Replace Photoresistor with Solar Cell

[galantida]

Hello All,

I am an electronics newbie with only a few projects under by belt. My current project it to create a target that when shot with a laser will fall over. Basically a solar cell which will trigger a transistor which will allow a 9 volt battery to power solenoid to knock the target over.

Right now I am trying to take simple night light circuit where a light comes on when its dark and replace the photo resistor with a solar cell. Since solar cells are a lot bigger target.

https://www.digikey.com/en/maker/blogs/2017/night-light-circuit-using-a-pnp-transistor

I want the light to go out when the solar cell is uncovered rather then when a photoresistor is uncovered. Every solar circuit I find on the internet wants to power the entire circuit with the solar cell or charge a battery with the solar cell. Neither of which I need for my project. I actually prefer having a regular old 9V battery in it.

I think its having a transistor connected to two different power sources that is throwing me. I have the Base of PNP hooked to the solar cell, the Emitter hooked to a 9 volt battery and the collector to the solenoid.

Any advice, or design direction I should explore.

 

[galantida]

Actually I just found this solar circuit which is very much like the night light one I am testing with. I just ditched the extra diode since I don't need the charging capabilities. Maybe the panel I am using is not putting out enough for the transistor I am using? I'll give another try tonight.
http://www.reuk.co.uk/wordpress/solar/use-solar-panel-as-darkness-detector/

 

[Hopup]

But why would you want to use solar cell instead? Might be easier with simple optics layer top of photo sensor.

 

[BobK]

If you solar cell puts out more than a half a volt, it is actually multiple cells in series. In this case, all of the cells must be activated ti get an output. In other words, illuminating a small part of the solar panel with a laser dot will not work.

Bob

 

[galantida]

Hopup, Concerning the optics layer. I was looking for something to scatter the light and couldn't figure out what to look for on Google. I know I have taken LEDs and hit them with some sand paper to scatter the light they put out and it worked well. Maybe I'll try a small piece of plexi glass buffed up on one side with sand paper and see if it glows enough to create a detectable resistance in the photo cell no matter where it is hit. If you know the name of some lens I could put on a photo resistor please share. In google "optics layer" just keeps returning results about fiber optic networking.

Bob, yea with a volt meter hooked up to the small solar cell I did get a tiny detectable bump when I hit it with the laser but depending on the ambient light this bump range might be hard for me to detect using simple electronics. I am a programmer by trade but I am trying not to introduce an Arduino to this project. You are probably right and this route is a dead end.

Thank you both for your replies, you gave me some stuff to think about. If you don't mind I'll do some more testing and share my results back here in this thread.

 

[Hopup]

Yes you wont probably find anything with that term, but you got what I meant some kind of mirror or lens to direct the light would be probably easy thing to do.

 

[(*steve*)]

One thing you might want to consider is modulating your laser. This will allow your receiving circuit to be much more sensitive as it will be able to distinguish the laser from other ambient sources.