Simple Automatic Street Light System

A super simple light activated switch circuit is explained here. The circuit can be used for automatically switching ON and switching OFF a particular lamp or group of lamps in response to the varying ambient light levels. The unit once built can be used for switching OFF a lamp when dawn breaks and switching it ON when dusk sets in.

The circuit can be used as an automatic street light controller system or a simple light activated switch.

Let’s try to understand the functioning of this useful yet simple automatic street light circuit and how it is so simple to construct:

Referring to the proposed automatic street light circuit figure we can see a very simple configuration consisting of just a couple transistors and a relay, which forms the basic control part of the circuit.

Of course we cannot forget about the LDR which is the prime sensing component of the circuit.

The transistors are basically arranged such that they both complement each other oppositely, meaning when the left hand side transistor conducts, the right hand side transistor switches OFF and vice versa.

The left hand side transistor T1 is rigged as a voltage comparator using a resistive network. The resistor at the upper arm is the LDR and the lower arm resistor is the preset which is used to set the threshold values or levels.  T2 is arranged as an inverter, and inverts the response received from T1.

Initially, assuming the light level is less, the LDR sustains a high resistance level across it, which does not allow enough current to reach the base of the transistor T1. This allows the potential level at the collector to saturate T2 and consequently the relay remains activated in this condition.

When the light level increases and becomes sufficiently large on the LDR, its resistance level falls, this allows more current to pass through it which eventually reaches the base of T1.

The transistor T1 conducts, pulling its collector potential to ground. This inhibits the conduction of the transistor T2, switching OFF its collector load relay and the connected lamp.

The power supply is a standard transformer, bridge, capacitor network, which supplies a clean DC to the circuit for executing the proposed actions.

The whole circuit can be built over a small piece of vero board and the entire assembly along with the power supply may be housed inside a sturdy little plastic box.

 The LDR must be placed outside the box, meaning its sensing surface should be exposed toward the ambient area from where the light level is required to be sensed.

Care should be taken that the light from the lamps does not in any way reach the LDR, which may result in false switching and oscillations.
Automatic Street Light Circuit
Parts List for the above simple automatic street light circuit system

R1, R2, R3 = 2K2,
VR1 = 10K preset,
C1 = 100uF/25V,
C2 = 10uF/25V,
D1 ---- D6 = 1N4007
T1, T2 = BC547,
Relay = 12 volt, 400 Ohm, SPDT,
LDR = any type with 10K to 47K resistance at ambient light.
Transformer = 0-12V, 200mA


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87 comments

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Anonymous
April 29, 2012 at 10:23 PM delete

hi ..what is the cost of this project?

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Anonymous
September 20, 2012 at 11:34 PM delete

it's not simulating.Please help me

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Anonymous
September 20, 2012 at 11:37 PM delete

please help me to simulate

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September 21, 2012 at 9:57 AM delete

Don't use any software, instead do it in your mind, or even better if you can make it practically.
I have already explained the functioning in the article.

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Ram
December 11, 2012 at 5:59 AM delete

Sir, want to add ldr switch for 6v emergency light. plz suggest simplest way to replace manual switch with ldr

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December 11, 2012 at 12:05 PM delete

What type of LDR switch? A day/night switch or flashlight operated toggle switch???

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Ram
December 11, 2012 at 5:08 PM delete

Day night to automatically off in day for 6v emergency light.

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December 11, 2012 at 8:31 PM delete

One such circuit has been discussed in the following article, third circuit from bottom:

http://homemadecircuitsandschematics.blogspot.in/2011/12/how-to-make-efficient-led-emergency.html

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Anonymous
February 4, 2013 at 7:02 PM delete

dear sir , i am going to make this circuit. instead of outside light i am going use LED near by the LDR. this will operate the relay ?

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February 4, 2013 at 7:46 PM delete

Yes, the LDR and the circuit will respond to all kinds of visible light...

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Anonymous
February 4, 2013 at 9:26 PM delete

ok sir, i will give u feedback. thank u

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Anonymous
February 6, 2013 at 12:16 AM delete

sir , i did the circuit.please tell me setting method and where i can place a led to know relay status.

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February 6, 2013 at 10:03 AM delete

allow light to fall on the LDR, adjust VR1 such that the relay just switches OFF.

Now if you cover the LDR with your hand, the relay should switch ON back.

You can connect an LED across the relay coil with a 1K series resistor.

Do not allow the light from the lamp connected with the relay contacts to fall on the LDR.

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Anonymous
February 7, 2013 at 12:58 AM delete

thank you sir,

* when i switch on the device the relay off condition.

* if i cover with my hand on the LDR the relay switch on.

