Switch Swap: Photo Resistor

Thread Starter

StampedePete

Joined Aug 31, 2015
6
I'm working on a project roughly following a something in "Hacking Electronics" by Simon Monk but changing a number of variables. The basic idea is to create a light that uses a photo resistor to turn on or off automatically. Unlike the book's 1 LED I decided to get a small 23 LED push light. It takes 3 AAA batteries for a total of 4.5v.

The original project calls for a 2n3904, a photoresistor and a few resistors. I tried a number of resistor values but at best with an extremely low Resistor Value and with the photo resistor removed, I got an extremely dim output from the LEDs.

Any advice to steer me in the right direction?
 

AnalogKid

Joined Aug 1, 2013
10,987
Stop and think for a minute. Do you really expect a critique of a circuit you won't share, that has modifications you won't describe, with no component values, connections, etc. Really?

"What's his plan? ... Russians don't take a dump, son, without a plan."
- Rear Admiral Joshua Painter to Jack Ryan, "The Hunt For Red October", (1990)

An engineer don't take a dump, son, without a schematic.

ak
 

ian field

Joined Oct 27, 2012
6,536
I'm working on a project roughly following a something in "Hacking Electronics" by Simon Monk but changing a number of variables. The basic idea is to create a light that uses a photo resistor to turn on or off automatically. Unlike the book's 1 LED I decided to get a small 23 LED push light. It takes 3 AAA batteries for a total of 4.5v.

The original project calls for a 2n3904, a photoresistor and a few resistors. I tried a number of resistor values but at best with an extremely low Resistor Value and with the photo resistor removed, I got an extremely dim output from the LEDs.

Any advice to steer me in the right direction?
Its getting harder to obtain CdS photo resistors because the cadmium is very toxic.

When the security lights were upgraded at the flats, they ripped out some outdoor luminaires that had daylight shut off. A couple of them had mains rated CdS cells in series with the element on a bi metal strip thermal relay. A couple used a IR photo diode very similar to the ones in less recent CTVs for the remote control. Despite being IR photo diodes - they seemed to work well enough sensing daylight.

The electronic version used a LM358 dual op-amp. The first amp as a voltage follower to respond to the low leakage current in the illuminated PD, The second stage was a Schmitt trigger - that was directly driving the gate of a triac.

When I first posted the schematic; it was removed because its a transformerless mains circuit - I blocked out the naughty bit and posted it again - so it should be floating about somewhere.
 

GopherT

Joined Nov 23, 2012
8,009
Still plenty for sale though. Digikey, for example, lists 49 CdS photocells.
They are just teasing you. Those are for big kids who are allowed to play with such things - that is, those of us outside the EU's REACH & RoHS programs. In 10 or 20 years the UK might figure out how to Brexit and you can, again, have night lights.
 
Top