimensions are limited only by the box that will enclose it.
• An on-off switch is unnecessary because the stand-by current drawing is less than 20µA.
• Current consumption when the alarm is sounding is about 100mA.
• If the circuit is used as anti-bag-snatching, SW1 can be replaced by a 3.5mm mono Jack socket and the magnet by a 3.5mm. Mono Jack plugs having its internal leads shorted. The Jack plug will be connected to the tiny cord etc.
• Do not supply this circuit at voltages exceeding 4.5V: it will not work and Q2 could be damaged. In any case a 3V supply is the best compromise.Electronics Circuit Application