Let's Make Robots!

Sharp IR distance sensor improvement

Improves the obstacle recognation of Sharp IR distance sensors

Sharp IR distance sensors are very often used in robotics. But I always found it annoying, that they do not recognize very small objects, chair legs or even walls if the Sharp IR is set to an unfavorable angle to the wall. Here is the idea I came up:

 

The internal IR LED is disconnected from the Sharp IR distance sensor LED driver:

The LED driver triggers now a PNP transistor and this transistor triggers again a couple of IR LEDs which are placed around the Sharp sensor as close as possible to the original LED, because the CCD seems to be anisotropic. Reflection from the oposite direction of the original LED are ignored:

What it actually does is that:

 

On my prototype are four 3mm IR LEDs placed around the Sharp (the 2 LEDs on the left do not have any influence on the measuring, which I found out later). The sensor is now able to detect a 3mm diameter steel rod at 25 cm distance.

Further developements could include:

  • LADAR (using an IR Laser instead of the IR LEDs)
  • Object tracker (switching LEDs on/off before measurement)
  • Increasing/decreasing max. distance reading by controlling the driver transistor

*** Update 2011.6.19 ***

Just a small rendering how a costum PCB for the Sharp could look like. The IR laser diode sitting on the place of the original IR LED. A driver for the IR laser diode is then necessary:

 

*** Update 2011.6.25 ***

Sharp Ladar prototype finished. The IR Laser has 30mW. The laser has three wires, red, black, and yellow. By setting the yellow wire high or low you can enable/disable the laser. This is a great feature for control. The laser has an adjustable focus as well.

LADAR mounted on RoverX:

Original voltage/distance graph vs voltage/distance graph with laser instead of built in IR LED (new graph not scaled):

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

With a laser do you risk the beam being so narrow that you miss an object that a wider beamwidth LED would catch?

I wonder if you could do a mix of 2 LEDs and an IR laser? Then you'd get the best of both worlds.

Most laser assemblies have an adjustable focus. By taking it slightly out of focus you get a large red spot. This can help prevent you from missing anything.

Because the laser light is now shining over a larger area you do loose some intensity but considering Markus is using a 50mW laser and has a new born baby in the house I think this might be a good idea.

Definetely I will not use a 50mW laser in the same room where my baby is.

The laser I have ordered has an adjustable focus, btw.

Yes, I thougt about this. You could do hybrid, first switch on the LED's for closer object detection, then the Laser for objects at greater distance. The laser should be place above the original IR LED.

Hi OB,

The readings are different. First of all you don't have a "zero" reading anymore if the object is very close (5mm). Then I found out the LEDs should be placed as close as possible to the original LED. LEDs placed a few centimeter away, do not affect the measurement, at least not my small 3mm LEDs. The CCD array seems to be anisotropic. Reflection from the oposite direction of the original LED are ignored:

 

Very nice. Considering the sensor works on triangulation of a single reflection I wonder how it's accuracy will be affected by multiple reflections from multiple sources?

I do not know what LEDs you are using but I have found (according to the datasheets) that the 5mm LEDs always have a better light output for the same amount of power used.

I have always wanted to do someting similar but using a laser in place of the IR LED to increase range while improving accuracy when doing a sweep.

Yeah, have already made the schmeatic for this and ordered an IR laser at taobao (50 mW).