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electronic candle using ldr and thermistor

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anny999

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i have attached image and description of my circuit. please go through it, if you can, to understand the details.
i made this circuit on breadboard and sometimes the bulb glows and sometimes doesn't but only till ldr is shown light :(
it should remain on till i blow air near thermistor.
i am also attaching image of my breadboard circuit.....please help
 

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A fan is not an air conditioner.
If you blow air on a thermistor that is already at the same temperature as the air then its temperature does not change and the thermistor does nothing.
But if you use a fan to blow air on you then you will feel the coolness because your body is alive (warm) and is not dead (cool).
 
anny999 said:
i have attached image and description of my circuit. please go through it, if you can, to understand the details.
i made this circuit on breadboard and sometimes the bulb glows and sometimes doesn't but only till ldr is shown light :(
it should remain on till i blow air near thermistor.
i am also attaching image of my breadboard circuit.....please help
Click to expand...

Turn On the circuit give two minute time ensure thermister is not exposed to air now bring the light near LDR now most probably light will glow up, some times may not. Now vary the 10k pot in the opamp input so that it will remain in ON position when no light is applied.

Actually the LDR mechanism is easier than turn off mechanism, The thermister may not work if you turn off after lof time because its temperature will be more. If there is a cap in the thermister input it would be better but i am not sure about the thermister heat change timings.

- - - Updated - - -

If you have any problem doing this give 0 in the place of 555 IC 6 th pin and try lighting.

If that works fine then check the opamp output to be low on ordinary time and high on the time of cooling..
 

sorry i am attaching my circiut diagram and description now...

 

sorry i am late, but i wanted to share this. i accidently removed the variable resistor and put nothing in place of it. and guess what, the bulb glows and remains on even after removing light source near it!
though i am still having trouble with thermistor part. i even tried to cool it down using an ice cube wrapped in aluminium foil, but still it doesn't blow the led out.
Venkadesh_M said:
If you have any problem doing this give 0 in the place of 555 IC 6 th pin and try lighting.

If that works fine then check the opamp output to be low on ordinary time and high on the time of cooling..
Click to expand...

i tried this but when i give 0 i.e. ground to pin 6 led simply blows out. what should i do??
 

Venkadesh_M said:
Turn On the circuit give two minute time ensure thermister is not exposed to air now bring the light near LDR now most probably light will glow up, some times may not. Now vary the 10k pot in the opamp input so that it will remain in ON position when no light is applied.

Actually the LDR mechanism is easier than turn off mechanism, The thermister may not work if you turn off after lof time because its temperature will be more. If there is a cap in the thermister input it would be better but i am not sure about the thermister heat change timings.

- - - Updated - - -

If you have any problem doing this give 0 in the place of 555 IC 6 th pin and try lighting.

If that works fine then check the opamp output to be low on ordinary time and high on the time of cooling..
Click to expand...

i accidently removed 10k ohm variable resistor and now the bulb glows even if matchstick blows out! but thermistor part is still not working. i even tried cooling it with ice.
also i gave ground to pin 6 as per @venkadesh_M but on doing this bulb simply blows off(not because of thermistor)
what should i do?
 

anny999 said:
i accidently removed 10k ohm variable resistor and now the bulb glows even if matchstick blows out! but thermistor part is still not working. i even tried cooling it with ice.
also i gave ground to pin 6 as per @venkadesh_M but on doing this bulb simply blows off(not because of thermistor)
what should i do?
Click to expand...

Have you checked the value of the thermistor. When its in the room temperature? And try checking the value when you blow air onto it. See if there is significant change in the resistance value.
 

Venkadesh_M said:
Its a pretty simple circuit dont worry.. What do you mean blow? did you mean glow?
Click to expand...

yeah it is simple :) and by bulb blowing off i mean that bulb turns off

- - - Updated - - -

Suhas Anand said:
No. You are trying to switch off the light when you blow air onto the thermistor right?
Click to expand...

yes, i am trying to switch off the light by blowing air onto the thermistor but i dont think that one cool the temperature of thermistor by blowing air to it...is it possible?



Suhas Anand said:
Have you checked the value of the thermistor. When its in the room temperature? And try checking the value when you blow air onto it. See if there is significant change in the resistance value.
Click to expand...

how can i check the value of thermistor? and what value? are you talking about resistance?

and i the thermistor i have used is of 10 ohms value. it worked on breadboard. waht happened was the bulb glowed on showing light to ldr, kept on glowing, then after a minute i touched thermistor and bulb turned off. this happened quite a lot of times. so my circuit was working...kind of

but now it is not working. i have no idea why :(
 

Yeah. Check the value of the thermistor using multimeter. And in the circuit they have mentioned a 150 ohm thermistor. Y r u using 10 ohms?
If u are using a different valued thermistor u have to use a different resistor(corresponding to the resistance of thermistor) in the voltage divider for proper functioning of the circuit.
 
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