Variable Interval Beeper (ART131E)

With some improvements, the 4093 oscillator can be altered to produce constant-duration pulses in any frequency range, and the frequency range can be adjusted by a simple potentiometer.

The circuit we show here provides an example of how to do that. Our beeper produces short (or long) pulses in a rate from about 3 or 4 per second to one per 3 or 4 seconds.

The tone also can be adjusted in a wide range of frequencies from 100 to 1,000 Hz.

The operation of the circuit is easy to explain. ICl-a is connected as an inverter and will oscillate as described in other articles in this site.

When power is on, C1 charges through R3, and thus the high output of this gate triggers on the second oscillator (IC1-b).

During C1 charge, a tone is produced. When Vp is reached in C3, IC1-a output goes low, and then the IC 1-b oscillator stops.

C1 begins to discharge via R1, R2, and D1 until Vn is reached. Then, the IC1-a output goes high again, and a new cycle begins.

Note that C1 charges through D2 and R3 and discharges through

R1, R2, and D2. Thus, as R1 controls the interval between the output high pulses, R3 determines their duration (see Fig. 1).

Figure 1 – Wave shape for the signals produced by the circuit

Potentiometer R4 adjusts tone frequency, and the output transducer is a piezoelectric device or a crystal earphone. R3 can be altered for shorter or longer pulses in the range between 100 kg and 1 Mohm (audio pulses).

A schematic diagram of the beeper is given in Fig. 2.

Figure 2 – Schematic diagram for the device

By replacing X1 with a 10,000 ohm potentiometer, you can convert this beeper into a variable duty cycle audio generator.