[SOLVED] Help me to create a Light Sensitive (with LDR) Circuit

[bibintm]

Hi Friends,
Can anyone give me a diagram for the following circuit?

:arrow:A mini motor (1.5v or 3v) must work when light falls on an LDR.

>It would be better if it works on lowest power to say 3v
>circuit shouldnt use a relay
>motor must start when light falls on LDR
>No problem if motor doesnt stop when light is off

:smile:Waiting for your replies.
Thanks in advance
bibintm@ymail.com

 

[milind.a.kulkarni]

You can try this circuit ....but making it work on 1.5 v will not be possible you need at least 3v or above and you need to tune 1K pot according to your need....

Good Luck

 

[bibintm]

Thanks to reply brother, I'll try it today.
Thanks, thanks thanks...

 

[bibintm]

Not working!
found light has no effect on motor.
When I short LDR legs, motor is working.

Will there be any problem with transistor ( written ' COIL CL100S ' on it) I bought? Or any problem with LDR?
Plz reply

 

[Pjdd]

milind's circuit is OK in principle but there may be some practical shortcomings. If you can measure the resistance of the LDR, it will help in designing a more efficient circuit. If you have a multimeter, remove the LDR from the circuit and measure its resistance, first when it's dark and then when there's light falling on it. The amount of light should be about the same level at which you want the motor to turn on.

You already know that the resistance of an LDR changes when light falls on it. But the resistance range differs widely for different LDRs, which is why it's important to know the approximate resistance range of the unit you have.

By the way, it's not a good idea to short the LDR legs when it's in circuit and power is on. It won't harm the LDR but it will definitely harm the transistor if you keep doing it.

 

[milind.a.kulkarni]

Good Point Pjdd.....actually.....I forgot to mention that point one has to measure the LDR resistance from multi-meter....when light fall on LDR there and when light is not following on LDR.....Based on the those values one need to select the the value of variable resistor such that transistor biasing is proper....bibintm you can try to change the variable resistors values to 10K and 100K and try this....or post the input voltage that you are giving and range of the resistance for LDR on the forum...we can try to make the circuit working .....Also I like Pjdd point of shorting the LDR .....as he said .....it is not a good idea of shorting the LDR when circuit is powered on......Second thing which I will like to share is if you specification of LDR then try to have LDR with more current rating ....may also help ....

Good Luck

 

[bibintm]

ok, i bought 10k and 100k variable resistors today. Will reply after trying.

Thank u all.

 

[bibintm]

Sorry to say, but it is not working on 1k, 10k, 100k resistors. Motor works when adjusting resistors, but LDR has no effect on it.
LDR shows 15-16 k resistance on light.
Will you help me or I should give up?

 

[bibintm]

Where're you guys?

I tried the circuit at lower volts and found it is sensitive by adjusting resistor (not enough to switch on and switch off motor, I just can adjust speed).
another thing us that motor works faster on dark and slower on light. Confused! I'm getting opposite result.

 

[milind.a.kulkarni]

hi bibintm....sorry for late responce.....when you have LDR resistance is 15K or 16K on light following what is a value of LDR when there is no light i mean when it is dark....it must be 100k or more.....the behavour that you are getting is oppsite responce....i am also superised.....i think with 10K pot you should get the responce like in dark motor should be not running and on falling of light on LDR motor should start running......

refer-

**broken link removed**

good luck

 

[Pjdd]

Sorry to say, but it is not working on 1k, 10k, 100k resistors. Motor works when adjusting resistors, but LDR has no effect on it.
LDR shows 15-16 k resistance on light.
Will you help me or I should give up?

Please pay attention to what information others ask you to provide. I asked you to measure the LDR resistance in the dark and when there's light falling on it. In the dark means when you expect it to be off. It is very difficult to design a reliable circuit without proper information.

Where're you guys?

I tried the circuit at lower volts and found it is sensitive by adjusting resistor (not enough to switch on and switch off motor, I just can adjust speed).
another thing us that motor works faster on dark and slower on light. Confused! I'm getting opposite result.

Are you sure you know which pin is which on the transistor?

---------- Post added at 22:38 ---------- Previous post was at 21:39 ----------

The circuit below should work. It's still not perfect. If it still turns on in the dark, substitute the 10k resistor with an adjustable one.

If you want a better circuit with a reliable snap on-off action and if you can work with opamps, I can design one for you using an opamp.

 

[bibintm]

Resistance of LDR in dark is infinite (shows no continuity) and in light is 16k.
The motor works on 1.5v also. Sorry, I just found it.

@pjdd
I'll try the new circuit after buying components tomorrow.

Thanks for keep helping me, happy new year.

 

[mrarslanahmed]

i dont think it is necessary to check resisitance of LDR .We are using potentiometer why not to turn its knob to set the threshold.

---------- Post added at 00:20 ---------- Previous post was at 00:15 ----------

If you want a better circuit with a reliable snap on-off action and if you can work with opamps, I can design one for you using an opamp.

i have one question that is can opamp provide that much current to drive motor please do tell me because i am having problem of limited current from omamp.

 

[Pjdd]

Checking the resistance of the LDR is not absolutely essential, but it's very desireable because different LDR models differ very widely in their properties. I'm saying this from my own experiences of designing and building professional products using LDRs in the past. For example, under the same light condition, one type may have a resistance of a few k-ohms while another may be of tens of k-ohms. To make a successful design without lots of trial and error, we have to be able to estimate the approximate resistance range.