6/17

PIR (PASSIVE INFRARED) DETECTOR USING ST7FLITE05/09/SUPERLITE

Figure 3. Conventional PIR detector

1.6 ADVANTAGES OF ST7LITE PIR (COMPARED TO CONVENTIONAL DESIGN)

1. Transistors are used instead of Op-Amps for amplification. This is a low cost solution.

2. Internal RC oscillator of ST7Lite is used - No need for external oscillator.

3. Calibration of internal RC using engineering calibration values available in flash, for gener-

1.7 FEATURES

1.7.1 Tampering detection

An alarm can be switched on if anybody tries to damage/steal the mounted PIR detector. This

can be done by designing the detector in two parts. One part is screwed to the wall and the

second part contains the circuitry and sensor. Removing/stealing one or other part will put the

tamper switch in ON state. This is detected by the microcontroller which switches the alarm

ON. Port PA3 (configured as input pull up) is used to detect tamper. PB2 is a push button

which remains pressed as long as the two parts are attached. When one part is removed, PA3

becomes high and further action (e.g. switching on a alarm) can be taken.

Three pin connector J1 can be used for LED indication or for Relay operation by inserting the

two pin jumper accordingly.

1.7.2 Relay/LED indication option

User can select the LED or relay output for motion indication using three pin connector J2.

LED indication can be used while testing/checking the performance and the relay can be used

in the final application.

Amplifier

Comparator

Output

PIR Sensor

Fresnel lens

IR Radiation

Reference Voltage