Designing A
Low Cost Laser
— Part 2
Last time, I introduced the Laser
Range Finder (LRF) project and
discussed my initial work in designing
a low cost module that can detect the
distance to a target object using a
laser and camera. I had proved the
concept of using optical triangulation
and was successful in obtaining an
image with my prototype circuitry. The
article continues here with a look into
the final hardware design and
functionality of the device.
LRF Hardware
Confident that the camera interface was functioning
properly, it was time to finalize the design and move away
from my Propeller proto board-based development platform
onto a custom PCB containing only the electronics required
for the LRF (see Figures 1A and 1B).
The PCB for the LRF module is four layers and measures
3.95” x 1.55” (~100 mm x 39 mm). All components are
by Joe Grand
www.servomagazine.com/index.php?/magazine/
article/november2011_Grand
mounted on the back side of the board with the exception
of the camera module (which is so tiny it can barely be
seen on the left side of the PCB) and the laser diode. The
Propeller, its supporting electronics, and the camera
interface circuitry can be seen on the right of the back side
image; the laser diode control circuitry is on the left. A Prop
Clip/Plug four-pin interface (used for Propeller
programming) is at the top of the board as surface-mount
pads. Below it is a bi-color (red/green) LED for indication of
system status. At the bottom is a single row, four-pin
header (serial IN, serial OUT, VCC, GND) for the primary
user interface (sending commands and receiving data).
The center points of the camera and laser diode are
spaced at exactly 78 mm which closely matches the spacing
of my proof-of-concept (and the original project on which
my project is based), and keeps the module to a reasonable
size. The spacing of the camera and diode ultimately
determines the effective range (minimum and maximum
detectable distance).
The major hardware components include the Propeller,
serial EEPROM for Propeller firmware and unit configuration
data, OVM7690 camera, PCA9306 level translator, laser
A
FIGURE 1 A and B.
B
40 SERVO 11.2011
