The circuit diagram is quite simple. I have powered my circuit with 4 AA batteries that gives 6 V supply.
A diode is used in series to drop the voltage down to 5.4 V as the operating voltage for the PIC microcontroller should be below 5.5 V. Besides, the diode also provides the protection to the circuit in case of reverse polarity of the power supply. I have tested the circuit with NI-MH rechargeable batteries (that gives 4.8 V) and it worked, but I recommend to use the alkaline batteries (1.5 V each) for better performance. You can also use a 9 V battery but then you need a LM7805 regulator IC in your circuit.

The output of the PIR sensor module is monitored through GP5 (pin 2) of PIC12F635. When the motion is sensed, this output is high at about 3.3 V (my sensor module has a 3.3V regulator IC on board). You could still use this voltage as a valid logic high for PIC12F635, but I preferred to use this voltage to drive the base of an NPN transistor (BC547) so that at the collector we will have the full swing of the logic voltages. Now, the microcontroller monitors the voltage at the collector of the transistor. During the normal condition, the transistor is cut off, and the collector output is at logic high (+5 V). When the motion is sensed, the high output from the sensor module saturates the transistor and the voltage at the collector drops down to logic low. The jumper selection for trigger is at H position, so the sensor output will remain active as long as the motion exists. Note that the PIC12F635 microcontroller uses the internal clock oscillator at 4.0 MHz. The MCLR function is disabled and WDT is OFF in this project.

Leave a Comment

Your email address will not be published. Required fields are marked *