The circuit shown in figure 1 generates an intermittent tone in a piezoelectric transducer when the touch sensor is activated. The frequency of the tone is basically given by R2, which can have values between 10 k and 100 k ohms. It will be interesting to determine the value that produces the highest volume sound in the transducer, as many of them have their maximum performance at a resonance frequency around 4 kHz. The flashing depends on R3 and C2, which can also be changed over a good range of values. The ceramic transducer provides good audio power for applications powered by batteries or 9V batteries, as it has low consumption. However, for applications where greater power is required, or where the reader wishes to use a speaker, the power steps in figure 2 can be used. For power supply above 9 V, the transistor must be equipped with a heat radiator. The touch sensor consists of two separate metal plates, which must be touched simultaneously.
