The following PIR LED lamp circuit was designed by me for one of the followers of this blog Mr.Deepak upon his request.

The circuit is a LED driver which responds to ambient light as well as to the presence of a human, person or intruder, and varies its illumination accordingly, let's know more.

Technical Specifications


"I was looking to drive 20 LEDs of 0.06 watts.
So total Output voltage is 12-17 volts and total current is 0.08 amps
to drive 4 strings of 5 LEDs each
each led is 3.4 volts and 20 mA.
Can you help with this?
Also I would like to have an ambient sensor to switch on and off and a proximity sensor to switch to full brightness if some one approaches and to switch to half or 30% brightness after 30 seconds.
I need this for commercial use. I need a simple cost effective circuit. I have been following the blog and am sure that you know the subject. Please get back to me."

Simulation and Working


The following circuit designed by me hopefully should perform the  functions that's demanded in the above request.

The PIR based sensor will detect the presence of a human by sensing the occupant's body heat and convert it into an electrical triggering pulse which will in turn switch ON an integrated LED lamp module, the lamp will remain illuminated only for so long as the occupant stays in the premise and would shut off as soon the person leaves the area.



Let's try to understand the PIR based LED lamp circuit functioning from the following points:

The IC 555 is configured as a comparator, the LDR and R8 values are compared for generating an appropriate output.

As long as there's enough light over the LDR, pin#2 of the IC remains high and this keeps the output pin#3 of the IC high as well.

The high output at pin#3 keeps the transistor and the LED switched ON, until the ambient light falls below a predetermined value set by P1.

This means during night or in the absence of light the LEDs too get switched OFF.

The upper section is a proximity sensor circuit. The transistors T2 and T3 are configured as high gain amplifier and is able to sense even minute voltages from the PIR sensor.

In the presence of any human or animal in the specified vicinity, the PIR becomes active and triggers T3, which in turn switches ON T2.

T2 instantly shorts R1, such that the supply voltage reaches the LEDs directly instead of via R1.

This situation brightens up the LED illumination, indicating the presence of a passer by (as stated in the request).

The capacitor C1, ensures the LED brightness stays alive for many seconds, even after the PIR is deactivated.

Parts List


R1 = 100 Ohms,
R2,R4 = 100K,
R3,R5, R6 = 10K,
R7 (at IC 555 pin2) = 2M2,
R7 at PIR positive = 10K
R8 = 2M2,
C1 = 470uF/25V
LED resistors = 100 Ohms each,
T1, T3 = BC547,
T2 = BC557,
D1 = 4.7V zener
LDR = any standard type.
PIR sensor = any standard type.
IC1 = 555

Simple PIR Controlled LED Lamp Circuit


The following circuit shows a simple motion sensor which activates the connected LEDs in response to the presence of humans within the specified area.

The LEDs remain switched ON even after the IR source has disappeared from the premise due to the introduction of C1.

The time for which the LEDs remain ON is determined by the product of R4 and C1, which is directly proportional to the time period.

This simplified version of the above circuit was requested by one of the interested readers of this blog.


Parts List for the above circuit:


R4, R5, R6 = 10k
C1 = 100uF/25V
T2 = BC557
T3 = BC547
LED resistors = 100 ohms
D1 = 4.7V zener

Darkness Activated PIR Circuit


The following circuit can be used for automatically detecting human presence, and activating the lights during night time.

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