Beeper & Buzzer

An AC millivoltmeter - calibrated in dB - with a range of 30V down to 3mV full scale (80dB range) would be extremely useful. Attach a microphone (electret mic capsules are quite good), and you have a relative sound level meter, even better if you have some way of calibration. The meter presented here has a very wide frequency range, and uses a switched attenuator for range adjustment. The attenuator uses the 30-10-3 sequence, which provides 10dB steps between ranges. The standard attenuator provides an input impedance of over 2M Ohms,

If you can't hear your doorbell when you are in your basement try this circuit. This circuit takes advantage of the 24vac power source located near the furnace. Using a simple current transformer technique, the circuit sounds a beeper whenever the main door chime is activated.

BASEMENT BEEPER TURNS ON WHEN DOOR CHIME IS ACTIVATED

This circuit provides an audible and visual low voltage warning for 12V battery powered devices. When the battery voltage is above the set point (typically 11V), the circuit is idle. If the battery voltage should fall below the set point, the LED will light and the speaker will emit a periodic beeping sound to warn of the impending loss of power. The circuit was designed for monitoring solar systems, but it could also be useful for automotive and other 12V applications.

This circuit produces the sound of a beeper like the one in pagers which produces a "beep-beep" sound. Basically the circuit consists of a 555 timer oscillator which is turned ON and OFF periodically. The first IC(left) oscillates at about 1Hz. The second IC is turned ON and OFF by the first IC. The first IC determines how fast the second IC is turned ON/OFF and second IC determines the tone of the final output.

This box is a portable “transfer standard” to maintain and carry with you a ‘local’ time signal of 59 short beeps (pips) plus a long 0.4 sec beeeeep on the full minute. At the start of the job, the box is started by manually synchronising it “by ear” with a reputable time signal (GPS, WWV/H, or Telstra 1194 on a fixed landline telephone). The box then keeps bleeping, can be taken to an observation site, and can be used there for an hour or so, before the time slowly ‘drifts’ too far out of calibration.

Three circuit options Can be synchronized to Christmas tree flashing lights This circuit generates a dual-tone bells ringing similar to most door-bell units. It can be used in many applications other than door-bell. In the Notes below several options will be given in order to suit different needs.

P1 is of experimental value. Start with 220 Ohms or so and modify to suit your needs. The transistor is a general purpose kind and is not critical, almost any PNP type will work. L1 is a bell-transformer which is usually already present in the house. If you wish, you could use a battery instead of the bell transformer. Just hookup a 9-volt battery (or wall adapter)to points 'A' and 'B' (A=+) the diode (D1) is to protect the circuit from accidental polarity reversal and is optional, but required as a rectifier for use with the bell transformer.

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When wired into a car’s indicator light panel, this circuit will turn on a loud beeper when the “check engine” light turns on.