Dusk - Dawn Switch (LDR)

[ThomsCircuit]

I know there is a great deal of poor schematics available but I have been doing a good deal of research before i settled on this one to build from.

So I found a 12 year old article from EEWeb showcasing a D2D switch using a popular (They say) ORP12 LDR. I do not have that LDR. what I have is a KE10720 If you could help me determine if my LDR is a suitable replacement for the ORP12
The SR of the ORP is 515 to 730ns with a peak of 515. The KE10720 SR is 550 - 650ns with an unknown peak. >KE107 Datasheet<

I also do not have the UA741 or the BC109.
I do have the LM311 & the BC547. I'm pretty sure the NPN is a good substitution but unsure of the OpAmp

I will be using this to drive about 24 white LED's (FV 2.5 current 20ma) in series of 3 each from a 12 volt 1AMP transformer. The same transformer will be used to power the circuit. Could you please help me modify this circuit to work with my LDR and OpAmp?

Dusk to Dawn Switch

 

[audioguru]

An LM311 is not an opamp and it will not work in this circuit.
LDRs are in a cheap plastic case that gets sunburned then they need to be adjusted over and over. Today, cheap solar garden lights use a solar panel with a glass face. It lasts for many years.
A transformer produces AC, instead use a 12VDC AC to DC wall wart.

 

[augustinetez]

This one will work with the LM311.

I assume you want the LED's to come on when it is dark - you will need to swap the connections at pins 2 & 3 ie the junction of R1 & R2 go to pin 2 and the junction of R3 & R4 goes to pin 3.

The BC547 can be used to replace the BC107.

 

[ThomsCircuit]

LDRs are in a cheap plastic case that gets sunburned then they need to be adjusted over and over. Today, cheap solar garden lights use a solar panel with a glass face

Ok, thank you. So replace the LDR with a solar panel. Hmmm. Can you point out an example as im not charging anything.
Yes, the PS is a wall wart.

 

[ThomsCircuit]

I assume you want the LED's to come on when it is dark - you will need to swap the connections at pins 2 & 3 ie the junction of R1 & R2 go to pin 2 and the junction of R3 & R4 goes to pin 3.

Cool!
I understand these LDR's go bad from being exposed to sunlight (what doesn’t)
My setup will not be exposed to direct sun but just outdoors in daylight. Not in shade but in daylight just not direct sun. So in your opinion you think the LDR would react to these conditions?

 

[AnalogKid]

Yes. I've got two outside. One has been functioning since the 80's.

The sun up / low resistance might not be as low as in direct sunlight, but there should be plenty of resistance value change between indirect daylight and darkness.

ak

 

[augustinetez]

As AK says, it should be fine.

 

[ThomsCircuit]

Thank you AK and August.
I'm illuminating an analog clock with an LED placed at each hour segment. From front view the LEDs will be viewed from their sides so the majority of the light will be directed towards the center. Im using white but will add a fixed and adjustable pot so I can get just enough illumination.

 

[audioguru]

A dimming pot should have a series resistor to set the maximum brightness but the high current will fry an ordinary pot. The pot and resistor must feed a little power transistor emitter-follower that feeds the LEDs.

 

[ThomsCircuit]

A dimming pot should have a series resistor to set the maximum brightness but the high current will fry an ordinary pot. The pot and resistor must feed a little power transistor emitter-follower that feeds the LEDs.

Agreed. I thought about driving the LEDS from a transistor but was unsure how. This give me a good starting point.
Thank you

 

[ThomsCircuit]

Ive decided to use this design. I ordered the 741. The rest of the components I have.
The LM311 version had issues (according to the comments) from the site where it originated from.
This one is very well documented and included an explanation of and implementation for hysteresis. Something Ive been wanting to understand.
I added LED D2 so i can observe the circuit working and R2 in addition with the pot so the value does not go to 0.
Feedback about this design is welcome.
Thank you.

 

[Nigel Goodwin]

Ive decided to use this design. I ordered the 741. The rest of the components I have.
The LM311 version had issues (according to the comments) from the site where it originated from.
This one is very well documented and included an explanation of and implementation for hysteresis. Something Ive been wanting to understand.
I added LED D2 so i can observe the circuit working and R2 in addition with the pot so the value does not go to 0.
Feedback about this design is welcome.
Thank you.
View attachment 137777

Why would you order an antique low spec opamp, when any opamp would do? - an LM311 isn't an opamp, but the 'standard' devices are things like the TL07x, TL08x etc.

 

[rjenkinsgb]

An LM311 is not an opamp and it will not work in this circuit.

Why??
The 741 is just being used as a comparator with extra hysteresis via the 270K resistor.

Just arrange the 311 output with collector to power and emitter to the transistor drive resistors.
(Or for the circuit in post #11, keep emitter to 0V and collector out).

The extra hysteresis is a good thing for a dusk to dawn switch to prevent repeated changes when light levels are near the threshold - or oscillation if some light from the source it's controlling can get back to the sensor.

 

[ThomsCircuit]

Why would you order an antique low spec opamp, when any opamp would do? - an LM311 isn't an opamp, but the 'standard' devices are things like the TL07x, TL08x etc.

The short answer is that I'm not experienced to know the difference. I'm glad you told me that they can be interchanged without affecting the circuit.

 

[ThomsCircuit]

The 741 is just being used as a comparator with extra hysteresis via the 270K resistor.

Just arrange the 311 output with collector to power and emitter to the transistor drive resistors.
(Or for the circuit in post #11, keep emitter to 0V and collector out).

Thank you rj. I chose the layout in post #11 over that in #1 because it was documented so much better. I am interested in subbing the 741 for the 311. I'm not clear on how to connect it but I'll update the schematic and we can go from there.

 

[ThomsCircuit]

One thing i noticed is the transistor in #11 is a PNP. I mis-labeled its equivalent. I will be using 2N3906

 

[ThomsCircuit]

OK here is my attempt to replace 741 with LM311. Did I get it correct?

 

[Nigel Goodwin]

For hysteresis the feedback needs to go to the +ve input.

 

[ThomsCircuit]

For hysteresis the feedback needs to go to the +ve input.

Should i also short 5+6 together

 

[ThomsCircuit]

I am assuming that ve+ is pin4
I have looked for clarification (google) but found nothing definitive