* after remove my hand from the LDR ,the relay is not off.( if i touch the R3 leg the relay switch off)

please tell me the circuit is right or wrong .




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February 7, 2013 at 10:49 AM delete

The difference between the light and the darkness falling on the LDR should be large, only then it will work properly.

meaning either the light should be more when the LDR is uncovered, or the darkness should be more when its covered.

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Anonymous
February 7, 2013 at 9:40 PM delete

ok sir . i understand. iam using big size LDR only. when i switch on the circuit the realy is in N/C mode. then i cover the LDR the relay goes to N/O mode. after remove my hand from the LDR the relay is not comes to N/C mode. i am using 250ohm relay . please help me solve ..

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February 8, 2013 at 11:46 AM delete

The darkness level should be large, means it must be very dark compared to the light that you are using on the LDR...

relay rating is OK

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February 16, 2013 at 11:07 PM delete

Hi sir please HELP me not used for ic ckt

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Anonymous
February 25, 2013 at 11:42 PM delete

sir,can you please tell me how to connect an LDR between two npn transistors

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February 26, 2013 at 7:45 PM delete

explain your requirement in detail.

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February 26, 2013 at 9:42 PM delete

i am not get the 400ohm relay. what can i do to work it? how can i use 200ohm relay?

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February 27, 2013 at 7:51 AM delete

you may use a 200 ohm relay in place of the shown relay.

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February 27, 2013 at 11:52 AM delete

but my 200ohm relay dose not stop, relay always NC mode.

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February 27, 2013 at 1:08 PM delete

have you connected everything as shown in the diagram??

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February 27, 2013 at 2:51 PM delete

yes sir, i use Transformer 0-12V, 300mA C1 = 100uF/63V,C2 = 10uF/63V

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February 27, 2013 at 8:09 PM delete

What about the LDR, what type have you used?

Did you adjust VR1 correctly?

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March 1, 2013 at 12:00 PM delete

Help me please do not work used for really

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March 7, 2013 at 1:05 PM delete

Sir,


My name is raigon jose and i am from kerala


And i made 1 solar street light with 12 VOLT 100 WATTS panel & 42 ah SMF battery & Lights 1 watt Edisson LED 20 Numbers

( 3 V x 4 ) A pair of 4 Led Series -------- 12 v ( 5 Rows) 20 WATTS Total

I have a problem faced from automatic ldr switching Circuit
LDR SWITCH CIRCUIT Installed in light Dom
LDR is installed inside the light cover
When evening 5 'O Clock the Light will be switch on & morning after 7.30 am will be switch off

When i searched about this problem i got u r website

http://homemadecircuitsandschematics.blogspot.in/2011/12/super-simple-light-activated-switch.html

In that circuit when we adjust that preset ,i think it will switch on only after the dark will come to ldr


Give me one solution for to adjust time of switching on and off lights..................



PLEASE HELP ME........................................................................................

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March 7, 2013 at 1:10 PM delete

Sir,


My name is raigon jose and i am from kerala


And i made 1 solar street light with 12 VOLT 100 WATTS panel & 42 ah SMF battery & Lights 1 watt Edisson LED 20 Numbers

( 3 V x 4 ) A pair of 4 Led Series -------- 12 v ( 5 Rows) 20 WATTS Total

I have a problem faced from automatic ldr switching Circuit
LDR SWITCH CIRCUIT Installed in light Dom
LDR is installed inside the light cover
When evening 5 'O Clock the Light will be switch on & morning after 7.30 am will be switch off

When i searched about this problem i got u r website

http://homemadecircuitsandschematics.blogspot.in/2011/12/super-simple-light-activated-switch.html

In that circuit when we adjust that preset ,i think it will switch on only after the dark will come to ldr


Give me one solution for to adjust time of switching on and off lights..................



PLEASE HELP ME........................................................................................

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March 7, 2013 at 2:35 PM delete

Hello Raigon,

Make the first circuit given in this linl:

http://homemadecircuitsandschematics.blogspot.in/2012/03/how-to-use-ic-741-as-comparator.html

R1,R2,R3 = 10K, 1/4 watt

P1 = 100K pot.

Also connect a 10 K resistor across pin#6 and pin#3 of the IC.

And alos connect a 1K resistor across base/emitter of the transistor

transistor will be BC547

relay 12v/spdt

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Anonymous
May 19, 2013 at 6:04 PM delete

hi sir, This is naresh.
I want to save power. for that I need a switch works automatically. I have a problem with my cooler, having water pump separately. Now I want to set a switch to stop/start that pump automatically.

