Need help !! LDR night light

Mr.K · Dec 15, 2016

Hello there.

I found a circuit guide to make a LDR night light. I have got a question :

the 10K resistor reduces the brightness of LED quite remarkable. I tested with lower resistors , even less than 1K resistors. Brightness increases as resistor lowers , but the problem is that it also reduces sensitivity of LDR. I mean If I use a 1K resistor , for instance , then the LDR needs too much brightness of light to turn the LED off.
What to do ?

Thanks

* I don't use a resistor between LED and power source (in the picture which is marked as "If needed")

* I use 7-millimeter LDR . All other specifications are similar to the photo of circuit I attached

Audioguru · Dec 15, 2016

Select a more sensitive LDR, they are all different. Mine have sensitivities of 10 to 1.
Select a transistor with a higher hFE at high currents like a 2N4401 or a darlington transistor then the base resistor value can be higher.
Use a resistor in series with the LEDs to prevent them from burning out.

AnalogKid · Dec 15, 2016

You will get more even illumination and longer LED life if you have one current limiting resistor for *each* LED. Also, you are not going to get very "snappy" response from a single transistor circuit with no hysteresis. Consider two transistors, with at least one of them being a 2N7000 or 7002.

ak

KTW · Dec 15, 2016

I built a night light using an LDR enabled PIR sensor so it only operates when activated.
It has to be quite dark to work.

Mr.K · Dec 16, 2016

Thanks guys

Need help !! LDR night light

Mr.K

Audioguru

AnalogKid

KTW

Mr.K

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