damage

should

someone

lo

ok

in

to

the

laser

at

v

ery

close

range 

The

p

erformance

of

the

laser

driv

e

circuitry

allo

ws

the

laser

to

b

e

mo

dulated

w

ell

ab

o

v

e

the

required

  MHz 

Optical

Assem

blies

The

optical

system Fig 

had

to

b

e

as

simple

as

p

ossible 

y

et

allo

w

for

alignmen

t

adjustmen

ts

in

all

axes 

This

w

as

accomplished

b

y

sho

oting

the

laser

at

a

righ

t

angle

to

the

lens

tub

e

of

the

camera 

A

mirror

w

as

p

ositioned

under

the

lens

tub

e

to

re ect

the

laser

along

the

cen

tral

axis

of

the

scanner 

The

mirror

can

b

e

angled

up

and

do

wn

as

w

ell

as

left

and

righ

t 

Although

the

laser

is

v

ertically

displaced

from

the

camera s

view 

the

mirror

is

adjusted

suc

h

that

the

laser

fo

cuses

at

in nit

y

on

to

the

cen

ter

of

the

photo

dio

de 

This

geometry

enables

ob

jects

to

b

e

detected

when

they

are

displaced

at

least

from

the

mirror 

A

photo

of

the

actual

re ned

scanning

assem

bly

app

ears

in

Fig 

One

migh

t

think

that

the

b

est

solution

w

ould

b

e

to

use

a

b

eam

splitter 

but

the

loss

of

optical

p

o

w

er

on

the

receiv

e

end 

together

with

some

di cult

y

in

remo

ving

residual

re ection 

w

ould

not

b

e

acceptable

in

this

design 

An

option

for

future

designs see

Fig 

could

emplo

y

the

tric

k

of

drilling

a

small

hole

in

a

mirror 

angled

at

degrees

in

fron

t

of

the

lens 

The

laser

could

then

b

e

shot

through

the

hole 

As

the

lens

is

m

uc

h

bigger

than

the

hole 

the

lost

area

of

the

hole

giv

es

insigni can

t

loss

in

the

amoun

t

of

laser

ligh

t

arriving

at

the

receiv

er 

This

con guration

w

ould

require

the

least

adjustmen

t

of

all 

as

the

laser

and

camera

views

w

ould

b

e

colinear 

The

lens

and

the

scanning

mirror

are

aligned

to

scan

through

appro

ximately

degrees 

The

scanning

mirror

is

a

surplus

stepp

er

motor

 tted

with

a

mac

hined

sided

mirror

moun

t 

Eac

h

facet

is

wide

b

y

high 

This

allo

ws

the

lens

to

collect

a

reasonable

amoun

t

of

ligh

t

across

the

scan 

Tw

o

phototransistors

are

moun

ted

on

eac

h

end

of

the

scanning

range

 lab

eled

stop

and

start

in

Figs 

and

The

collectors

of

the

transistors

are

pulled

up

to

v

olts

with

a

resistor

in

parallel

with

a

 ltering

capacitor 

The

collector

signals

are

conditioned

b

y

a

bu er 

The

pullups

and

the

bu ers

are

lo

cated

on

the

demo

dulator

b

oard 

This

generates

a

clean