Aim is---> after working 10min, pump will switched OFF for 20min then again it will Switched ON for 10min and so on.............

how can I make this in my home.

please help me to my email address
g.naresh968@gmail.com

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May 20, 2013 at 11:13 AM delete

Hi Naresh,

make the following circuit:

http://homemadecircuitsandschematics.blogspot.in/2012/04/how-to-make-simple-programmable-timer.html

it needs just the following modification: the in4148 diode should be connected to pin3 and not pin15 as given in the diagram

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May 23, 2013 at 2:17 AM delete

Hi sir, i'm a new comer in this forum but i have been reading your articles based on electronics circuit and it's impressive, although I'm industrial electrical student and i tried hard to make electronic my hobby. Sir please i need your help,i made these circuit but it is not working and i used necessary components listed only that i used 500mA transformer but the same voltage rating. When i ON the switch the coil of relay energized and bulb light up,when i covered the ldr varied the resistor the bulb remain the same no change occurred, so sir i need some correction.

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May 23, 2013 at 9:37 AM delete

Hi Onwuzo,

I have removed the diode from the emitter of T1, do it in your circuit also, it will surely work now.

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May 24, 2013 at 11:15 AM delete

Hi swagatam, i removed the emmiter diode as you said but there was no effect the bulb still the same when i cover ldr. Please help sir tell me what i will do for the circuit to function well. Thanks

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May 24, 2013 at 9:41 PM delete

Hi Onwuzo,

the circuit should work now.

cover the LDR completely and adjust the preset so that the relay just activates. This will set up the circuit.

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May 27, 2013 at 3:31 AM delete

sir i have got it, it is now working thanks for your help and immediate responsed. Please sir can i get one with transformerless that can handle 500w fluorescent tube. Awaiting for your response

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May 27, 2013 at 10:13 AM delete

you can replace the transformer power supply network with the circuit shown in the following article:

http://homemadecircuitsandschematics.blogspot.in/2011/12/cheap-yet-useful-transformerless-power.html

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May 27, 2013 at 4:22 PM delete

sir how much maximum power can this particular circuit handle i mean bulb wattage.

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May 27, 2013 at 8:23 PM delete

it will depend on the relay contact ratings, you may upgrade it to any desired level.

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June 1, 2013 at 11:19 PM delete

CAN i use battery in this circuit ? How ?

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June 3, 2013 at 10:46 AM delete

HOW CAN I USE BATTERY IN THIS Circuit

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June 3, 2013 at 12:29 PM delete

this circuit is for AC application.

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June 15, 2013 at 3:53 PM delete

Hello sir, i had built the circuit and it worked fine only that am facing this problem now and want you to help me solve it. One day the circuit stopped working, when i troubleshoot i didn't saw any faults and later found out it was low voltage drop which fall 140v instead of 220v so when i knocked on the relay it make contact and light start illuminating. I have changed relay to 9v relay the same thing happened, and now we are having problem of low current always. so my question is there any way to do amendment so that it will function under circumstances of low voltage and normal voltage. Another question is that when dark start falling on the ldr relay start cracking noise which last about a minutes and 30seconds before it stopped and light will be steady vice versa. My question is there a way you should help me do this so that relay will pick one time when conducting instead of cracking noise please help.

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June 15, 2013 at 7:32 PM delete

replace the relay with a BT136 or similar triac.

do the following mods:

remove relay.
connect collector of T3 to positive directly.
connect emitter of T3 to ground via a 1K resistor.
connect triac extreme right lead to emitter via a 220 ohms resistor
connect extreme left lead of triac to ground
connect center lead to load and load to mains one point and mains other point to circuit ground.

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June 16, 2013 at 2:42 AM delete

sir am confusing in your descriptions u mention when i remove relay.
connect collector of T3 to positive
directly.
connect emitter of T3 to ground via a
1K resistor.
connect triac extreme right lead to emitter via a 220 ohms resistor
connect extreme left lead of triac to
ground
connect center lead to load and load
to mains one point and mains other
point to circuit ground. Sir am lost here first where is T3 in the circuit 2nd if i remove relay in place of bt136triac. I know the terminal pinout of triac bt136 which is terminal1, terminal2(tab), and gate3 so use it like this to describe to me.

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June 16, 2013 at 3:07 PM delete

Hi Onwuzo,

Please click the diagram to enlarge, T3 is the relay transistor...i know it should have been written as T2 but in the diagram it's indicated as T3.

center is termina2
gate is exterme right.

