For applications where the detection of motiolesss human occupancy becomes necessary in such scenarios a conventional PIR can become useless, and might require some external arrangement for upgrading itself.
In our previous article we learned about the innovative concept which could be applied for enabling a conventional PIR module to detect even static or stationary human occupancy, over a given premise.
We learned that instead of needing the target to be in motion, the PIR module can be itself be moved over a given radius for implementing the desired static target detection.
In this article we learn regarding a simple circuit mechanism which can be used with a PIR mounted over a small DC motor for the proposed oscillations.
The system basically requires a PWM controlled speed determination and a flip flop changeover for the motor. The following diagram shows how these features can be attributed to the PIR motor with the help of a simple circuit:
R1, R4 = 10K
R2 = 47 OHMS
P1 = 100K POT
D1, D2 = 1N4148
D3 = MUR1560
C1,C2 = 0.1uF/100V
Z1 = 15V, 1/2 WATT
Q1 = IRF540
Q2 = BC547
N1---N6 = IC MM74C14
DPDT = DPST SWITCH OR DPDT RELAY
R3, C3 to be determined by some trial and error
The shown circuit utilizes a single IC HEF40106 hex inverting schmitt gate IC which includes 6 inverter NOT gates.
Gates N1 and N2 are configured to produce an adjustable PWM output which is fed to the gates N4, N5, N6 forming the buffers.
The common output from these buffer gates is terminated to the gate of a motor driver mosfet.
The PWM content is set with the help of P1, which is finally applied to the connected motor via a set of DPDT relay contacts.
These relay contacts determine the direction of the motor movement (clockwise or anticlockwise).
This flip flop DPDT relay contacts is controlled by an astable timer configured around the gate N3, wherein the capacitor C3/R3 determines at what rate the relay needs to changeover in order to allow the motor to change its rotational direction consistently.
The above design allows the motor to execute the required slow to and fro oscillating movement across a given radial zone.
C3 may be selected to initiate the changeover after every 5 to 6 seconds, and the PWm may be adjusted to enable an extremely sluggish motor movement, because it just needs to ensure that the slots of the PIR cross over the IR signals of the target in a timely manner.
However since the motor operation is slow, the output from the PIR will need to be sustained through a delay OFF timer so that the connected load does not switch OFF and ON while the motor movement alternately cuts through the IR lines from the human occupancy.
The following delay timer circuit stage can be used which makes sure that each time the PIR output produces the sensed pulse, the delay from the timer is extended for 5 to 10 seconds and the connected load is never interrupted during the process.
In the above set up we can see the motor which receives its electrical drive supply from the PWM/flip flop stage as discussed in the previous paragraph.
The spindle of the motor can be seen coupled with a horizontal shaft over which the PIR is clamped, such that when the motor moves, the PIR goes through a correspondingly changing radial to and fro motion.
While the above PIR motion is induced, the IR signals from a stationary target in the zone is detected in the form of short alternate pulses, which are generated at the output pin of the PIR indicated with the blue wire.
These pulses are applied across the 1000uF capacitor which charges up with each pulse and makes sure that the BC547 is kept in the conducting mode without an interruption during the process.
The relay driver comprising of the BC557 stage responds to the above stable signal from the BC547 collector and in turn keeps the relay ON, as long as the PIR keeps detecting a human presence.
The relay load thus stays activated continuously due to presence of a stationary human being in the area.
However in case the human occupancy is removed or when the target moves away from the zone, the delay timer stage keeps the relay and the load activated for the stipulated 5 to 10 seconds after which it shuts off permanently, until the zone is yet again captured by a potential IR emanating source.