Elm Electronics – Circuits for the Hobbyist

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Example Application

ELM412

Output Waveforms

4 of 4

ELM412DSB

Operation of the ELM412 is straightforward,

requiring little explanation. Typically the resonant

frequency of the piezo element is determined, and

pins 2, 3 and 4 are connected for this frequency. In

the circuit of Figure 3, the frequency has been set for

2400Hz. A single bit from a control circuit is then

used to turn the buzzer on and off.

The 2.2K

Ω resistor shown in the circuit serves

two purposes. One is to provide a current limit for the

ELM412 as it tries to rapidly change the piezo

voltage (the piezo is like a large capacitor), and the

other is to simply limit the output loudness.

The only other detail in Figure 3 is the customary

0.01µF capacitor for supply decoupling. It’s always

good practice to add one, although it’s often not

essential.

Control Bit from the

Microprocessor

(1=on, 0=off)

0.01µF

+5V

1

2

3

4

8

7

6

5

Piezo

Element

2.2K

Ω

Figure 3.

Out1

Enable

Out2

Out1 - Out2

The output waveforms are generated as long as

the enable input remains high. When brought low,

the current cycle completes before the output

ceases.

Figure 2.