A disassembled Sharp GP2D15 sensor.

Special thanks to Jeff Paden for sharing this idea!

This note describes how to get shorter detection ranges with the Sharp GP2D15 sensor.  This sensor has a factory pre-set range of 24cm.  When an object is closer than 24cm, the digital output is high.  When an object is beyond 24cm, the digital output is low.  It is possible to set this detection range at some value between 10cm and 24cm by making a simple modification to the sensor package. 

The Sharp GP2D15 has a single screw on the back.  This screw holds the shell with the lenses and the circuit board together.  Adding a spacer between the circuit board and the shell moves the lenses a small distance away from the board.  This changes the optics slightly.  The result is a shorter detection range.  Getting longer detection ranges would require different lenses since the construction of the package prevents moving the shell closer to the board.  Along with its pre-set detection range, the Sharp GP2D15 sensor has a minimum range for getting correct readings.  If an object moves closer than 3 or 4 cm to the sensor, the output will go from high to low.  Moving the shell away from the circuit board will increase this minimum limit.  The new minimum limit may be as much as 5 or 6 cm.  A small change in the thickness of the spacer can make a significant change in performance.  Performance may also vary significantly from sensor to sensor. 

To perform the modification, remove the screw on the back of the unit.  Remove the shell.  Put the screw back in the circuit board.  Place a small spacer on the screw so that it will fit between the shell and the circuit board.  Carefully screw the shell back in place.  The shell should be parallel to the circuit board, not tilted or skewed in any direction.  Test the modified sensor to determine its new detection range and minimum limit.  Try different spacers to get a desired detection range. 

The screw is usually fastened very tightly in a new sensor.  It is easy to strip the top of the screw where it makes contact with the screwdriver.  If the screw is lost or damaged, it can be replaced with a standard 2mm x 5mm metric screw.  A tiny "1-72" washer makes a good spacer.  Several of these tiny washers can be stacked in the recess for the screw.  A hardware store with a large section for nuts and bolts will likely have tiny metric screws and washers. 

If "1-72" washers are unavailable, finding a spacer of the appropriate size may be difficult.  It may be necessary to make one from scratch.  One possibility is to make a spacer from perfboard.  A typical width for such a spacer is 2mm.  Cut a square of perfboard small enough so that it has only one hole.  Drill out the hole so that it will fit the screw.  Grip the perfboard firmly with a pair of pliers.  A tiny bit should protrude from the jaws of the pliers.  Carefully snip away the tiny bit of the perfboard with diagonal cutters.  Repeat this process until the spacer fits in the recess for the screw in the circuit board.  Another possibility is to use a small flat washer that may be larger than the recess for the screw.  It can lay over the recess on top of the circuit board cover.  Insert the screw through the board and washer and fasten the shell.  This will offset the shell by the thickness of the washer plus 2mm. 

Related Links:

Demystifying the Sharp IR Rangers

Sharp IR Range Finder Voltage-to-Range Conversion Article