Need help with a photocell.


Joined Dec 5, 2009
Hi Mike, This is a modified garden solar light mounted on my caravan, the LED is glued where the finger is & shines down the side of the van door. There is plenty of light on dark nights to see the keys & key hole. Been there for a couple of years now. Daryl
debe, is that the stock LED?


Joined Sep 21, 2010
Still has orig battery in it. Just decided to try & draw the circuit in one, The solar panel in it turns the LED off during the day when its charging, obviously the transistor is boosting the 1.2V for the LED as its quite bright.



Joined Dec 20, 2007
The solar panel of a cheap solar garden light must be in direct sunlight all day long for its battery cell to light the LED dimmly for an hour at night in winter. The LED does not light following a cloudy day.


Joined Sep 9, 2010
I suppose I should have been a bit clearer with my description. I want to make a light that is fairly intense to light up the key hole in my exterior door.
A single, cheap LED at half it's rated current capacity will be plenty of light for this use.
Sure, I could just leave the porch light on but...bear with me, I don't want to do that. A garden light won't cut it. Plus there may not be enough light to recharge the cell(s).
My suggestion wasn't to use the solar panel for battery charging, just the internal electronics. These will give you the CdS photocell for on/off control and as a bonus you'll get the voltage boost circuitry so that you can squeeze more out of the batteries on each charge. These parts cost <$2 and will do a much better job than something you whip up on your own at higher cost and trouble.

Still, I think you'll only get 2-3 nights out of a full charge unless you go to a larger battery pack (maybe 4 AAs in parallel?). Using a motion detector is a better suggestion.


Joined Sep 21, 2010
Hi Audioguru, I can asure you here in Austalia we have plenty of sunshine & these Leds will stay a light till morning when they switch off & the solar recharges the battery


Joined Apr 1, 2016
Is the DC-DC converter mentioned a Joule Thief? I don't see a coil. I would like to construct a circuit like this using a Joule Thief to use up old batteries my camera kicks out way too soon as weak. I can use the light for lots of uses, like a stink bug trap. Old batteries are usually not ni-cad, so solar charging is not necessary. I'm just wondering if a Joule Thief can come up with enough power to operate the daylight sensor circuit.