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Anonymous
July 10, 2013 at 11:57 AM delete

Hello ONWUZO, I built this circuit yesterday, I was happy it worked but as you have mentioned it makes a cracking noise for 1.5 minutes. That was your relay chattering due to the biasing voltage at the base of T1. My remedy is to add a 10k 1/4w resistor from the wiper of the pot VR1 to the base of T1. This will give C2 more time to hold the charge. If chatter persist add another 10uF/25V parallel to C2. It should work perfectly. Have fun experimenting!!!

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July 10, 2013 at 12:07 PM delete

...or simply connect a capacitor across the relay coil that will instantly stop all possibility of chattering.

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July 28, 2013 at 12:10 AM delete

Thanks sir for your explanation i appreciate your kindness. What value of cap do i add across relay coil.

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August 2, 2013 at 2:27 AM delete

Hi.
Actually i need your Contact number. Can you give your number? Or message me to this num. i'll call you. 9600582084

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August 2, 2013 at 9:04 PM delete

Hi,

Please feel free to contact me through my email ID

homemadecircuits@gmai.com

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Anonymous
October 5, 2013 at 1:33 PM delete

please tel me how to connect relay on a bread board...please help me out

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February 7, 2014 at 7:37 PM delete

Sir i want to make smart street light system..in this with the help of sensors the intensity of light inc. And decreases...plzz help

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February 9, 2014 at 11:29 AM delete

Harsimran you can try the following design:

http://homemadecircuitsandschematics.blogspot.in/2012/10/automatic-40-watt-led-solar-street.html

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April 14, 2014 at 5:20 PM delete

Sir,
what do you mean of (across relay coil)? does it mean (in parallel with the relay coil)?

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April 28, 2014 at 10:28 PM delete

Which pin of relay connect to supply and transitor?

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April 28, 2014 at 10:30 PM delete

Whow to connect realys pin to suppy and other components. Please explain in detail i have dast demo day after tomorrow.

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April 30, 2014 at 8:53 AM delete

The relay coil terminals will connect with those points

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June 14, 2014 at 11:06 AM delete

the center of the preset will go to T1 base, the other pins across R1 and ground.

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July 13, 2014 at 1:05 PM delete

I am trying to use BT136 and Transformerless-power supply like

http://homemadecircuitsandschematics.blogspot.in/2011/12/cheap-yet-useful-transformerless-power.html

But confused here " connect center lead to load and load to mains one point and mains other point to circuit ground."

What do you mean by "circuit ground" negative side of C2 ( if yes then how a 40 watt filament AC B22 base Indian Bulb could run) or Phase or Neutral of Mains of Transformer less power supply.

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July 13, 2014 at 7:16 PM delete

circuit ground is the line which is common to the triac right lead and the circuit negative. This line also gets connected with one of the mains inputs (preferably to neutral).

The other mains input (preferably phase) goes to the load wire as explained in your above comment.

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July 15, 2014 at 3:00 PM delete

220 ohm caught fire!!!

I have tried the following method to avoid Chattering of Relay at afternoon using BT136

""replace the relay with a BT136 or similar triac.

do the following mods:

remove relay.
connect collector of T3 to positive directly.
connect emitter of T3 to ground via a 1K resistor.
connect triac extreme right lead to emitter via a 220 ohms resistor
connect extreme left lead of triac to ground ( I have tired but not work then Connected to Phase)
connect center lead to load and load to mains one point and mains other point to circuit ground.( as well as Neutral)
circuit ground is the line which is common to the triac right lead and the circuit negative and the circuit negative (Left is already connected to negative as you told earlier) . This line also gets connected with one of the mains inputs (preferably to neutral).

Since Center pin of Triac is already connected to neural as well as negative, Left Pin of triac again if connect to negative or ground or neural circuit not completed so I connected Left pin of Triac to Phase and middle pin to neural or negative via load of a 40 watt bulb, I used a transformer less power-supply using 474k capacitor. But lamp lighten but within a second 220 ohm resistor caught fire I immediately turned off switch.

It will be great help if you post a diagram using BT136 and transformer less power-supply.

Thanks in advance

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July 16, 2014 at 11:39 AM delete

do not use bridge rectifier for the transformerless power supply, you can take the help of this article diagram:

http://homemadecircuitsandschematics.blogspot.in/2013/05/timeroscillator-circuit-for-exhaust-fans.html

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December 21, 2015 at 8:05 PM delete

Can the circuit be built without a control switch?

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March 3, 2016 at 10:19 PM delete

Beni
Sir! thankyou very much for your webesite.The AC is changed to DC.so which type of lamp may feet to it now to get enough light?

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March 4, 2016 at 11:14 AM delete

thanks Beni, the lamp can be seen connected with the AC mains via the relay contacts, so the lamp will be an AC lamp

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March 6, 2016 at 5:08 PM delete

sorry,i asked you before watching it good.thanks again

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