URGENT. Can this project work?? Pls help me to modify.

[themaestro]

Hello there,
This purpose of this circuit is to switch on the bulb during nighttime and switch off the bulb during daytime. But so far i tested it on the bread board and it couldnt work. I dont know whether it's my personal problem or the schematic problem, can anyone help me on this?? plus, I would like to add a timer of 5hours to the circuit. The main purpose of the timer is to automatically switch off the circuit after 5hours ( assuming that the person sleeps 5hours after it's dark.) and repeats the cycle daily. A friend of mine suggested that i should put a timer in between the Zener Diode and the BC547 Transistor. But i'm unsure of the value. Just now when i was experimenting, the whole building short-circuited thrice. HELP PLS.... if possible pls attach a schematic as well.. thanks. my dateline is tomorrow =(

**broken link removed**[/IMG]

 

[MikeMl]

Hard to do without a schematic?

 

[ericgibbs]

hi,
There is no circuit diagram on the PM you sent me.??

 

[themaestro]

Sorry about that. Here it is.

 

[ericgibbs]

Sorry about that. Here it is.

Disconnect your LDR from the circuit and measure with ohm meter the resistance of the LDR when it dark and light, let us know what you measure.?

EDIT:
Its works OK in simulation

 

[themaestro]

Disconnect your LDR from the circuit and measure with ohm meter the resistance of the LDR when it dark and light, let us know what you measure.?

Just now i measured before. if i'm not mistaken, when bright, it's 100+k ohms. when it's dark it's 400k ohms

 

[ericgibbs]

Just now i measured before. if i'm not mistaken, when bright, it's 100+k ohms. when it's dark it's 400k ohms

hi,
With that LDR the circuit will not work.
Change the values of the two resistors R1 and R2 to these values and it should work.

 

[themaestro]

hi,
With that LDR the circuit will not work.
Change the values of the two resistors R1 and R2 to these values and it should work.

oh i see! Thank you very much for the info! By the way in the simulation, the value of the dc is 15V, where as the original one is 12v. Will it work the same by changing the R1 to 470k, and R2 to 50k?
Let's say that i was wrong about the values during bright and dark, how can i vary the values of R1,R2 when i measure the ldr values tomorrow? Should the value of R1 be higher than the resistance(dark) and R2 lower than resistance(light). Sorry for being so ignorant and shallow about the circuit.

 

[ericgibbs]

oh i see! Thank you very much for the info! By the way in the simulation, the value of the dc is 15V, where as the original one is 12v. Will it work the same by changing the R1 to 470k, and R2 to 50k?
Let's say that i was wrong about the values during bright and dark, how can i vary the values of R1,R2 when i measure the ldr values tomorrow? Should the value of R1 be higher than the resistance(dark) and R2 lower than resistance(light). Sorry for being so ignorant and shallow about the circuit.

hi,
The 12v is output of the transformer, which when rectified and smoothed will about +15V, so that will not affect the circuit.
Re-measure the LDR, light and dark, post what you measure.

 

[jayasri.N]

please send a schematic representation

 

[themaestro]

please send a schematic representation

here it is.

 

[themaestro]

hi,
The 12v is output of the transformer, which when rectified and smoothed will about +15V, so that will not affect the circuit.
Re-measure the LDR, light and dark, post what you measure.

I see. thanks for the explanation. I've measured the resistance. It's around 600k during dark. and it varies between 80~200k during light. I tested out the circuit just now but it still didnt work. When i switch on the ac from the right hand side(linked to the bulb and relay, you can see it from the schematic), and i turn on the left hand side ac, the bulb lights up no matter what happens to the brightness of the room. I dont know what went wrong. When i switch off the ac for the left hand side, i can hear the relay *click* once and switch.

 

[colin55]

The relay is activated when light ceases to fall on the LDR. The resistance of the LDR increases and the BC557 transistor turns off. This allows the voltage on the common terminal of the 7806 to rise and the output voltage rises.
When the voltage rises above 9v, the base of the BC547 sees a turn-on voltage and the relay is energised.
The original circuit is a very complex for such as simple task.
A much simpler circuit is shown below:
**broken link removed**

 

[themaestro]

The relay is activated when light ceases to fall on the LDR. The resistance of the LDR increases and the BC557 transistor turns off. This allows the voltage on the common terminal of the 7806 to rise and the output voltage rises.
When the voltage rises above 9v, the base of the BC547 sees a turn-on voltage and the relay is energised.
The original circuit is a very complex for such as simple task.
A much simpler circuit is shown below:
**broken link removed**

Thanks for your reply. I have already done the PCB for the schematic that i've previously posted and i have to carry on with it because my dateline is 2 days from now, plus i have to write a 50 page report. Can you tell me what could have went wrong with my circuit? I checked all the parts n they were fine. But for the diode(D5) in my schematic when i solder it to the PCB, it is shorted. I used the multimeter to check the ends of the diode and there was a "beep" sound. The bulb would light up no matter what happened but now it couldnt light up at all. I think 1 of the parts might have been spoilt. Help me please. It's very important to me. By the way, i changed the white LED to a yellow one. the VR1=50k ohm. R2=470k ohm.