LED on after dark with LDR

[gary350]

I am trying to combine these 2 circuits so the LED flasher on the right will be ON after dark and OFF during the day, do I have them connected the correct way?

I am using the 45 year old LDR I already have. Once I get a circuit that work I will order new LDRs to change my 18 LED flashers so they only come ON after dark to save the batteries. This should almost double the life of the battery. AA batteries only lasted 1 month. D batteries have been doing good for 2 months.

 

[rjenkinsgb]

You could just connect the whole second circuit in place of the LED and resistor in the first one.
Note that if the LDR light resistance is correct (66 ohms) you are putting far more current than required through the base of the transistor, something over 30mA which is a big, pointless, drain on the battery... Add another resistor in series to limit that.


Or, you could use a rather different circuit that has both functions already, as used in road warning lights:

https://www.rlocman.ru/shem/i/members.shaw.ca/novotill-FlashingRoadBarricade-circuit1.png

The one I saw in bits used an LDR rather than a phototransistor, just try it with your LDR where the transistor is shown.
Use your LED and resistor in place of the filament lamp.

It should work on 3V, though it may need an extra resistor across the LED (eg. 10K) so the cap is pulled to 0V between flashes.

I believe the original version I saw was a delayed schmitt trigger circuit, with an R-C time constant included; if it was dark, the light switched on after a delay, if it was light (sunlight or the lamp itself), it switched off after a delay - thought it is over 40 years since I messed with that, so I could be wrong.

 

[gary350]

I decided to us a variable resistor not a fixed resistor, I have 18 LED flashers about 6 are in the sun the other 12 are in large and smaller trees or north side of house or shed with different amounts of shade so the adjustable resistor will let me adjust each one according to how much shade there is. New LDRs may be different than my 40 year old LDR adjustable resistor might be helpful for that too. Tomorrow I will check see what I have to work with I hope to have some 1K or 5K variable resistors but I don't think I have anything less than 10K for R5. As the sun passes over every day the amount of sun each of the 18 LED flashers gets will change easy adjustment will be easier.

 

[audioguru]

My solar garden lights use a solar panel to charge one AAA Ni-MH battery cell and have a charger circuit and a voltage boosting circuit. They do not use an old LDR, instead their IC uses the solar panel to see light and dark. Some of them cost $1.00 at Walmart but I replaced the cheapo Chinese battery cell with a good one. I also replace the original white LED with a colors changing LED. They charge all day and are bright all night for years.

 

[gary350]

My solar garden lights use a solar panel to charge one AAA Ni-MH battery cell and have a charger circuit and a voltage boosting circuit. They do not use an old LDR, instead their IC uses the solar panel to see light and dark. Some of them cost $1.00 at Walmart but I replaced the cheapo Chinese battery cell with a good one. I also replace the original white LED with a colors changing LED. They charge all day and are bright all night for years.

I have several solar panel lights that I salvaged because water rusted the battery contacts away now there are not contacts for the 2 AA batteries but I saved the circuit boards and solar sells. Problem I have they will not charge the batteries while hanging in a shade tree. No direct sun light no charge. If i put 15 ft of wire on the solar cell I can get it out to the tip end of a tree limb then it works for a few days until leaves grow larger and cover up the photo cells. 2 weeks ago is the first time we have seen the Tennessee sky since November our winters are dark over cast sky solar lights do nothing for 6 months all winter. Even in summer we have cloudy sky about 50% clouds then solar will work. My solar patio lights are working again but I have noticed they only get enough sun to stay charged for 2 hours after dark.

 

[audioguru]

The bottom of a cheap solar panel must not get wet. Cheap solar panels have a plastic top that gets sunburned and turns cloudy. Cheap but good quality solar panels have a glass top that lasts for years.

 

[gary350]

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