Ok i'm off on another project. i'm a newbie so take it easy on my. I'm looking for a circuit to take a photocell and have it turn on an led using 2 aaa 1.5volt batteries and trun on the LED around Dark. can anyone point me in the right direction?

 

You know those solar garden lights your neighbor has down the street... Just kidding, you are looking for a dark-activated switch. Several circuits in this forum already (posted three different ones myself...). You didn't mention what kind of LED you plan on using. If it's white, 2 rechargables won't work, disposiables won't last very long, you'll need a boost converter. Red or amber will work okay. If you're in a hurry, search the forum or the web, plenty of circuits. I'll search the hard drive, and post the on I've been using a little later (already in the past posts some place...).

 

actually looking at a blinking LED

 

here is the link to the LED i have:http://www.radioshack.com/product/in...entPage=search

 

i know it runs great hooked direct to 2 1.5v AA or AAA bats

 

Give these a try!

My only concern is if the 3V is enough, and if so for how long.

Attached Images

laLED1.jpg (38.5 KB, 31 views)

 

either way i hook this up i get the same results. when dark it shuts off

 

i got it working. stupid me. no my question is.... how do i fine tune it? i don't want the LED to come on untill it is almost night fall.

 

Team_NightStalker wrote: "how do i fine tune it? i don't want the LED to come on until it is almost night fall."

The 50k pot allows for some light sensitivity adjustment, but that really is a problem with many of the store-bought side-walk lights and this circuit as well.

I ended up using a rechargeable batt. with a 741 op-amp and a Photo-transistor instead. I ended up with a very sensitive circuit.

The following circuit is what I had come up with:
Note: The 10k pot is needed for the sensitivity adjust.

Maybe some of the real guru's can simplify this circuit.

Attached Images

Ultra Sensitive Light switch.jpg (75.6 KB, 23 views)

 

That's fine but it won't run from a 3V battery.

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How about this!
The TLC25L2 can operate on a single supply voltage as low as 1.4v.

Attached Images

Ultra Sensitive Light switch3.jpg (23.3 KB, 19 views)

 

i added a resistor on the one side of the photocell to the other ground and it helped some but not alot. the lower the resistor should make it turn on when darker correct? i used a 470. what else could be used to turn the LED on when darker out?

 

TEAM_NightStalker,

The first circuit I posted had R2 as a 50k pot, this should be the main control for sensitivity. Changing R3 to a 470 ohm resistor may help, but minimally. I've played with resistor values and did not get the desired results with this circuit.

The 2nd circuit post, maybe the the 3rd circuit post are far superior to the first in controlling when the LED turns on.

 

But the circuit still won't work!

R4 and R5 form a potential divider so when U1 goes high the base voltage will only be 0.5V so the transistor will never turn on!

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I also post at the following sites:
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Screen name: Aloone_Jonez
And http://www.silicontronics.com, same screen name as here.

 

RadioCrap war-surplus junk never has any spec's.
Operating voltage?
Operating current?
They don't know so you also don't know until tou smoke it.

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