# Light sensor circuit..... sensitivity adjustment using resistors

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#### hoghunter

##### Member
I have designed this simple dark sensor circuit that will turn on some LEDs at nightfall. After testing, it seems to be too sensitive, meaning it takes a fair amount of light to turn the circuit OFF. This would allow the lights to illuminate well before sunset and to keep working further into the morning. Even sitting on my kitchen table with a light on above, it does does not turn the led off. I have to add a brighter light. And then, just a shadow from my hand will turn it on.
My question is, how can I adjust the sensitivity to require much less light to turn the circuit off? I'm assuming an adjustment to my resistor combination would do it, but not sure..... thanks.
P.S. the system is 12v DC

#### ronsimpson

##### Well-Known Member
The LM358 will work then the inputs are in between "GND" and "POS"-1.5V. (will not work if too close to "POS")

You could replace R4 & R5 with a POT. Then you can set the voltage to a different level. (with in limits see above)
OR
I don't know which LDR you are using. Try changing R3 to 100k or 1k. I don't know which.
R4&R5 sets a voltage to 1/2POS.
R3&LDR sets a voltage.
The LM358 compares these two voltages.
So you need to change something in this balancing act.

#### hoghunter

##### Member
The LM358 will work then the inputs are in between "GND" and "POS"-1.5V. (will not work if too close to "POS")

You could replace R4 & R5 with a POT. Then you can set the voltage to a different level. (with in limits see above)
OR
I don't know which LDR you are using. Try changing R3 to 100k or 1k. I don't know which.
R4&R5 sets a voltage to 1/2POS.
R3&LDR sets a voltage.
The LM358 compares these two voltages.
So you need to change something in this balancing act.
Thanks Ron,
I'll test some different R values and see what works best.

#### hoghunter

##### Member
I think 47k works well for now. I appreciate the help.

#### ronsimpson

##### Well-Known Member
I appreciate the help.
Hit the "like" button. I do not know why but I am trying to hit 1000. thanks

#### AnalogKid

##### Well-Known Member
Interesting way to draw a schematic. Are you in Australia?

ak

#### hoghunter

##### Member
Interesting way to draw a schematic. Are you in Australia?

ak
Haha.... Texas actually.. I'm new at all of this. I guess the pos+ would usually be on top??

#### hoghunter

##### Member
Now I'm depressed...... nobody 'likes' me

#### Inquisitive

##### Super Moderator
Hit the "like" button. I do not know why but I am trying to hit 1000. thanks
Thought I'd add my 1 click(s) worth.

##### Well-Known Member
Now I'm depressed...... nobody 'likes' me
I like the name. Anyone in Texas going by Hog Hunter can't be all that disliked.

I also gave Ron Simpson a "like" because I like his name (and his post was good).

Ron

#### hoghunter

##### Member
Thanks guys, I'm a happy camper now!!

Reloadron, I'm in Texas now, but was born in Cleveland.... Euclid area

##### Well-Known Member
Thanks guys, I'm a happy camper now!!

Reloadron, I'm in Texas now, but was born in Cleveland.... Euclid area
I was NYC born and raised and wish like hell I was in Texas.

Ron

#### AnalogKid

##### Well-Known Member
Born a Buckeye, still a Buckeye.

ak

#### hoghunter

##### Member
I do like the Buckeye state, but nothing beats Texas Been here since '72

#### hoghunter

##### Member
I do have another electronics question for you guys..... the product I'm putting together requires a 5v step down regulator to power the digispark controller. I am currently using modules to step down the voltage. Can you recommend a simple circuit that I could add to my pcb that would step down 12v to 5v & 24v to 5v?

#### ronsimpson

##### Well-Known Member
step down 12v to 5v & 24v to 5v?
How much current?
Is heat a problem? (linear regulator like a LM7805 can get hot)

#### AnalogKid

##### Well-Known Member
Little buck regulator modules on ebay are disgustingly cheap, and turning them into a "component" to install on a larger pc board is not difficult. You would have to be building a lot of assemblies to make your own design cost effective.

ak

#### hoghunter

##### Member
Great points. I think I'll stick with the small boards I'm using now. I'll be able to plug them onto the new main board.
thanks y'all

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