how this cricuit will work!!

[rohaan]

hey ..
there is the circiuit diagram of Light/dark detctor..
please tell me how it will work..?

i mean when there is dark..so what will be the respone??
the realy wont wokr..thats it..!
i dun have to put any led or some thing to show it clearly..???
please senior members help me out

 

[ericgibbs]

hey ..
there is the circiuit diagram of Light/dark detctor..
please tell me how it will work..?

i mean when there is dark..so what will be the respone??
the realy wont wokr..thats it..!
i dun have to put any led or some thing to show it clearly..???
please senior members help me out

Hi,
The circuit is a poor design, where did get the design from.?

I think it supposed to energise the relay when the light detector is dark.?

 

[rohaan]

relay work when dark or when there is light..?
please make me sure bout it???

 

[ericgibbs]

relay work when dark or when there is light..?
please make me sure bout it???

hi,
When Q2 is dark it has a higher resistance compared to when its lit.

So as Q2 gets darker the the voltage on Q2 collector will rise, this will increase the base votage of Q1. This increase of base voltage will make Q1 conduct more current thru the relay.

Eventually this increase in Q1 current will enegise the relay.

When Q2 gets more light its resistance falls, which reduces the Q2 collector voltage and so Q1 base voltage falls which causes a reduction in Q1 current and so eventually the current falls low enough that the relay de-energises.

The pot in the collector of Q2 is 'supposed' to enable the setting of the point of light/dark, when the relay operates.

The circuit is a poor design, where did get the design from.?

Does this help.?

 

[rohaan]

well thanks for explainging...!
but may i ask that what do u mean by poor design?
is it mean that if i implement it so it wont work or what??
please make me clear this thing cus i m supposed to start work on it by tomorrow..
thanks again for ur explanation

 

[Torben]

well thanks for explainging...!
but may i ask that what do u mean by poor design?
is it mean that if i implement it so it wont work or what??
please make me clear this thing cus i m supposed to start work on it by tomorrow..
thanks again for ur explanation

Isn't the point of schoolwork that *you* are supposed to do it?


Torben

 

[rohaan]

well,its kinda of a University work..
which i have to submitt on the date..
Gibbs
could u please tell me whats the meaning Poor DEsign ??

Rohaan

 

[ericgibbs]

well,its kinda of a University work..
which i have to submitt on the date..
Gibbs
could u please tell me whats the meaning Poor DEsign ??

Rohaan

hi,
Is it your design.?:confused:

The pot is wired/connected in such a way that it will be difficult, if not impossible to set up the light/dark point.

You have not stated the working voltage of the relay coil.

You will never get the full 9V at the emitter of Q1.

If you have built this already, measure some voltages light and dark and post them on the forum..

 

[rohaan]

First thing, i Didnt make this Circuit i jus got it from the net..
and the other thing i didnt start working yet..
ill do it tomorrow..
u mean this Circuit will give hard time?
how to connect Pot.
listen if i set the pot when the relay is energised and the light is on the photo.TRan,
so will the relay stop when there is no light on the phot.Tran..?
or do tell me how to set this Pot..:s
well the pot is connected as 1 leg to the 9v and the other one is connected to the Q2 collector and Q1 base..
m i right???

 

[BaCaRdi]

Am I crazy or should there be a protection diode for the inductive load?

-BaC

 

[ericgibbs]

First thing, i Didnt make this Circuit i jus got it from the net..
and the other thing i didnt start working yet..
ill do it tomorrow..
u mean this Circuit will give hard time?
how to connect Pot.
listen if i set the pot when the relay is energised and the light is on the photo.TRan,
so will the relay stop when there is no light on the phot.Tran..?
or do tell me how to set this Pot..:s
well the pot is connected as 1 leg to the 9v and the other one is connected to the Q2 collector and Q1 base..
m i right???

hi rohaan,

What is the relay coil voltage and operating current.?

Whats the specification of the photodector Q1.?

What is transistor Q1.

Can you post the web link, so that we can read what the author claims.?

 

[rohaan]

ya there is a protection diode ..
but in this picture it is not mentioned..!

 

[ericgibbs]

Am I crazy or should there be a protection diode for the inductive load?

-BaC

Hi,
I cant say if you are crazy or not, I dont know you well enough..

But you are correct, a diode would be advisable.

 

[Nigel Goodwin]

well,its kinda of a University work..
which i have to submitt on the date..

If it's for University work then I wouldn't expect to get any sort of decent mark at all for handing something like that in - as suggested, it's an incredibly poor circuit, probably 'designed' by a 9 or 10 year old?.

Presumably you're not doing an Electronics degree?, as you wouldn't get on the course if you need to ask such basic questions.

 

[rohaan]

No its not mentioned the relay coil Voltage..is it necessary?
the photo transistor is the Q2 not Q1.where Q1 is simple npn 3904.
please make me clear bout pot..
how to set it?

 

[rohaan]

well
Gibbs, this is the link
https://www.electronics-lab.com/projects/sensors/022/index.html

 

[rohaan]

ya
Nigel
i jus wanted to know this thing that is it acccpetable by the teachers whom i have to submit..
because i didnt work on this type of project..
so i jus search on the net & found it..
i have to work nething BJT with sensing..
well thanks for ur comment !!

 

[BaCaRdi]

I forgot my mind reading hat home lol

-BaC

ya there is a protection diode ..
but in this picture it is not mentioned..!

 

[ericgibbs]

hi rohaan.

Look a this link, the first project is a light/dark relay..

https://www.hobbyprojects.com/L/Light_Detectors.html


EDIT:
Two more links, the Omron link is useful.

**broken link removed**

https://www.electro-tech-online.com/custompdfs/2008/04/en-ph_micro_info.pdf

 

[Nigel Goodwin]

well
Gibbs, this is the link
https://www.electronics-lab.com/projects/sensors/022/index.html

Electronics-labs is well known for being full of badly designed projects that don't work - this one is particularly poor.