I'm trying to make a battery-operated, microcontroller-controlled, short-range, laser range-finder. It needs to be very light (weight-wise).
Does anyone know of a reliable method of detecting reflected green laser light from about 50 feet from a grassy surface in an outdoor environment? The grass seems to reflect a sizeable amount of light back to the source (at least by eyballing it). It seems a detector should be able to differentiate the presence or absence of the laser light. The green laser light seems to reflect better than red on a grassy field. I have a very small, light-weight green laser module which is suitable to my application but now I need to develop a reflected light detection system.
I have tried a phototransistor (Panasonic PNZ121S0R) but it didn't seem to pick up any changes at about 10 feet onto a fairly glossy hardwood surface (wood panelling). When I try the laser directly into the phototransistor over about 10 feet distance, it worked very well, though. I had the collector pulled up to 4.5VDC (3 AA cells) and the emitter grounded. The collector showed about 4.5VDC with no laser light and about 0.15VDC with direct laser light. With the reflection, though, there was no change at the collector from the 4.5VDC. I verified the detector was aligned with the reflected light. I even tried a small straw as an ambient light reducer but no change.
I then tried a photoresistor. It seems to be a little more responsive. With just an ohmmeter across the leads, it showed a quiescent resistance of about 100K and when it sees the reflected light, it drops to about 85K or
90K. This was inside in a flourescent light environment, though. I did use a guide tube (straw) with the photoresistor and it helped significantly in reducing the ambient light. I thought I could use the photoresistor in a comparator circuit to set a range of operation.Any thoughts or experience would be appreciated.
Thanks.
Dave