photosensor value question

You could use resistors or a 5 M pot to figure out the settings needed.

But is it worth it? These things are about $10 right?

Thanks for the idea - unfortunately I can't buy a sensor module by itself, it's a fairly complex circuit. The lamp uses a photosensor to turn the light itself on and off and has a second stage that uses an ultrasonic sensor to detect motion. The lamp is off during the day and either on at night at half power or on full brightness when it detects motion. Plus, there are switches to set the intervals for how long it is on full bright after detecting motion and how long the lamp stays on after sunset.

I've found an identical replacement lamp on Ebay for about $50 plus shipping and I'd rather not need to spend in the area of $65 with shipping to replace the whole thing.

Also, >

Is the one that doesn't work stuck in the on or off position? Also, is there an adjustment for the on/off threshhold somewhere on your device? What happens when you adjust it from min to max and back again?

It's possible to measure resistances outside your ohmmeter's range. Get a 1 Mohm resistor, measure it's resistance. Put your photsensor in parallel with the 1 Mohm, and measure the resistance again. Use a little algebra to solve for the unknown resistance:

where Runk is the unkonwn resistor Rpar is the measurement of the parallel combination. Rref is the measurement of the 1 Mohm (or the highest, measureable resistor that you have lying around)

This would have reasonable accuracy for 20 Mohm resistors, but probably is rather innaccurate for 500 Mohms, though you'd still have a ballpark value.

Mark

It's stuck on. The only adjustment that I can see is for setting the motion sensing range and not the day/night trigger which turns the light on after the photosensor sees that it is dark already.

I'm going to give that a shot as well. I came across a meter here that has a 4m ohm range and I'm ordering a new (better) meter along with the photocells since I need a better one anyhow.

It would be good to make sure the photosensor is really the cause of the problem. You could replace it with a small resistor, say 100 ohms, and see if that shuts off the light. If not, then the problem is somewhere else in the circuit.

Mark