Beeps when hears your whistle
A gadget suitable for key-holders, games etc.
The first two inverters contained in IC1 are used as audio amplifiers. IC1A amplifies consistently the signal picked-up by the small electret-microphone and IC1B acts as a band-pass filter, its frequency being centered at about 1.8KHz. The filter is required in order to select a specific frequency, the whistle's one, stopping other frequencies that would cause undesired beeper's operation. IC1C is wired as a Schmitt trigger, squaring the incoming audio signal. IC1D is a 2 second (approx.) monostable driving the a stable formed by IC1E & IC1F. This oscillator generates a 3 to 5Hz square wave feeding Q1 and BZ1, thus providing intermittent beeper's operation.
A gadget suitable for key-holders, games etc.
Circuit diagram:
Parts:
- R1 22K 1/4W Resistor
- R2 10K 1/4W Resistor
- R3 4M7 1/4W Resistor
- R4,R8 100K 1/4W Resistors
- R5 220R 1/4W Resistor
- R6 330K 1/4W Resistor
- R7 47K 1/4W Resistor
- R9 2M2 1/4W Resistor
- R10 1M5 1/4W Resistor
- C1,C5 47nF 63V Polyester or Ceramic Capacitors
- C2,C3 10nF 63V Polyester Capacitors
- C4,C6 1µF 63V Electrolytic Capacitors
- D1,D2 1N4148 75V 150mA Diodes
- IC1 4049 Hex Inverter IC
- Q1 BC337 45V 800mA NPN Transistor
- MIC1 Miniature electret microphone
- BZ1 Piezo sounder (incorporating 3KHz oscillator)
- B1 2.8 or 3V Battery (see notes)
Device purpose:
Some 15 years ago it was common to see small key-holders emitting an intermittent beep for a couple of seconds after its owner whistled. These devices contained a special purpose IC and therefore were not suited to home construction. The present circuit is designed around a general purpose hex-inverter CMos IC and, using miniature components and button clock-type batteries can be enclosed in a matchbox. It is primarily a gadget, but everyone will be able to find suitable applications.Circuit operation:
This device beeps intermittently for approx. two seconds when a person in a range of about 10 meters emits a whistle.The first two inverters contained in IC1 are used as audio amplifiers. IC1A amplifies consistently the signal picked-up by the small electret-microphone and IC1B acts as a band-pass filter, its frequency being centered at about 1.8KHz. The filter is required in order to select a specific frequency, the whistle's one, stopping other frequencies that would cause undesired beeper's operation. IC1C is wired as a Schmitt trigger, squaring the incoming audio signal. IC1D is a 2 second (approx.) monostable driving the a stable formed by IC1E & IC1F. This oscillator generates a 3 to 5Hz square wave feeding Q1 and BZ1, thus providing intermittent beeper's operation.
Notes:
- Power supply range: 2.6 to 3.6 Volts.
- Standing current: 150µA.
- Depending on dimensions of your box, you can choose from a wide variety of battery types:
- 2 x 1.5 V batteries type: AA, AAA, AAAA, button clock-type, photo-camera type & others.
- 2 x 1.4 V mercury batteries, button clock-type.
- 1 x 3 V or 1 x 3.6 V Lithium cells.
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