Product: Sharp GP2Y0D810Z0F Digital Distance Sensor 10cm
I ordered a group of these sensors and some (not all) of them seem to have a dead spot in the center of their detection range (that range being about 2cm-10cm). An object placed in front of the sensor near the ends (2 or 10 cm) provides a strong clear signal. Towards the middle you can see the on-board LED flashing, and at a certain spot in the center some lose detection entirely.
As I said, not all of the sensors are doing this, which I find strange. Initially I thought it might have something to do with my circuit or I damaged them somehow when soldering, but I started testing them straight out of the package (hooked directly to a power supply set to 5V) and saw the same effect.
From searching it seems the “go-to” fix for these sensors is to add a capacitor (10uF or more!) between power and ground, but I’ve only seen that suggested for different issues. Couldn’t find anyone mentioning the same problem I’m seeing on this forum. Would the cap help in this case? The sensor clearly CAN provide a constant proper signal (at the right range).
Thanks for any help!
Update: This problem is related to the material reflecting, even a “bad” sensor seems to work 100%, or nearly, with the right material. Maybe if you get the combination of a “weaker” sensor, a material that is less easily measured, and the middle distance which is the “worst” spot to measure, you get this phenomenon?
Hello.
The performance of the Sharp GP2Y0D810Z0F digital distance sensors will rely heavily on the material you use. I have not heard of them having this kind of dead spot you are describing, but it could have a lot to do with your setup.
Could you post some more details about your test setup? Pictures of how everything is positioned might be helpful. What kind of material are you trying to detect? Keep in mind that the angle of the surface can also be a factor since the IR light reflected needs to make it back to the sensor.
By the way, the capacitor is recommended because these sensors tend to draw spikes of current in quick bursts, which can be a problem depending on your power supply. I would recommend adding the capacitors even if you think your power supply can handle the spikes, especially if you are seeing some inconsistent behavior without them.
Brandon
To add a few more details, I’m wiring these up to the power/ground node of a small circuit board, with the signal wire going to the gate of a PNP mosfet. I don’t think that matters too much, because as I’ve said I hooked one up directly to the Tektronix DC power supply I’ve been testing with (without nothing on the output signal pin) and still got the same behavior.
I’m going to be detecting a robot which I already discovered has plastic that absorbs the IR, but paper taped to it fixed that problem. I was just testing the sensor with materials around however. PVC is apparently very reflective and fixes the issue. My hand, the table, and cardboard are not.
I figured it wasn’t bad enough to interfere with my purpose, but for one particularly bad sensor I tried adding a 33uF cap and sure enough that fixed it. So some combination of less-than-ideal sensing situation (worse materials or angled off) plus power issues without the capacitor leads to the dead spot in the middle only. Still would clear signal at the ends of the range.
Seems strange, but I know how to fix it for any sensors that are an issue. I’d recommend adding the cap to the Pololu board itself perhaps.
Thanks for the additional details about your setup. I am glad you are able to get it working better with the added capacitor. Our carrier board does add enough capacitance for typical applications. There are a variety of reasons for not including more on the board itself, including keeping the board as compact as possible and reducing the potential for damaging LC voltage spikes, and it’s usually easy to put some additional capacitors across power and ground in the final application if required.
Brandon
