Cypress Semiconductor CY8C21534 Especificações descarregar pdf (Página 24)

parameters of the oscillator circuit which change the speed at which the circuit

oscillates. The oscillation comes from what is known as a Capacitive Sensor Relaxation

Oscillator (CSR). Figure 12 shows the circuit layout of the CSR.

Figure 12: Capacitive Sensor Relaxation Oscillator. Taken from Lesher Todd [10].

The circuit consists of a comparator, a switch, and a capacitance that comes from the

layout of the buttons. The capacitor is first charged to a voltage level defined by the

comparator. When that voltage is reached the switch is closed to allow the capacitor to

discharge into ground. The time that it takes to complete this cycle is noted by the use

of a counter. The cycle is repeated and the counter results are compared to one

another. As the capacitance changes due to a user touching the button, the charge

time will grow larger due to the increase in capacitance. The larger charge time can be

seen in the form of a larger counter number. The MCU is programmed in such a way

that as the charge time of the capacitor passes a preset threshold, predefined actions

are triggered. For example, a relay can be connected that will in turn start a motor or a

large bank of lights. Several of the capacitive touch buttons can be implemented on

the PSoC MCU, acting independently of each other, to perform different operations for

the system [11].

Many of the capacitive touch pads designed in projects are based on printed circuit

board layouts. The design is done in specific software so that proper spacing between

capacitive sections of the button can be attained.

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Cypress Semiconductor CY8C21534 Especificações Página 24