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IMPLEMENTATION OF SIGMA-DELTA ADC WITH ST7FLITE05/09

2 REALISATION WITH THE USE OF THE MICROCONTROLLER ST7FLITE05(09)

The practical realisation of the Sigma-Delta converter has been used with our passive infrared

detector. A sensor of passive infrared characterises with a low output voltage (below 10mV)

as well as with a usable range of frequencies from 0,2Hz to 7Hz. Therefore the Sigma-Delta

converter is a perfect solution. It provides an accurate enough conversion of a signal into its

digital form with use of a minimal number of external elements. That means simplicity of con-

struction, relatively low production costs and good using properties.

Figure 3 presents the block diagram of the detector.

Figure 3. ST7FLITE05 interfacing with PIR Sensor

A signal from the sensor passes through the capacitor to the input of the converter. The A/D

converter has been used as a comparator in the microcontroller as well as the source of the

reference voltage. By enabling the internal x8 amplifier, the amplitude of an output signal has

been decreased 20 times to provide correct operation of the amplifier. This allows a decrease

in the resistors’ value span in the same ratio and to increase the operational accuracy of the

A/D converter working as a comparator. Additionally the temperature compensation of sensi-

tivity has been introduced.

Figure 4 shows the work algorithm of the Sigma-Delta converter.

POWER

PB 4

x8

PB 1

ADC

ANALOG

INPUT

PB 0

ANALOG

INPUT

OUTPUT

ST7FLITE05

PA 6

PA 5

PA 4

PA 1

TP

PA 0

CONFIGURATION

PA 7

OUTPUT

SERIAL OUTPUT

LD2980

ELEMENT PIR

REL